Engine Controls Self-Diagnostics - 3.1l Engine Buick Century VI

INTRODUCTION

To properly diagnose and repair this vehicle, follow DIAGNOSTIC STARTING POINT - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. If no Diagnostic Trouble Codes (DTC) are present and a no-start condition exists, proceed to NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no DTCs are present and a driveability condition exists, proceed to TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

ON-BOARD DIAGNOSTICS

The Powertrain Control Module (PCM) constantly looks at the information from various sensors and other inputs and controls systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the Malfunction Indicator Light (MIL). When the PCM detects a malfunction, the PCM stores a Diagnostic Trouble Code (DTC). The problem area is identified by the particular DTC that is set. The PCM supplies a buffered voltage to various sensors and switches. The input and output devices in the PCM include analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that complete a ground or voltage circuit when turned on. Most PCM controlled components are operated via output drivers. The PCM monitors these driver circuits for proper operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is detected.

PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will store a DTC and, if DTC is emissions related, the MIL is illuminated. The following are some of the functions that the PCM controls

1. The engine fueling.
2. The Ignition Control Module (ICM).
3. The Knock Sensor (KS) system.
4. The Evaporative Emissions (EVAP) system.
5. The Secondary Air Injection (AIR) system (if equipped).
6. The Exhaust Gas Recirculation (EGR) system.
7. The automatic transmission functions.
8. The generator.
9. The A/C clutch control.
10. The cooling fan control.

There are 2 paths for accessing on-board diagnostics. It is necessary to access information through both paths, as each path presents some different information.

1. Generic OBD-II - This provides all generic codes and some OEM codes, serial data PIDs required for generic OBD-II and some OEM PIDs, monitor status, pending codes and freeze frame.
2. OEM - All DTCs, all PIDs, failure records, enhanced scan tool information and all other OEM scanner functions.

Code Types

There are 3 types of DTC categories

1. Type "A" - Emissions related. PCM illuminates the MIL when the diagnostic runs and fails.
2. Type "B" - Emissions related. PCM illuminates MIL on the second consecutive ignition cycle that the diagnostic runs and fails.
3. Type "C" - Non-emissions related. PCM stores the DTC information into memory when the diagnostic runs and fails. The MIL will not illuminate. The Driver Information Center (DIC), if equipped, may display a message.

DTC Status

When the scan tool displays a DTC, the status of the DTC is also displayed. The following DTC statuses are indicated only when they apply to the DTC that is set.

Freeze Frame/Failure Records

PCM stores one freeze frame record for the first failed test that sets a DTC and illuminates MIL. Freeze frame will not be overwritten unless a misfire or fuel trim DTC is set. Failure records are stored when any DTC is set. Some PCMs can store up to 5 failure records. Failure records will be stored for all types of codes, whether or not MIL is illuminated.

Typical data includes

1. Air/fuel ratio.
2. Air flow rate.
3. Fuel trim.
4. Engine speed.
5. Engine load.
6. Engine coolant temperature.
7. Vehicle speed.
8. Throttle position angle.
9. Manifold absolute pressure.
10. Injector base pulse width.
11. Loop status.

Monitors

1. Comprehensive Component Monitor - Monitors PCM systems for opens, shorts grounds and out-of-range sensors. Also monitors rationality of sensors. Rationality is whether the sensor value is consistent with the operating conditions of the other sensors.
2. Misfire Monitor - Monitors engine misfire using crankshaft sensor to determine location and severity of misfire. A catalyst damaging misfire will flash the MIL, and a non-catalyst damaging misfire is a normal type "B" code.
3. Fuel Trim Monitor - Monitors short and long term fuel trim for being at maximum lean or rich limit.
4. Oxygen Sensor Monitor - Monitors all oxygen sensors for maximum voltage level, minimum voltage level and lean rich/rich lean switching rate.
5. Oxygen Sensor Heater Monitor - Monitors oxygen sensor heater by watching sensor's time-to-activity after a cold start.
6. Catalyst Monitor - Monitors catalyst efficiency by comparing activity rate of pre-catalyst oxygen sensor and post-catalyst oxygen sensor.
7. EVAP Monitor - Monitors EVAP system for large leaks, small leaks and purge flow.

DIAGNOSTIC STARTING POINT - ENGINE CONTROLS

Begin the system diagnosis with Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS . The Diagnostic System Check - Engine Controls will provide the following information

1. The identification of control modules which command the system.
2. The ability of control modules to communicate through serial data circuit.
3. The identification of any stored Diagnostic Trouble Codes (DTCs) and the codes' statuses.

The use of the Diagnostic System Check - Engine Controls will identify the correct procedure for diagnosing the system and where the procedure is located.

RETRIEVING DIAGNOSTIC TROUBLE CODES

DTCs are retrieved using a Tech 2(R) scan tool or other OBD-II compatible scan tool connected to OBD-II 16-pin Data Link Connector (DLC). See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS . DLC is located below left side of dash.

CLEARING DIAGNOSTIC TROUBLE CODES

There are 3 methods to clear DTCs.

Scan Tool

Scan tool is preferable way to clear DTC information. Freeze frame and failure record data will also be cleared. PCM adaptive learning and system monitors will only be cleared for those system which had a stored DTC. A current DTC Last Test Failed clears when the diagnostic runs and passes.

Disconnect Battery

Note. On many OBD-II systems, PCM will retain memory for an extended period of time with battery disconnected. Memory may be retained for several days.

Disconnecting PCM power or battery ground will clear all PCM memory including DTCs, freeze frame, failure records, adaptive learning and system monitors.

Warm-Up Cycles

The PCM uses warm-up cycles to run some diagnostics and to clear any Diagnostic Trouble Codes (DTCs). A warm-up cycle occurs when the engine coolant temperature increases 72°F (22°C) from the start-up temperature. The engine coolant must also achieve a minimum temperature of 160°F (71°C). The PCM counts the number of warm-up cycles in order to clear the Malfunction Indicator Light (MIL). The PCM will clear the DTCs when 40 consecutive warm-up cycles occur without a malfunction.

Description

The Diagnostic System Check - Engine Controls is an organized approach to identifying a condition created by a malfunction in the engine control system. The Diagnostic System Check must be the starting point for any driveability concern. The Diagnostic System Check directs the service technician to the next logical step to diagnose the concern. Understanding and correctly using the diagnostic table reduces diagnostic time and prevents the replacement of good parts.

Test Description

The numbers below refer to the step numbers on the diagnostic test procedure.

1. 2 - Lack of communication may be a result of a partial or a total malfunction of the class 2 serial data circuit. The specified procedure determines the particular condition.
2. 5 - This step stores the PCM DTC information into the scan tool's memory. After you complete the diagnostic procedure, review the captured information to catch the next DTC if the PCM stores multiple DTCs. Review the Freeze Frame/Failure Records data. Use this information to determine how frequently and how recently the DTC set. This information may help diagnose an intermittent condition. Information about the operating conditions at the time that the DTC set may also help diagnose an intermittent condition. Capturing the stored information saves the data that the PCM loses during the following conditions: When a diagnostic procedure instructs you to clear DTCs. When a diagnostic procedure instructs you to disconnect the PCM harness connectors. When a diagnostic procedure instructs you to replace PCM.
3. 6 - The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests.
4. 8 - If there are other modules with DTCs set, refer to the DTC list. The DTC list directs you to the appropriate diagnostic procedure. If the PCM stores multiple powertrain DTCs, diagnose the DTCs in the following order: Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic table directs you otherwise. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.
5. 10 - This step is for areas that have inspection and maintenance testing procedures for emissions testing. Use this step if the testing facility found one or more I/M system statuses that did not set.

Diagnostic Procedure

Note. DO NOT perform this test if no driveability condition exists. Search for applicable bulletins before proceeding with this test. DO NOT turn OFF ignition when performing this diagnostic test procedure. DO NOT clear the DTCs unless the diagnostic instructs you to do so. If there is a condition with the starter system, diagnose starter system. See appropriate STARTERS article in STARTING & CHARGING SYSTEMS. Ensure battery is fully charged and cables are clean and tight. Ensure PCM grounds are clean, tight, and in proper location.

1. Connect scan tool. Does scan tool power up? If yes, go to next step. If no, perform SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
2. Turn ignition switch to RUN position, engine off. Using scan tool, attempt to establish communication with the Instrument Panel Cluster (IPC), Powertrain Control Module (PCM) and Vehicle Theft Deterrent (VTD). Does scan tool communicate with all the control modules? If yes, go to next step. If no, perform SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
3. Attempt to start engine. Does engine start and idle? If yes, go to next step. If no, go to «NO-START DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__no-start-diagnosis) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Using scan tool, select the DTC display function for the Powertrain Control Module (PCM), Vehicle Theft Deterrent (VTD) and Instrument Panel (I/P) Cluster. Does scan tool display any DTCs? If yes, go to next step. If no, go to step 9 .
5. Using scan tool, select CAPTURED INFO to store the powertrain DTC information. When complete, go to next step.
6. Does scan tool display DTCs which begin with a "U"? If yes, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If no, go to next step.
7. Were any of PCM DTCs P0601 or P0602 set? If yes, go to «DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683 OR P2610: ECU MALFUNCTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0601-p0607-p1600-p1621-p1627-p1680) under DIAGNOSTIC TESTS. If no, go to next step.
8. Does scan tool display DTC P0562, P0563, P0621 or P0622? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
9. Is customer's concern with the automatic transmission? If yes, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If no, go to next step.
10. Is customer's concern with the Inspection/Maintenance (I/M) testing? If yes, go to «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under INSPECTION/MAINTENANCE PROCEDURES. If no, go to next step.
11. Check for the following symptoms. For diagnosis, go to «TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l) article: Hard start. Surges/chuggles. Lack of power, sluggishness, or sponginess. Detonation/spark knock. Hesitation, sag, stumble. Cuts out/misses. Poor fuel economy. Rough, unstable, or incorrect idle and stalling. Dieseling/run-on. Backfire. MIL inoperative. For repair, see «MIL INOPERATIVE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__mil-inoperative) under SYSTEM TESTS. MIL always on. For repair, see «MIL ALWAYS ON»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__mil-always-on) under SYSTEM TESTS. Repair as necessary. If no problem is found, problem is intermittent. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

SCAN TOOL USAGE

Scan tool is a specialized tester which, when connected to DLC, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.

Scan tool reduces diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by PCM; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light.

A problem may exist even if DTCs are not present. Many driveability problems occur without setting DTCs.

Using a scan tool is the easiest method of checking sensor specifications and other data parameters. Scan tool is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters.

Note. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, DO NOT use scan tool for diagnosis. Contact tester manufacturer for additional information.

Scan Tool Display

Note. OBD-II vehicles have options available in the scan tool DTC mode to display enhanced information available. However, to fully utilize information and procedures requires the use of a Tech 2(R) scan tool. See scan tool operator's manual for additional information.

The following DTC statuses are indicated only when they apply to the DTC set

1. Fail This Ign. (Fail This Ignition) - Indicates that this DTC failed during the present ignition cycle.
2. Last Test Fail - Indicates that this DTC failed the last time the test ran. The last test may have run during a previous ignition cycle if an "A" or "B" type DTC is displayed. For type "C" DTCs, the last failure must have occurred during the current ignition cycle to appear as last test fail.
3. MIL Request - Indicates that this DTC is currently requesting the MIL. This selection will report type "B" DTCs only when they have requested the MIL (failed twice).
4. Test Fail SCC (Test Failed Since Code Clear) - Indicates that this DTC that has reported a failure since the last time DTCs were cleared.
5. History - Indicates that the DTC is stored in the PCM History memory. Type "B" DTCs will not appear in History until they have requested the MIL (failed twice). History will be displayed for all type "A" DTCs and type "B" DTCs (which have requested the MIL) that have failed within the last 40 warm-up cycles. Type "C" DTCs that have failed within the last 40 warm-up cycles will also appear in History.
6. Not Run SCC (Not Run Since Code Clear) - DTCs will be listed in this category if the diagnostic has not run since DTCs were last cleared. This status is not included with the DTC display since the DTC can not be set if the diagnostic has not run. This information is displayed when DTC Info is requested using the scan tool.

POWERTRAIN CONTROL MODULE LOCATION

On Century and Grand Prix, PCM is located left side of engine compartment, inside air cleaner assembly. (Scheme 19) On Malibu, PCM is located under Instrument Panel (I/P), next to Data Link Connector (DLC). (Scheme 20)

PROGRAMMING

Note. DO NOT program an existing PCM with the identical software/calibration package. This procedure is not a short cut to correct a driveability condition. This is an ineffective repair. A PCM should only be programmed when a service procedure instructs you to replace the PCM. The service part PCM does not contain operating software or calibrations or General Motors Corporation releases an updated software/calibration package.

After replacing Powertrain Control Module (PCM) or if program needs to be updated, refer to latest Techline(R) information on PCM reprogramming. PCM can only be programmed using Tech 2(R) and Techline(R) terminal, or by using a personal computer equipped with the current service programming system software installed.

Ensure that the following conditions are met before programming a control module

Service Programming System

The Service Programming System (SPS) allows a technician to program a control module through the Data Link Connector (DLC). The information transfer circuit that is used at the DLC is the same serial data circuit used by the scan tool for retrieving Diagnostic Trouble Codes (DTCs), displaying data, clearing DTCs, etc. This procedure offers the ability to install software/calibrations matched to a particular vehicle. Most control modules have 2 types of memory. The software/calibrations reside in the flash memory. The 2 types of memory are listed below

1. Electrically Erasable Programmable Read Only Memory (EEPROM) - This type of memory allows selected portions of memory to be programmed while other portions remain unchanged. Certain learned values reside in the EEPROM, such as; Vehicle Identification Number (VIN), crankshaft variation learned position, software/calibrations identification numbers and control module security information.
2. Flash Read Only Memory - Flash Memory Flash memory has increased memory storage capacity. During programming, all information within this type of memory is erased, and then replaced with entirely new information.

Service Programming Methods

The 4 methods of programming a PCM and the proper tools for each method are as follows

1. Remote Programming - The Tech 2(R) or other scan tool, Techline Terminal or a personal computer equipped with General Motors Corporation authorized programming software. The Tech 2(R) or other scan tool is used as an interface between the vehicle and the Techline Terminal or a personal computer. See «SERVICE PROGRAMMING SYSTEM REMOTE PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__service-programming-system-remote-procedure) .
2. Pass Thru Programming - The Tech 2(R) or other scan tool, Techline Terminal or a personal computer equipped with General Motors Corporation authorized programming software. The Tech 2(R) or other scan tool is used as an interface between the vehicle and the Techline Terminal or a personal computer. See «SERVICE PROGRAMMING SYSTEM PASS-THRU PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__service-programming-system-pass-thru-procedure) .
3. Off-Board Remote Programming, vehicle NOT available - The Tech 2(R) or other scan tool, Off-Board Programming Adapter (OBPA), Techline Terminal or a personal computer equipped with General Motors Corporation authorized programming software. The Tech 2(R) or other scan tool is used as an interface between the vehicle and the Techline Terminal or a personal computer. See «SERVICE PROGRAMMING SYSTEM OFF BOARD REMOTE PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__service-programming-system-off-board-remote) .
4. Off-Board Pass Thru Programming - The Tech 2(R) or other scan tool, Off-Board Programming Adapter (OBPA), Techline Terminal or a personal computer equipped with General Motors Corporation authorized programming software. The Tech 2(R) or other scan tool is used as an interface between the vehicle and the Techline terminal or a personal computer. The control module is NOT installed in a vehicle. See «SERVICE PROGRAMMING SYSTEM OFF BOARD PASS-THRU PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__service-programming-system-off-board-pass-thru) .

All 4 methods may not be available for every vehicle.

Before Programming A Control Module

1. Vehicle system voltage: There are no charging system concerns. All charging system concerns must be repaired before programming a control module. The battery voltage is greater than 12 volts but less than 16 volts. The battery must be fully charged before programming the control module. A battery charger is NOT connected to the vehicles battery. Incorrect system voltage or voltage fluctuations from a battery charger may cause programming failure or control module damage. Turn OFF or disable any system that may put a load on the vehicles battery. Turn OFF or disable Daytime Running Lights (DRL), applying the parking brake, on most vehicles, disables the DRL system. Heating, Ventilation, and Air Conditioning (HVAC) systems, engine cooling fans, etc.
2. The ignition switch is in the proper position. The scan tool prompts you to turn the ignition switch to RUN position, with the engine OFF. DO NOT change the position of the ignition switch during the programming procedure unless instructed to do so.
3. All tool connections are secure: The RS-232 cable. The connection at the DLC. The voltage supply circuits. The OBPA.
4. DO NOT disturb the tool harnesses while programming. If an interruption occurs during the programming procedure, programming failure or control module damage may occur.
5. If you are performing the pass-through programming procedure using a notebook computer without the power cord, ensure that the internal battery is fully charged.

After Programming A Control Module

The powertrain may operate slightly different after a control module software/calibration update. Operating the powertrain through various driving conditions allows the control module to re-learn certain values. The control module must re-learn the following after a software/calibration update

1. Fuel trim correction.
2. Idle Air Control (IAC) learned position.
3. Automatic transmission shift adapts.

If a control module is replaced the following service procedures may need to be performed

1. The crankshaft variation learn procedure.
2. The engine oil life reset procedure.
3. The idle learn procedure.
4. The inspection/maintenance complete system set procedure.
5. The Vehicle Theft Deterrent (VTD) password learn procedure.
6. The Throttle Position (TP) sensor learn procedure.

SERVICE PROGRAMMING SYSTEM REMOTE PROCEDURE

The Remote Service Programming System (SPS) method is a three-step process that involves the following procedures

1. Connecting the Tech 2(R) to the vehicle and obtaining the information from the module.
2. Connecting the Tech 2(R) to the terminal and downloading a new calibration file from the terminal into the Tech 2(R) memory.
3. Reconnecting the Tech 2(R) to the vehicle and uploading the new calibration file into the module.

Remote Procedure

Note. Ensure the PCM is installed in the vehicle and the battery is fully charged before programming.

1. Connect the Tech 2(R) to the vehicle and obtain the module information using the following procedure: Connect the Tech 2(R) to the vehicle Data Link Connector (DLC), with the engine and the Tech 2(R) OFF. (Scheme 1) Turn ON the Tech 2(R). Press ENTER at the title screen. Turn ignition switch to RUN position, engine OFF. Select SERVICE PROGRAMMING SYSTEM at the Main Menu. NOTE: Select REQUEST INFO AGAIN if a vehicle identification number (VIN) was previously stored in the Tech 2(R). Select REQUEST INFO. Enter the vehicle description by following the on-screen instructions. Turn all accessories OFF and select CONTINUE. Select NO and write down the VIN if the VIN is incorrect. Verify that the correct VIN is entered on the Tech 2(R) and select YES.
2. Turn OFF the Tech 2(R).
3. Disconnect the Tech 2(R) from the vehicle.
4. Turn ignition switch to OFF position.
5. Transfer the data from the terminal to the Tech 2(R) using the following procedure: Connect the Tech 2(R) to the terminal. (Scheme 2) NOTE: The TIS supports service programming with the Tech 2(R) scan tool only. Launch the TIS application at the terminal. Select the SERVICE PROGRAMMING SYSTEM at the main screen. Highlight the following information on the SELECT DIAGNOSTIC TOOL and PROGRAMMING PROCESS SCREEN: Select Diagnostic Tool - Select TECH 2(R). Select Programming Process - Identify whether an existing module is being reprogrammed or a module is being replaced with a new one. Select ECU Location - Select vehicle. Select NEXT. Verify the connections and select NEXT. NOTE: You may receive a message stating that the PCM could be a service PCM if you selected NO to the VIN being correct. Click OK. Verify the VIN and select Next. Select the appropriate controller for the vehicle being serviced. NOTE: When selecting the Vehicle Configuration Index (VCI) programming type, a valid VCI number for the vehicle must be entered. This number may be obtained from the Techline Customer Support. Select the type of programming to be performed from the following categories: Normal - Used for updating an existing calibration or programming a new controller. Vehicle Configuration Index (VCI) - Used for updating an existing controller or programming a new controller for newer vehicles whose VINs are not yet in the database. Reconfigure - Used to reconfigure a vehicle for changes in tire size and axle ratios. Select NEXT. NOTE: Refer to Service bulletins before service programming is performed if the bulletins are listed along with the calibration files. Select the appropriate calibration file for the vehicle being serviced. Select NEXT. NOTE: Select CANCEL if you receive a message stating that the calibration selected is already the current calibration in the PCM and reprogramming with the same download is not allowed. Verify your selection on the Summary screen. Select NEXT.
6. Perform the CRANKSHAFT POSITION VARIATION RELEARN PROCEDURE using the SPECIAL FUNCTIONS feature, if applicable. See «CKP SYSTEM VARIATION LEARN PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__ckp-system-variation-learn-procedure).
7. Close the application and return to the TIS application Selection screen after the download is complete.
8. Turn OFF the Tech 2(R).
9. Disconnect the Tech 2(R) from the terminal.
10. Transfer the data from the Tech 2(R) to the PCM using the following procedure: Connect the Tech 2(R) to the vehicle DLC, with the engine and the Tech 2 OFF. Turn ON the Tech 2(R). Press ENTER at the Title screen. Turn ignition switch to RUN position, engine OFF. Select SERVICE PROGRAMMING SYSTEM. Select the PROGRAM ECU function on the Tech 2(R). Verify the VIN and calibration numbers, select CONTINUE. Follow the on-screen instructions and select Continue. Select CONTINUE and exit the program after the Tech 2(R) displays PROGRAMMING WAS SUCCESSFUL.
11. Turn ignition switch to OFF position.
12. Turn OFF the Tech 2(R).
13. Disconnect the Tech 2(R) from the vehicle.

Scheme 1

Scheme 2

Verifying Reprogramming

Note. Some vehicles will require that Idle Learn, TP Learn, Theft Deterrent Relearn, or Crankshaft Variation Learn procedures be performed after programming. Consult the appropriate service information for these procedures.

Verify the PCM programming was successful using the following procedure

1. Turn OFF the ignition for 30 seconds.
2. Start the engine.
3. Repeat the SPS procedure if the vehicle does not start or starts but runs rough.

SERVICE PROGRAMMING SYSTEM PASS-THRU PROCEDURE

Note. The TIS supports service programming with the Tech 2(R) scan tool only.

Note. The Off-Board Programming Adapter Kit (J 41207-C) is required when a module must be programmed without having the vehicle present. The adapter allows the module to be turned ON and communicate with the Tech 2(R).

For additional SPS information, refer to POWERTRAIN CONTROL MODULE description.

Performing Pass-Thru Procedure

1. Launch the TIS application at the terminal.
2. Select the SERVICE PROGRAMMING SYSTEM.
3. Highlight the following information on the Select DIAGNOSTIC TOOL PROGRAMMING PROCESS screen: Select Diagnostic Tool - Select PASS-THRU. Select Programming - Identify whether an existing module is being reprogrammed or a module is being replaced with a new one. Select ECU Location - Select vehicle.
4. Select NEXT.
5. Complete all terminal-directed data on the PREPARING FOR COMMUNICATION/DETERMINE VEHICLE screen until NEXT is highlighted.
6. Select NEXT.
7. Follow the on-screen instructions for connecting the control module, the Off-Board Programming Adapter (OBPA). Refer to the TIS Users Guide for a listing of OBPA, or the Tech 2(R).
8. Select NEXT.
9. Pass-Thru displays the VIN stored in the control module. If a new control module is being programmed, enter the correct VIN of the vehicle.
10. Select NEXT.
11. Select the appropriate options if the Options screen appears.
12. Select Next.
13. Select the type of programming to be performed from the following categories: Normal - Used for updating an existing calibration or programming a new controller. Vehicle Configuration Index - Used for updating an existing controller or programming a new controller for newer vehicles whose VINs are not yet in the database. Reconfigure - Used to reconfigure a vehicle for changes in tire size and axle ratios.
14. Select Next.
15. Select a calibration selection on the Calibration Selection screen, if necessary.
16. Ensure all the desired calibration folder tabs have a Green check mark.
17. Select NEXT.
18. Verify the current and selected calibration of the control module on the Summary screen.
19. Select NEXT.
20. Select OK.
21. Complete all of the terminal-directed data on the Programming Complete screen.
22. Select OK.
23. Select CLOSE.
24. Turn OFF the OBPA.
25. Turn OFF the scan tool.
26. Disconnect the OBPA from the Tech 2(R) and the control module.

SERVICE PROGRAMMING SYSTEM OFF BOARD REMOTE PROCEDURE

Note. Ensure the Tech 2(R) and the terminal are both equipped with the latest software before performing SPS.

The Off-Board Programming Adapter Kit (J 41207-C) is required when a module must be programmed without having the vehicle present. The adapter allows the module to be turned ON and communicate with the scan tool.

For additional SPS information, refer to POWERTRAIN CONTROL MODULE description.

Performing Off Board Remote Procedure

1. Obtain the Vehicle Identification Number (VIN) of the vehicle for which the module is being programmed.
2. Launch the TIS application at the terminal.
3. Select the SERVICE PROGRAMMING SYSTEM.
4. Highlight the following information on the Select Diagnostic Tool and Programming Process screen: Select Diagnostic Tool - Select Tech 2(R). Select Programming Process - Identify whether an existing module is being reprogrammed or replaced with a new one. Select ECU location - Select Off-Board Programming Adapter.
5. Select NEXT.
6. Follow the directions on the Preparing for Communication screen for connecting the following components: The PCM. The Off-Board Programming Adapter (OBPA). Refer to the TIS users guide for a listing of the OBPA. The Tech 2(R). (Scheme 3)
7. Select the SERVICE PROGRAMMING REQUEST INFORMATION function on the Tech 2(R).
8. Follow the Tech 2(R) instructions to obtain the module data and security information.
9. After the Tech 2(R) has received the data from the module, exit the REQUEST INFO mode.
10. Disconnect the Tech 2(R) from the OBPA.
11. Turn OFF the Tech 2(R).
12. Connect the Tech 2(R) to the terminal. (Scheme 2)
13. Turn ON the Tech 2(R).
14. Select NEXT at the terminal after the Tech 2(R) start-up screen appears.
15. Enter the VIN of the vehicle that will be receiving the NEW PCM.
16. Select NEXT.
17. Select the type of programming to be performed from the following categories: Normal - Used for updating an existing calibration or programming a new controller. Vehicle Configuration Index - Used for updating an existing controller or programming a new controller for newer vehicles whose VINs are not yet in the database. Reconfigure - Used to reconfigure a vehicle for changes in tire size and axle ratios.
18. Select NEXT.
19. Select a calibration on the CALIBRATION SELECTION screen, if necessary.
20. Ensure all the desired folder tabs have a Green check mark.
21. Select NEXT.
22. Verify the current and the selected calibration of the PCM on the summary screen.
23. Select NEXT.
24. Select OK.
25. On model year 1996 and newer controllers, a crankshaft position (CKP) relearn procedure box may appear. Select OK.
26. Follow the on-screen instructions, if any, when the PROGRAM CONTROLLER/PROGRAMMING COMPLETE screen appears.
27. Select CLOSE.
28. Turn OFF the Tech 2(R).
29. Disconnect the Tech 2(R) from the terminal.
30. Connect the Tech 2(R) to the OBPA.
31. Turn ON the Tech 2(R).
32. Select ENTER at the title screen.
33. Select the SERVICE PROGRAMMING SYSTEM at the Main Menu.
34. Select the Program ECU function.
35. Select CONTINUE.
36. Follow the on-screen instructions.
37. Select CONTINUE.
38. Select EXIT when the programming is complete.
39. Turn OFF the OBPA.
40. Turn OFF the Tech 2(R).
41. Wait 30 seconds after the OBPA is turned OFF before disconnecting the PCM. Disconnect the OBPA from the Tech 2(R) and the PCM.

Scheme 3

SERVICE PROGRAMMING SYSTEM OFF BOARD PASS-THRU PROCEDURE

Note. The TIS supports service programming with the Tech 2(R) scan tool only.

Note. Ensure the Tech 2(R) and the terminal are both equipped with the latest software before performing SPS.

Pass-Thru programming allows the scan tool to remain connected to the terminal and to the vehicle throughout the programming process. The vehicle must be in close proximity to the terminal while using Pass-Thru.

Performing Off Board Pass-Thru Procedure

1. Launch the TIS application in the terminal.
2. Select the SERVICE PROGRAMMING SYSTEM.
3. Highlight the following information on the Select Diagnostic Tool and Programming Process Screen: Select Diagnostic Tool - Select PASS-THRU. Select Programming Process - Identify whether an existing module is being reprogrammed, or a module is being replaced with a new one. Select ECU location - Select vehicle.
4. Select NEXT.
5. Complete all terminal-directed data at the PREPARING FOR COMMUNICATION/DETERMINE VEHICLE screen until NEXT is highlighted. (Scheme 3)
6. Select NEXT.
7. Follow the instructions on the PREPARING FOR COMMUNICATION screen.
8. Select NEXT.
9. Verify the VIN on the VALIDATE VEHICLE IDENTIFICATION NUMBER screen.
10. Select NEXT.
11. If an option screen appears, verify the vehicle configuration and/or RPO information.
12. Select NEXT.
13. Highlight the appropriate control module and programming type on the SUPPORTED CONTROLLERS screen.
14. Select NEXT.
15. Select a calibration selection on the CALIBRATION SELECTION screen, if necessary.
16. Ensure all the desired calibration folder tabs have a Green check mark.
17. Select NEXT.
18. Verify the current calibrations with the selected calibrations.
19. Select NEXT.
20. The Transfer Data screen will appear until the progress bar reaches 100 percent. This may take up to 30 minutes.
21. Complete all of the terminal-directed data on the PROGRAMMING COMPLETE screen.
22. Turn OFF the Tech 2(R).
23. Disconnect the Tech 2(R) from the vehicle.

CKP SYSTEM VARIATION LEARN PROCEDURE

Note. For additional diagnostic information, refer to DTC P1336: CRANKSHAFT POSITION SYSTEM VARIATION NOT LEARNED under DIAGNOSTIC TESTS.

1. Connect scan tool to DLC.
2. Monitor the Powertrain Control Module (PCM) for DTCs. If other DTCs are set, except DTCs P1336, refer to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) for the applicable DTC that set.
3. Using a scan tool, select the CRANKSHAFT POSITION VARIATION LEARN procedure.
4. Observe the fuel cut-off specifications for the engine that you are performing the learn procedure on.
5. The scan tool instructs you to perform the following: Block the drive wheels. Apply the vehicles parking brake. Cycle the ignition switch from OFF to RUN position. Apply and hold the brake pedal. Start and idle the engine. Place the vehicle's automatic transmission in Park, or the manual transmission in Neutral. The scan tool monitors certain component signals to determine if all the conditions are met to continue with the procedure. The scan tool only displays the condition that inhibits the procedure. The scan tool monitors the following components: CKP sensors activity - If there is a CKP sensor condition, refer to the applicable DTC that set. Camshaft Position Sensor activity - If there is a Camshaft Position Sensor (CMP) sensor condition, refer to the applicable DTC that set. Engine Coolant Temperature - If the Engine Coolant Temperature (ECT) is not warm enough, idle the engine until the ECT reaches the correct temperature.
6. Enable the crankshaft position system variation learn procedure using the scan tool.
7. Slowly increase the engine speed to the RPM that you observed.
8. Immediately release the throttle when fuel cut-off is reached.
9. The scan tool displays LEARN STATUS: LEARNED THIS IGNITION. If the scan tool does NOT display this message and no additional DTCs set, go to appropriate article in ENGINES. If a DTC set, refer to Diagnostic Trouble Code (DTC) List for the applicable DTC that set. If any other DTCs set, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) for the applicable DTC that set.
10. Turn ignition switch to OFF position for 30 seconds after the learn procedure is completed successfully.

PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS

Note. Due to component variability, the Vehicle Theft Deterrent (VTD) system must have the learn procedure performed regardless, if vehicle starts on the first ignition cycle after a VTD repair. All codes in the theft deterrent module must be cleared for a relearn.

Note. The BCM must be programmed with proper RPO configurations before performing learn procedures. If replacing BCM with a GM Service Parts Operations (SPO) replacement part, the module will learn Passlock(R) sensor data code immediately. The existing PCM however, must learn the new fuel continue password when BCM is replaced.

Note. If replacing a PCM with a replacement part, after programming, these modules will learn incoming fuel continue password immediately upon receipt of a password message. Once a password message is received and a password is learned, a learn procedure must be performed to change this password again. A PCM which has been previously installed in another vehicle will have learned the other vehicle's fuel continue password and will require a learn procedure after programming to learn current vehicle's password.

Use these procedures after replacing

1. The BCM.
2. The PCM.

10 Minute Learn Procedure

1. Connect the Tech 2(R) to the vehicle.
2. Select REQUEST INFORMATION under SERVICE PROGRAMMING.
3. Disconnect the Tech 2(R) from the vehicle and connect it to a Techline terminal.
4. On the Techline terminal, select THEFT MODULE RE-LEARN under SERVICE PROGRAMMING.
5. Disconnect the Tech 2(R) from the Techline terminal and connect it to the vehicle.
6. Turn ignition switch to RUN position, engine OFF.
7. Select VTD RE-LEARN under SERVICE PROGRAMMING.
8. Attempt to start the engine, then release the key to RUN position (vehicle will not start).
9. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF (the vehicle is now ready to relearn the password on the next ignition switch transition from OFF to CRANK position).
10. Turn ignition switch to OFF position, and wait 5 seconds.
11. Start the engine (the vehicle has now learned the password).
12. Using the Tech 2(R) (scan tool), clear any DTCs.

30 Minute Learn Procedure

1. Turn ignition switch to RUN position, engine OFF.
2. Attempt to start the engine, then release the key to RUN position (vehicle will not start).
3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
4. Turn ignition switch to OFF position, and wait 5 seconds.
5. Repeat steps 1 - 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the password on the next ignition switch transition from OFF to CRANK position).
6. Start the engine (the vehicle has now learned the password).
7. Using a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles).

DRIVE CYCLES

See INSPECTION/MAINTENANCE SYSTEM CHECK .

Several states require that a vehicle pass On-Board Diagnostic (OBD) system tests and I/M emission inspection in order to renew license plates. This is accomplished by viewing the I/M SYSTEM STATUS display on scan tool. Using a scan tool, the technician can observe the I/M system Status to verify that vehicle meets the criteria that complies with the local area requirements.

Conditions For Updating I/M system Status

Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a Diagnostic Trouble Code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or any one of the DTCs comprising the monitor have illuminated the MIL. Once all of the tests are completed, the I/M system Status display will indicate YES in the completed column. For example, when the HO2S Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has four heated oxygen sensors, all four heater circuits have been diagnosed. The I/M system Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M system Status indicator to NO

1. The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
2. The battery has been disconnected or discharged below operating voltage.
3. The Powertrain Control Module (PCM) power or ground has been interrupted.
4. The PCM has been reprogrammed.
5. The PCM DTCs have been cleared as part of a service procedure.

Monitored Emission Control Systems

The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with Secondary Air Injection (AIR) or Exhaust Gas Recirculation (EGR). The OBD II regulations require monitoring of the following

1. Air conditioning system.
2. Catalytic converter efficiency.
3. Comprehensive component monitoring. Emission related inputs and outputs.
4. Evaporative Emissions (EVAP) system.
5. Exhaust Gas Recirculation (EGR) system.
6. Fuel delivery system.
7. Heated catalyst monitoring.
8. Misfire monitoring.
9. Oxygen Sensor or Heated Oxygen Sensor (O2S or HO2S) system.
10. Oxygen Sensor Heater (HO2S Heater) system.
11. Secondary Air Injection (AIR) system.

For the specific DTCs required for each system, refer to INSPECTION/MAINTENANCE SYSTEM DTCS . Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously on some vehicles and may not require an indicator.

1. 1 - Any DTCs set, even those that are not listed in the Inspection/Maintenance System DTCs, may prevent the required DTCs from running. If there is any question as to whether a set DTC is disabling the required I/M diagnostic, review the Conditions for Running in the diagnostic procedures for the DTC required by the I/M diagnostic. A list of disabling DTCs, if applicable, is contained in the supporting text for that DTC.
2. 2 - Anytime a PCM is reprogrammed or the diagnostic trouble codes are cleared as part of a repair procedure, all the I/M system Status indicators will reset to NO.
3. 3 - Use discretion when determining whether the entire system set procedure needs to be performed. For example, if the only tests that have not run are those that require the engine to be at operating temperature, then only those individual tests need to be run. There is no need to allow the engine to completely cool to run these tests.

Note. Many DTC related repairs will instruct the technician to clear the DTC information. This procedure will reset ALL of the I/M system Status indicators to NO, and require performing the I/M Complete System Set Procedure.

1. Perform powertrain diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. Repair any DTCs or driveability concerns that would prevent the I/M system Status tests from completing. Did you find and repair a DTC or driveability concern? If yes, go to step 3 . If no, go to next step.
2. Review any service bulletins for software updates that may prevent I/M readiness. Perform any reprogramming or repairs indicated by the service bulletins. Was a repair service required? If yes, go to «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go next step.
3. Using scan tool, observe the I/M system Status display. Is more than one test indicating a NO status? If yes, go to «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go to appropriate INSPECTION/MAINTENANCE SYSTEM SET procedure for the indicated system.

Diagnostic Aids

The I/M system Status display provides an indication of when the Powertrain Control Module (PCM) has completed the required tests. This does not necessarily mean that the test has passed, only that a decision was made. If the diagnostic fails, a DTC will indicate the failure. If a failure indication is present for a DTC associated with one of the I/M regulated systems, it may prevent other required tests from running. For example, a DTC for the control circuit of the relay controlling an AIR pump may not be listed in the I/M system DTC table because it is a continuous test. If this DTC is set, the Active Tests for the AIR system may not run.

The I/M system status information may be useful for a technician to determine if diagnostics have run when verifying repairs.

The purpose of the I/M Complete System Set Procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics, and complete the trips for those particular diagnostics. When all diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform this test when more than one or all of the I/M System Status indicators are set to NO.

Conditions For Running Test (Cold Start)

Ensure vehicle meets the following conditions before performing procedure

1. Barometric pressure is greater than 65 kPa.
2. The ECT sensor parameter is less than 86°F (30°C).
3. The IAT sensor parameter is less than 90°F (32°C).
4. The difference between IAT and ECT is 7°F or less.
5. Battery voltage is 10-18 volts.
6. Fuel level is 1/4-3/4.

Test will initiate only after a cold start. A cold start is considered when engine coolant temperature is less than 35°F (2°C).

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 - Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - This step runs the HO2S heater tests and initiate the EVAP system test. Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria. The PCM considers the engine to be cold if the following conditions are met: ECT sensor parameter is less than 86°F (30°C). The start-up ECT and IAT are within 16°F (9°C) of each other.
3. 3 - This step runs the EVAP, AIR and the oxygen sensor tests. The EVAP test begins once the engine coolant reaches a calibrated temperature. The AIR Test, if equipped, begins shortly after closed loop and the indicated speed is achieved. The oxygen sensor tests begin once the engine is at operating temperature, in closed loop fuel control, and a calibrated amount of time has elapsed.
4. 4 - This step is to run the Exhaust Gas Recirculation (EGR) tests. The EGR Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required to maintain a high, steady Manifold Absolute Pressure (MAP) signal.
5. 5 - This step runs the catalyst tests. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.
6. 6 - Perform the individual system test for any of the systems that do not update to YES.
7. 7 - The I/M system status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

1. Did you perform the Inspection/Maintenance (I/M) system check? If yes, go to next step. If no, go to «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
2. Preprogram the scan tool with the vehicle information before the ignition switch is turned to RUN position. Ensure the vehicle is within the Conditions for Running Test (Cold Start). See «CONDITIONS FOR RUNNING TEST (COLD START)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__conditions-for-running-test-cold-start) . Turn OFF all accessories, e.g., A/C, blower fan, etc. Set vehicle parking brake. Verify the transmission is in Park (A/T) or Neutral (M/T). Start the engine and allow engine to idle for 2 minutes. When complete, go to next step.
3. In order for the next group of tests to run, the vehicle must operate in the following conditions: Accelerate at part throttle to 55 MPH. Maintain this speed without changing throttle position for 8-10 minutes until engine reaches operating temperature. Continue operating under these conditions for additional 6 minutes. When complete, go to next step.
4. In order for this test to run, the vehicle must operate in the following conditions: The vehicle speed is reduced to 45 MPH with this speed maintained for one additional minute. Four decelerations of 25 seconds each from 45 MPH while the throttle is closed, no brake application on either manual or automatic transmissions, no clutch actuation (M/T), no manual downshifts, and vehicle speed remains greater than 25 MPH. After each deceleration period, vehicle is returned to 45 MPH under part throttle acceleration and speed is maintained for 15 seconds. When complete, go to next step.
5. In order for the next group of tests to run, the vehicle must operate in the following conditions: Accelerate at part throttle to 45-55 MPH and maintain this speed for 2 minutes, then decelerate to zero MPH. With engine idling for 2 minutes, the following criteria should be maintained: Service brake depressed, transmission in Drive (A/T) or Neutral (M/T) with clutch pedal depressed. When complete, go to next step.
6. Using a scan tool, observe the I/M system Status display. Did all of the I/M system Status indicators update to YES? If yes, go to next step. If no, go to the I/M system Set Procedure for the indicated systems.
7. Using scan tool, observe emission related DTC portion of I/M system status display. Does the scan tool indicate any emission related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures may prevent tests such as Heated Oxygen Sensor (HO2S) heater and Evaporative Emission (EVAP) system from initiating. If a step is interrupted before completion, perform the remaining portion of the set procedures. Any portion of the set procedure that requires the engine at operating temperature may be repeated. This allows most of the diagnostics to run and the remaining tests can be performed using the individual System Set Procedures.

If the vehicle has recently run, start this procedure at step 3 . This will allow the tests that require the engine at operating temperature to run. Using this method allows shorter cool down periods if the tests requiring a cold start do not initiate.

The scan tool can be used to monitor each of the I/M system status indicators during the I/M complete system set procedure. When all of the indicators for a test step have updated to YES, testing can move on to the next step even if the remaining portion of the test is not complete. For example, step 3 is designed to run EVAP, Secondary Air Injection (AIR), and HO2S tests. The procedure instructs the technician to operate the vehicle in the enable conditions for 6 minutes. If the test updates to YES within 4 minutes, it is not necessary to continue with the enable conditions and testing can advance to the next step.

INSPECTION/MAINTENANCE SYSTEM DTCS

Note. Not all vehicles will have every DTC listed in each section. For example, a vehicle may have only 2 oxygen sensors or 1 catalyst. Only those DTCs applicable to the vehicle are required to update each System Status to YES. Refer to the appropriate service manual to determine which DTCs are supported for each vehicle.

The following DTCs are required to set system status to YES

AIR - Secondary Air Injection (AIR) System

Catalyst System

1. P0420: Catalyst System - Low Efficiency.

EGR

1. DTC P0401: EGR Flow Insufficient
2. DTC P0404: EGR Open Position Performance
3. DTC P0405: EGR Position Sensor Circuit - Low Voltage
4. DTC P1404: EGR Closed Position Performance

EVAP System

1. P0440: Evaporative Emission System
2. P0442: Evaporative Emission Control System - Small Leak Detected
3. P0446: EVAP Vent System Performance
4. P1441: Evaporative Emission System Flow During Non-Purge

Oxygen Sensor

1. P0133: HO2S 1 - Slow Response
2. P0140: HO2S 2 Circuit - Insufficient Activity
3. P1133: HO2S 1 - Insufficient Switching
4. P1134: HO2S 1 Transition Time Ratio

Oxygen Sensor Heater

1. P0135: HO2S 1 - Heater Performance
2. P0141: HO2S 2 - Heater Performance

Diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .

This test satisfies the enable criteria necessary to execute I/M readiness diagnostics for the catalyst system. The test may be used to set the I/M System Status indicators to YES. Ensure that the vehicle meets the requirements listed in Conditions For Running Test before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

Conditions For Running Test

1. Barometric Pressure (BARO) sensor parameter is more than 65 kPa.
2. Engine Coolant Temperature (ECT) sensor parameter is 202-212°F (94-100°C).
3. Intake Air Temperature (IAT) sensor parameter is 59-167°F (15-75°C).
4. Engine is in closed loop fuel control.
5. Engine has run 6-8 minutes off idle to initiate test.
6. Battery voltage is 10-18 volts.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 1 - Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - The catalyst test during the idle period immediately following the cruise period.
3. 3 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. Refer to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. 4 - This step identifies any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions For Running Test.
5. 5 - The I/M System Status only verifies whether a diagnostic has run, not the outcome of the test. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . After performing I/M system check, go to next step.
2. Ensure that the vehicle is within the Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__conditions-for-running-test) . Turn all of the accessories OFF, such as the A/C, blower fan, etc. Start the engine and allow to idle. In order for this test to run, the vehicle must operate in the following conditions: Accelerate at part throttle to 55 MPH and maintain speed for 5 minutes. Decelerate to a stop. Allow engine to idle for 2 minutes with service brake applied, A/T in Drive or M/T in Neutral with clutch depressed. Using scan tool, monitor I/M SYSTEM STATUS. Did the Catalyst System Status update to YES? If yes, go to step 5 . If no, go to next step.
3. Using scan tool, observe DTC information. Does scan tool indicate any failed DTCs? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
4. Refer to Inspection/Maintenance (I/M) System DTCs to determine which DTCs are required to run to complete this test. See «INSPECTION/MAINTENANCE SYSTEM DTCS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__inspectionmaintenance-system-dtcs) . Use scan tool to observe the NOT RAN SINCE CODE CLEARED display. Determine which of DTCs required for a YES status has not run. Enter DTC number in the Specific DTC menu of scan tool. Operate vehicle within Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__conditions-for-running-test) . Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Use a scan tool to observe the I/M System Status display. Did the CATALYST SYSTEM STATUS update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Use a scan tool to observe the Emission Related DTC portion of the I/M System Status display. Does the scan tool indicate any emission related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The Powertrain Control Module (PCM) runs a maximum of 6 tests per trip until the Catalyst System Status updates to YES. If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the Malfunction Indicator Light (MIL) is requested. The I/M System Status also registers the number of Diagnostic Trouble Codes (DTCs).

The first failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met for the test to run again. These conditions may include a partial to complete engine cool down. The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning ON, may cause the test to abort. If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

This test satisfies the enable criteria necessary to execute I/M readiness diagnostics for the Exhaust Gas Recirculation (EGR) system. The test may be used to set the I/M System Status indicators to YES. Ensure that the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

Conditions for Running

1. The Barometric Pressure (BARO) sensor parameter is more than 65 kPa.
2. The engine coolant is at operating temperature, 176-230°F (80-110°C).
3. The Intake Air Temperature (IAT) is less than 149°F (65°C).

The numbers below refer to the step numbers in the diagnostic procedure.

1. 1 - Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - The EGR Active Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required to maintain a high, steady MAP signal.
3. 3 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. 4 - This step helps identify any unique or any unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . After performing I/M system check, go to next step.
2. Ensure that the vehicle is within the Conditions for Running Test. See «CONDITIONS FOR RUNNING»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__conditions-for-running) . Turn all of the accessories OFF, such as the A/C, blower fan, etc. Start the engine and allow to idle. In order for this test to run, the vehicle must operate in the following conditions: Accelerate at part throttle to 45 MPH and maintain speed for one minute. Four decelerations of 25 seconds each from 45 MPH while the throttle is closed, NO brake application, NO manual downshift, vehicle speed remains above 25 MPH. After each deceleration period, vehicle is returned to 45 MPH under part throttle acceleration and speed is maintained for 15 seconds. Using scan tool, monitor I/M SYSTEM STATUS. Did the EGR System Status update to YES? If yes, go to step 5 . If no, go to next step.
3. Using a scan tool, observe the DTC Information. Does the scan tool indicate any failed DTCs? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
4. Refer to the Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run to complete this test. See «INSPECTION/MAINTENANCE SYSTEM DTCS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__inspectionmaintenance-system-dtcs) . Using a scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the SPECIFIC DTC menu of the scan tool. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC. Repeat the procedure until the scan tool indicates the diagnostic test has run. Repeat procedure for any additional required DTCs that have not run. Using a scan tool, observe the I/M System Status display. Did the EGR System Status update to YES? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Using a scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does the scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The Powertrain Control Module (PCM) only runs the EGR Active Tests during a gradual deceleration with a closed throttle and a vehicle speed above 25 MPH. Several deceleration cycles may be necessary to accumulate a sufficient number of EGR flow samples. The procedure outlined in the test is for a clear, flat road. If the procedure is performed on a road with a slight down hill grade, the test may acquire the necessary sample counters in one or two decel trips. If the test is interrupted during the procedure, completing the test may take more than three deceleration cycles. If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M System Status updates to YES. If a test for a specific system has failed, the I/M System Status updates to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display indicates the Malfunction Indicator Light (MIL) is requested. The I/M System Status also registers the number of DTCs.

The first failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met for the test to run again. These conditions may include a partial to complete engine cool down. The I/M System Status updates only when the DTC fails the second time, or all of the tests pass.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort. If a diagnostic test is difficult to run, observe the I/M System Status display while maintaining the necessary enable conditions until the system status updates to YES.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Evaporative Emission (EVAP) system. The test may be used to set the I/M System Status indicators to YES. Service Bay Tests are included on the scan tool for some systems depending upon vehicle make and model. The test is designed to allow the EVAP Diagnostic Tests to run in service bay conditions. Ensure the vehicle meets the requirements listed in Conditions for Running before performing either EVAP System Test. Failure to meet the necessary requirements may produce inaccurate test results.

Note. This is for non scan tool Service Bay Test equipped vehicles.

1. Barometric Pressure (BARO) sensor parameter is greater than 65 kPa.
2. The Engine Coolant Temperature (ECT) sensor parameter is 158°F (70°C).
3. The fuel level is 1/4-3/4.
4. The battery voltage is 10-18 volts.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 - Perform the I/M system check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - This step determines whether or not the EVAP System Test has passed. If the system is operating correctly, the scan tool indicates that the system has passed and the I/M System Status updates to YES. If the EVAP Service Bay Test aborts because of lost enable conditions, the test can be repeated once the enable criteria is met.
3. 4 - A failed DTC during the EVAP Service Bay Test may not appear in the DTC Information display on some vehicles. The Service Bay Test displays an indication of which test failed as a directive to the appropriate service information. Some vehicles will display the test as aborted and the first failure of type "B" DTC appears in the DTC Information.
4. 5 - The EVAP System Test usually begins around an ECT of 176°F (80°C). The vehicle should be operated moderately until this temperature is reached. The engine coolant temperature can be monitored using a scan tool.
5. 6 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. Go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
6. 7 - This step helps identify any unique or any unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
7. 8 - The I/M system Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

1. Did you perform the Inspection/Maintenance (I/M) system check? If yes, go to next step. If no, go to «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
2. Using a scan tool, select SPECIAL FUNCTIONS. Determine if the vehicle is equipped with a SERVICE BAY TEST for the EVAP system. Is the vehicle equipped with EVAP Service Bay Test? If yes, go to next step. If no, go to step 5 .
3. Ensure that the vehicle is within the Conditions for Running. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Turn OFF all of the accessories, such as A/C, blower fan, etc. Following the directions on the scan tool, perform the EVAP SERVICE BAY TEST. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the EVAP system pass the Service Bay Test? If yes, go to step 8 . If no, go to next step.
4. Observe the scan tool Service Bay Test for an indication of why the test did not pass, e.g., failed DTC, test aborted, etc. Refer to the appropriate service information for diagnosis and repair of the condition as necessary. After repairs, «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Ensure vehicle is within the Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Turn all accessories OFF, e.g., A/C, blower fan, etc. Start the engine and let idle. Accelerate at part throttle to 45 MPH and maintained speed until engine reaches operating temperature. This may be up to 8-10 minutes depending on the start up coolant temperature. Continue the operating conditions for an additional 3 minutes after the engine reaches operating temperature, or until the I/M System Status indicator updates to YES. Decelerate to zero MPH. Operate engine at idle for 2 minutes. Did the EVAP System Status update to YES? If yes, go to step 8 . If no, go to next step.
6. Using a scan tool, observe the DTC Information. Does the scan tool indicate any failed DTCs? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
7. Determine which DTCs are required to run to complete this test. See «INSPECTION/MAINTENANCE SYSTEM DTCS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__inspectionmaintenance-system-dtcs) . Using a scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the SPECIFIC DTC menu of the scan tool. Operate the vehicle within the Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Repeat the procedure until the scan tool indicates the diagnostic test has run. Repeat procedure for any additional required DTCs that have not run. Using a scan tool, observe the I/M System Status display. Did the EVAP System Status update to YES? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
8. Using a scan tool, observe the emission related DTC portion of the I/M System Status display. Does the scan tool indicate any emission related DTCs set? If yes, «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

Extreme high or low ambient temperatures may prevent EVAP system tests from initializing. Performing a visual inspection prior to running test may prevent having to repeat test. A loose fuel cap may cause test to abort or fail and prevent I/M system from updating. A failed or aborted test will require vehicle to cool down to meet enable criteria to run another test.

I/M system status does not indicate whether test has passed or failed, only that test has run. When all diagnostics for a specific system have run and passed, I/M system status will update to YES. If a test for a specific system has failed, I/M system status will update to YES, indicating a determination was made, even if all required tests have not run. When a failure occurs, DTC portion of the I/M system status display will indicate MIL is requested. I/M system status also registers number of DTCs.

First failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update I/M system status to YES. A second trip is required, and all conditions to run must be met for test to run again. These conditions may include a partial to complete engine cool down. I/M system status will update only when DTC fails second time, or all tests pass.

If there is an impending failure, system may require more time to run diagnostic than was allotted in set procedure. If test does not run after numerous attempts and no DTC is set, review appropriate scan tool data list and service information for an indication of why test does not complete. Some tests may abort due to changes in conditions while the is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning on, may cause test to abort.

If a diagnostic test is difficult to run, observe I/M system status display while maintaining necessary enable conditions until system status updates to YES.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Oxygen Sensor/Heated Oxygen Sensor (O2S/HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

1. The ECT sensor parameter is more than 176°F (80°C).
2. Engine is in closed loop fuel control.
3. Engine has been running more than 4 minutes.
4. Battery voltage is 10-18 volts.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 1 - Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - The oxygen sensor tests begin shortly after the indicated speed is achieved. The engine RPM may be too low in overdrive on manual transmission vehicles. If difficulty is encountered updating the status, operate the vehicle in the recommended gear during the test.
3. 3 - This step is to identify a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. 4 - This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions For Running Test.
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . After performing I/M system check, go to next step.
2. Ensure the vehicle is within the Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Turn all of the accessories OFF, e.g., A/C, blower fan, etc. Start the engine and allow to idle. In order for this test to run, the vehicle must operate in the following conditions: Accelerate at part throttle to 45-55 MPH with this speed maintained for 6 minutes or until the I/M System Status updates to YES. Manual transmissions, either 5 or 6 speed, may require operation in 4th or 5th gear respectively, for this test to run. Using a scan tool, review the I/M System Status display. Did the HO2S/O2S System Status update to YES? If yes, go to step 5 . If no, go to next step.
3. Using scan tool, observe DTC information. If scan tool indicates any failed DTCs, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If scan tool does not indicate any failed DTCs, go to next step.
4. Determine which DTCs are required to run to complete this test. See «INSPECTION/MAINTENANCE SYSTEM DTCS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__inspectionmaintenance-system-dtcs) . Using a scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter DTC number in the Specific DTC menu of scan tool. Operate vehicle within the Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Using scan tool, observe the I/M System Status display. Did the HO2S/O2S System Status update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Using a scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does the scan tool indicate any emission related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

If status does not update, test outlined in this procedure can be repeated until I/M SYSTEM STATUS updates to YES.

I/M SYSTEM STATUS does not indicate whether test has passed or failed, only that test was run. When all diagnostics for a specific system have run and passed, I/M SYSTEM STATUS will update to YES. If a test for a specific system has failed, I/M SYSTEM STATUS will update to YES, indicating a determination was made, even if all required tests have not run. When a failure occurs, DTC portion of the I/M system status display will indicate MIL is requested. I/M system status also registers number of DTCs.

First failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update I/M SYSTEM STATUS to YES. A second trip is required, and all conditions to run must be met for test to run again. These conditions may include a partial to complete engine cool down.

I/M SYSTEM STATUS will update only when DTC fails second time, or all tests pass.

If there is an impending failure, system may require more time to run diagnostic than was allotted in set procedure. If test does not run after numerous attempts and no DTC is set, review appropriate scan tool data list and service information for an indication of why test does not complete. Some tests may abort due to changes in the conditions while test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning on, may cause test to abort.

If a diagnostic test is difficult to run, observe I/M SYSTEM STATUS display while maintaining necessary enable conditions until system status updates to YES.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Heated Oxygen Sensor (HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions For Running Test before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

1. The Engine Coolant Temperature (ECT) sensor parameter is less than 113°F (45°C).
2. The Intake Air Temperature (IAT) sensor parameter is less than 113°F (45°C).
3. Difference between ECT and IAT is less than 13°F (11°C).
4. Battery voltage is 11.6-16.0 volts.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 1 - Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.
3. 3 - This step is to identify a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. Refer to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. 4 - This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions For Running Test.
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . After performing I/M system check, go to next step.
2. Pre-program scan tool with vehicle information before ignition switch is turned to RUN position. Ensure vehicle is within enable criteria. Set vehicle parking brake. Verify transmission is in Park for A/T and Neutral for M/T. Turn OFF all accessories. Start the engine and allow it to idle for 2 minutes or until I/M SYSTEM STATUS indicator updates to YES. If HO2S HEATER SYSTEM STATUS updates to YES, go to step 5 . If HO2S HEATER SYSTEM STATUS does not update to YES, go to next step.
3. Using scan tool, observe DTC information. If scan tool indicates any failed DTCs, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If scan tool does not indicate any failed DTCs, go to next step.
4. Determine which DTCs are required to run to complete this test. See «INSPECTION/MAINTENANCE SYSTEM DTCS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__inspectionmaintenance-system-dtcs) . Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the SPECIFIC DTC menu of the scan tool. Operate vehicle within the Conditions for Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Repeat the procedure until the scan tool indicates the diagnostic test has run. Repeat this procedure for any additional required DTCs that have not run. Using scan tool, observe the I/M System Status display. Did the HO2S Heater System Status update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Using scan tool, check for DTCs. If scan tool indicates any DTCs are set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no DTCs are set, system is okay at this time.

The HO2S Heater Tests will normally run within the 2 minutes allotted in the procedure. If there is an indeterminate condition, the test may take up to 8 minutes on some vehicles before a decision of pass or fail is made. If the test does not update within the allotted period of time, continue operation within the enable conditions until the test updates to YES. If the test does not update to YES, the test may have failed or aborted due to the loss of enabling conditions. Extremely high ambient temperatures may prevent the HO2S Heater Test from initiating.

I/M SYSTEM STATUS does not indicate whether test has passed or failed, only that test was run. When all diagnostics for a specific system have run and passed, I/M SYSTEM STATUS will update to YES. If a test for a specific system has failed, I/M SYSTEM STATUS will update to YES, indicating a determination was made, even if all required tests have not run. When a failure occurs, DTC portion of the I/M system status display will indicate MIL is requested. I/M system status also registers number of DTCs.

First failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update I/M SYSTEM STATUS to YES. A second trip is required, and all conditions to run must be met for test to run again. These conditions may include a partial to complete engine cool down.

The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning ON, may cause the test to abort.

If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

The Evaporative Emission (EVAP) Service Bay Test raises the Engine Coolant Temperature (ECT) threshold so that the temperature sensitive EVAP diagnosis tests can run while in service environments. When the EVAP tests are run the service bay test will indicate a pass or will indicate a specific DTC has failed. The EVAP service bay test can be used to verify an existing condition and verify that the EVAP system is OK after a repair is completed.

The following conditions must be met to enable the Service Bay Test

1. The ignition switch is in RUN position.
2. The battery voltage is 9-18 volts.
3. The Engine Coolant Temperature (ECT) sensor parameter is less than 158°F (70°C).
4. The fuel level is 15-85 percent of capacity.
5. The vehicle speed is less than 3 MPH.
6. Stored DTCs have been cleared.

Test Procedure

1. Connect scan tool.
2. Using a scan tool, select SERVICE BAY TEST in the SPECIAL FUNCTIONS menu.
3. Follow the instructions on the scan tool.
4. Check DTCs using a scan tool.
5. Continue with the published service manual diagnostic DTC procedure.

SUMMARY

If no Diagnostic Trouble Codes (DTC) are present and a no-start condition exists, go to NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no DTCs are present and a driveability condition exists, go to TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

DIAGNOSTIC TROUBLE CODE DEFINITIONS

Note. Use of Tech 2(R) or generic OBD-II scan tool is required to retrieve DTCs. Refer to user reference manual supplied using scan tool.

DIAGNOSTIC TROUBLE CODE DEFINITIONS

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MIL INOPERATIVE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Circuit Description

Battery positive voltage is supplied directly to the Malfunction Indicator Light (MIL). The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition switch in RUN position and the engine OFF.

MIL Operation

MIL is located on instrument panel and is displayed as CHECK ENGINE light.

MIL Function

1. The MIL informs driver that a malfunction has occurred and vehicle should be taken in for service as soon as possible.
2. The MIL illuminates during a bulb test and a system test.
3. A DTC will be stored if a MIL is requested by the diagnostic.

MIL Illumination

1. The MIL will illuminate with ignition switch to RUN position and engine not running.
2. The MIL will turn OFF when the engine is started.
3. The MIL will remain ON if the self-diagnostic system has detected a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If MIL is illuminated and then the engine stalls, MIL will remain illuminated so long as ignition switch is in RUN position.
6. If MIL is not illuminated and the engine stalls, MIL will not illuminate until ignition switch is cycled OFF, then ON.

The number below refers to the step number in the diagnostic procedures.

1. 2 - This step tests for a short to voltage on the MIL control circuit. With the fuse removed there should be no voltage on the MIL control circuit.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Verify whether the instrument cluster is operational. If the Instrument Panel (IP) is completely inoperative, see DIAGNOSTIC SYSTEM CHECK - INSTRUMENT CLUSTER in appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Command the MIL ON and OFF, using scan tool. Does the MIL turn ON and OFF when commanded using a scan tool? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to next step.
3. Check the fuse that supplies battery positive voltage to the MIL. Is the fuse open? If yes, go to step 10 . If no, go to next step.
4. Turn ignition switch to OFF position. Remove the fuse that supplies voltage to the MIL. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position, engine OFF. Measure voltage between the MIL control circuit in the PCM harness connector and a good ground. Is the voltage less than 0.3 volt? If yes, go to next step. If no, go to step 11 .
5. Turn ignition switch to OFF position. Install the fuse that supplies voltage to the MIL. Turn ignition switch to RUN position, engine OFF. Connect a 3-amp fused jumper wire between the MIL control circuit in the PCM harness connector and a good ground. Is the MIL illuminated? If yes, go to step 9 . If no, go to next step.
6. Turn ignition switch to OFF position. Remove the Instrument Panel Cluster (IPC). Go to appropriate INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT for removal and installation procedures. Probe the IPC harness connector MIL battery positive voltage circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 12 .
7. Check the MIL control circuit for an open or high resistance. Did you find and correct a condition? If yes, go to step 15 . If no, go to next step.
8. Check for an intermittent and for a poor connection at the IPC. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
9. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
10. Repair the short to ground in the battery positive voltage circuit. After repair, go to step 15 .
11. Repair the short to voltage in the MIL control circuit. After repair, go to step 15 .
12. Repair the open in the MIL battery positive voltage circuit. After repair, go to step 15 .
13. Replace the IPC. Go to appropriate INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT. After repair, go to step 15 .
14. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
15. Remove all test equipment. Connect any disconnected components or any disconnected fuses. Turn ignition switch to OFF position for 30 seconds. Does the vehicle operate correctly, without any MIL illumination and without any stored DTCs? If yes, system is okay at this time. If no, diagnose appropriate DTC. Go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) .

MIL ALWAYS ON

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Battery positive voltage is supplied directly to the Malfunction Indicator Light (MIL). The PCM turns the MIL ON by grounding the MIL control circuit.

MIL is located on the instrument panel and is displayed as CHECK ENGINE light.

MIL Function

1. The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
2. The MIL illuminates during a bulb test and a system test.
3. A DTC will be stored if a MIL is requested by the diagnostic.

MIL Illumination

1. The MIL will illuminate with ignition switch in RUN position and the engine not running.
2. The MIL will turn OFF when the engine is started.
3. The MIL will remain ON if the self-diagnostic system has detected a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is in RUN position.
6. If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

The number below refers to the step number on the diagnostic procedures.

1. 2 - This step determines if the condition is with the MIL control circuit or the PCM.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to OFF position. Disconnect PCM harness connectors. Turn ignition switch to RUN position, engine off. Observe the MIL. Is the MIL illuminated? If yes, go to next step. If no, go to step 5 .
3. Check the MIL control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
4. Replace IPC. Go to appropriate INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT. After replacing IPC, go to step 6 .
5. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
6. Turn ignition switch to OFF position for 30 seconds. Start the engine. Does the vehicle operate correctly without any unwanted MIL illumination, and without any stored DTCs? If yes, system is okay at this time. If no, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .

If the problem is intermittent, refer to go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DIAGNOSTIC TESTS

Note. Before clearing DTCs, perform powertrain diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. Record FREEZE FRAME and FAILURE RECORDS for reference during testing. Data will be erased when DTCs are cleared.

DTC P0030: HO2S 1 HEATER CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in closed loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and then provide an accurate voltage signal. The PCM controls the HO2S 1 heater low control circuit with a low side driver. The HO2S 1 heater diagnostic monitors the current draw through the HO2S 1 low side driver when the engine is running. If the PCM detects that the HO2S 1 heater low control circuit current exceeds a calibrated amount, DTC P0030 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

The engine is running.

Conditions For Setting DTC

The PCM detects that the heater control circuit current is greater than 1.25 amps for more than 20 seconds.

Actions Taken When DTC Sets

1. The Powertrain Control Module (PCM) illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions For Clearing MIL/DTC

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - Check the heater current with the engine at operating temperature, and allow time for the heater current to stabilize. The HO2S 1 heater current is initially higher until the sensor reaches full operating temperature.
2. 4 - A DTC fail in this step verifies the condition is present with the HO2S 1 disconnected.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Observe the Heated Oxygen Sensor (HO2S) 1 heater current parameter using a scan tool. Is the amperage 0.25-0.85 amp? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the HO2S 1 harness connector. Start the engine. Allow the engine to idle at operating temperature. Observe the DTC Info parameter using a scan tool for at least 30 seconds. Did the DTC fail this ignition? If yes, go to next step. If no, go to step 6 .
5. Test the HO2S 1 heater low control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 7 .
6. Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
7. Test for an intermittent and for a poor connection at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
8. Replace the HO2S 1. After repair, go to step 10 .
9. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
10. Clear the DTCs using scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
11. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits

1. An ignition 1 voltage circuit.
2. A ground circuit.
3. A signal circuit.

The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies within a range of near 2000 Hertz at idle to near 10,000 Hertz at maximum engine load. The PCM uses the following sensor inputs to calculate a predicted MAF value

1. The Barometric Pressure (BARO) at key ON.
2. The Manifold Absolute Pressure (MAP) sensor.
3. The Intake Air Temperature (IAT) sensor.
4. The Engine Coolant Temperature (ECT) sensor.
5. The Throttle Position (TP) sensor.
6. The engine speed (RPM).

The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. If the PCM detects the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value, DTC P0101 sets.

1. DTCs P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0401, P0403, P0404, P0405, P0440, P0442, P0443, P0446, P0449, P1404 or P1441 are not set.
2. The engine is running.
3. The ignition 1 signal is between 9-18 volts.
4. The TP sensor angle is less than 25 percent.
5. The change in the TP sensor angle is less than 1.5 percent.
6. The MAP sensor parameter is less than 63 kPa.
7. The change in the MAP sensor is less than 3 kPa.
8. The conditions are met for more than 5 seconds.

The PCM detects that the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value for more than 10 seconds.

Action Taken When DTC Sets

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - This step will determine if the MAP sensor pressure is within the proper range for a given altitude.
2. 6 - This step will determine if the MAP sensor voltage is within the proper range at idle.
3. 7 - This step will determine if the MAP sensor responds properly to the change in manifold pressure.
4. 8 - This step will determine if the TP sensor is operating properly.
5. 9 - This step will determine if any mechanical faults have caused this DTC to set.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Attempt to start the engine. Does the engine start? If yes, go to next step. If no, go to step 4 .
3. Observe the Diagnostic Trouble Code (DTC) Information using the scan tool. Does the scan tool display any other DTCs set? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Turn ignition switch to RUN position, engine OFF. Observe the Manifold Absolute Pressure (MAP) sensor parameter using the scan tool. The MAP sensor pressure should be within the specified range for your altitude. Is the MAP sensor pressure within the specified range as indicated on the Altitude vs Barometric Pressure table? If yes, go to next step. If no, go to «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
6. Start the engine. Turn OFF all accessories. Allow the engine to reach operating temperature. Observe the MAP sensor parameter using a scan tool. Is the MAP sensor parameter 0.8-2.0 volts? If yes, go to next step. If no, go to «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
7. Idle the engine. Observe the MAP sensor parameter using a scan tool. Increase the engine speed slowly to 3000 RPM and then back to idle. Does the MAP sensor parameter change smoothly and gradually through the specified range of the test? If yes, go to next step. If no, go to «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
8. Turn ignition switch to OFF position for 30 seconds. Turn ignition switch to RUN position, engine OFF. Observe the TP sensor parameter at closed throttle using a scan tool. Depress the accelerator pedal completely. Observe the TP sensor parameter at wide open throttle using a scan tool. Does the TP sensor parameter change from zero percent to 100 percent? If yes, go to next step. If no, go to «DTC P0121: TP SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
9. Turn ignition switch to OFF position. Check for the following conditions: A restricted or collapsed air intake duct. A misaligned air intake duct. A dirty or deteriorating air filter element. Any objects blocking the air inlet screen of the Mass Airflow (MAF) sensor. Any contamination or debris on the sensing elements of the MAF sensor. Any water intrusion in the induction system. Any vacuum leak downstream of the MAF sensor. A skewed or stuck Engine Coolant Temperature (ECT) sensor Any type of restriction in the exhaust system. Go to «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEM & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
10. Disconnect the MAF sensor harness connector. Turn ignition switch to RUN position, engine OFF. Connect a test light between the MAF sensor ignition 1 voltage circuit and a good ground. Connect a DMM to the test light probe and a good ground. Is the voltage within 0.50 volts of battery voltage? If yes, go to next step. If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the MAF sensor. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Repair the high resistance in the ignition 1 voltage circuit of the MAF sensor. After repair, go to step 14 .
13. Replace the MAF sensor. After repair, go to step 14 .
14. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

(1) ALTITUDE VS. BAROMETRIC PRESSURE

1. Check the MAF sensor harness to verify that it is not routed too close to secondary ignition wires or coils, any solenoids, relays or motors.
2. A low minimum air rate through the sensor bore at idle or during deceleration may cause this DTC to set. Check for any deposits on the throttle plate or in the throttle bore or any vacuum leak downstream of the MAF sensor.
3. Check for any contamination or debris on the sensing elements of the MAF sensor.
4. Check the air induction system for any water intrusion. Any water that reaches the MAF sensor will skew the sensor and may cause this DTC to set.
5. A wide open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 3-10 g/s at idle to 130 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
6. Check for a skewed or stuck ECT sensor.
7. Check for a skewed or stuck TP sensor.
8. The barometric pressure used to calculate the predicted mass air flow value is initially based on the MAP sensor at key ON. When the engine is running the BARO value is continually updated near wide open throttle. A skewed MAP sensor will cause the calculated MAF value to be inaccurate and may result in a no start condition. The value shown for the MAP sensor parameter varies with the altitude. With ignition switch in RUN position and the engine OFF, 101 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 1000 feet (305 meters) of altitude.
9. A high resistance on the low reference circuit of the MAP sensor may cause this DTC to set.
10. A high resistance on the signal or the low reference circuit of the ECT sensor may cause this DTC to set.
11. If the condition is intermittent, See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits

1. An ignition 1 voltage circuit.
2. A ground circuit.
3. A signal circuit.

The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies within a range of near 2000 Hertz at idle to near 10,000 Hertz at maximum engine load. If the PCM detects the frequency signal is less than the possible range of a correctly operating MAF sensor DTC P0102 sets.

1. The engine is running.
2. The ignition 1 signal is more than 8 volts.
3. The Idle Air Control (IAC) position is more than 2 counts.
4. The conditions are met for more than 0.5 second.

The PCM detects that the MAF sensor frequency signal is less than 1200 Hz.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - This step will determine if any mechanical faults have caused this DTC to set.
2. 7 - This voltage drop test will determine if high resistance has caused this DTC to set.
3. 9 - This step verifies the voltage signal from the PCM to the MAF sensor connector.
4. 10 - This step tests the signal circuit of the MAF sensor for a short to another 5-volt reference circuit.
5. 11 - This step will determine if the PCM is able to process the frequency signal that it receives from the MAF sensor.
6. 14 - This step will determine which portion of the circuit or which component is shorted to ground.
7. 17 - This step verifies that the signal circuit is not shorted to any other PCM circuit.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Observe the MAF Sensor parameter using the scan tool. Is the MAF Sensor parameter less than 1200 Hz? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Observe the Mass Airflow (MAF) sensor parameter using the scan tool. Move the harness and the connector of the MAF sensor. Does the movement of the harness or the connector affect the MAF sensor parameter? If yes, go to step 20 . If no, go to next step.
5. Turn ignition switch to OFF position. Check for the following conditions: A restricted or collapsed air intake duct. A misaligned air intake duct. A dirty or deteriorating air filter element. Any objects blocking the air inlet screen of the MAF sensor. Any contamination or debris on the sensing elements of the MAF sensor. Did you find and correct the condition? If yes, go to step 28 . If no, go to next step.
6. Check the fuse in the ignition 1 voltage circuit of the MAF sensor. See «WIRING DIAGRAMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Is the fuse open? If yes, go to step 14 . If no, go to next step.
7. Turn ignition switch to RUN position, engine OFF. Measure the battery voltage using a DMM. Disconnect the MAF sensor harness connector. Connect a test light between the MAF sensor ignition 1 voltage circuit and a good ground. Connect the DMM to the test light probe and a good ground. Is the voltage within 0.50 volt of battery voltage? If yes, go to next step. If no, go to step 21 .
8. Ensure all electrical components and accessories are turned OFF. Turn ignition switch to OFF position for 60 seconds to allow the control modules to power down. Measure the resistance from the MAF sensor ground circuit to a good ground using a DMM. Is the resistance less than 5 ohms? If yes, go to next step. If no, go to step 22 .
9. Turn ignition switch to RUN position, engine OFF. Measure the voltage between the MAF sensor signal circuit to a good ground using the DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step 13 .
10. Connect a 3-amp fused jumper wire between the MAF sensor signal circuit and a good ground. Start the engine. Observe the DTC Information using a scan tool. Do any additional DTCs set? If yes, go to step 24 . If no, go to next step.
11. Turn ignition switch to OFF position. Connect the voltage supply and the ground lead of the Variable Signal Generator (J 38522), or equivalent, to the vehicle. Connect the Red lead of the variable signal generator to the MAF sensor signal circuit. Set the Duty Cycle switch of the variable signal generator to NORMAL. Set the Frequency switch of the variable signal generator to 5K. Set the Signal switch of the variable signal generator to 5 VOLTS. Start the engine. Observe the MAF Sensor parameter using a scan tool. Is the MAF Sensor parameter 4950-5025 Hz? If yes, go to next step. If no go to step 15 .
12. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Test the MAF sensor signal circuit for a high resistance. Did you find and correct the condition? If yes, go to step 28 . If no, go to step 16 .
13. Is the voltage less than 4.8 volts? If yes, go to step 15 . If no go to step 16 .
14. Test the ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 28 .
15. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Test the signal circuit between the PCM and the MAF sensor for high resistance, an open circuit, or short to ground. Did you find and correct the condition? If yes, go to step 28 . If no, go to step 17 .
16. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the signal circuit of the MAF sensor to a good ground using the DMM. Is the voltage more than zero volts? If yes, go to step 23 . If no, go to next step.
17. Measure the resistance from the MAF sensor signal circuit to all other circuits at both PCM connectors using a DMM. Is the resistance less than infinity? If yes, go to step 25 . If no, go to step 19 .
18. Test for an intermittent and for a poor connection at the MAF sensor. Did you find and correct the condition? If yes, go to step 28 . If no, go to step 26 .
19. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 28 . If no, go to step 27 .
20. Repair the wiring or the connector as needed. After repair, to step 28 .
21. Repair the high resistance or the open in the MAF sensor ignition 1 voltage circuit. After repair, to step 28 .
22. Repair the high resistance or the open in the MAF sensor ground circuit. After repair, to step 28 .
23. Repair the short to voltage in the MAF sensor signal circuit. After repair, to step 28 .
24. Repair the short between the MAF sensor signal circuit and the 5-volt reference circuit for which the DTC set. After repair, to step 28 .
25. Repair the circuits that are shorted together. After repair, to step 28 .
26. Replace the MAF sensor. After repair, to step 28 .
27. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
28. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
29. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Check the harness of the MAF sensor to verify that it is not routed too close to the secondary ignition wires or coils, any solenoids, relays or motors.
2. Check for any contamination or debris on the sensing elements of the MAF sensor.
3. A wide-open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 3-10 g/s at idle to 130 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
4. A high resistance of 15 ohms or more on the ground circuit of the MAF sensor may cause this DTC to set. A high resistance may cause a driveability concern before this DTC sets.
5. A high resistance of 15 ohms or more on the ignition 1 voltage circuit may cause this DTC to set. A high resistance may cause a driveability concern before this DTC sets.
6. If the condition is intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits

1. An ignition 1 voltage circuit.
2. A ground circuit.
3. A signal circuit.

The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies within a range of near 2000 Hertz at idle to near 10,000 Hertz at maximum engine load. If the PCM detects the frequency signal is less than the possible range of a correctly operating MAF sensor DTC P0102 sets.

1. The engine is running.
2. The ignition 1 signal is more than 8 volts.
3. The Idle Air Control (IAC) position is more than 2 counts.
4. The conditions are met for more than 0.5 second.

The PCM detects that the MAF sensor frequency signal is less than 1200 Hz.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions For Clearing the MIL/DTC

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - This step will determine if any mechanical faults have caused this DTC to set.
2. 7 - This voltage drop test will determine if high resistance has caused this DTC to set.
3. 9 - This step verifies the voltage signal from the PCM to the MAF sensor connector.
4. 10 - This step tests the signal circuit of the MAF sensor for a short to another 5-volt reference circuit.
5. 12 - This step will determine which portion of the circuit or which component is shorted to ground.
6. 15 - This step verifies that the signal circuit is not shorted to any other PCM circuit.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Observe the MAF Sensor parameter using the scan tool. Is the MAF Sensor parameter less than 1200 Hz? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Observe the MAF Sensor parameter using the scan tool. Move the Mass Airflow (MAF) sensor connector and the harness. Does the movement of the connector or the harness affect the MAF Sensor parameter? If yes, go to step 18 . If no, go to next step.
5. Turn ignition switch to OFF position. Check for the following conditions: A restricted or collapsed air intake duct. A misaligned air intake duct. A dirty or deteriorating air filter element. Any objects blocking the MAF sensor air inlet screen. Any contamination or debris on the MAF sensor sensing elements. Did you find and correct the condition? If yes, go to step 26 . If no, go to next step.
6. Check the fuse in the MAF sensor ignition 1 voltage circuit. See «WIRING DIAGRAMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Is the fuse open? If yes, go to step 12 . If no, go to next step.
7. Turn ignition switch to RUN position, engine OFF. Disconnect the MAF sensor harness connector. Connect a test light between the MAF sensor ignition 1 voltage circuit and a good ground. Connect the DMM to the test light probe and a good ground. Is the voltage less than battery voltage? If yes, go to step 19 . If no, go to next step.
8. Ensure all electrical components and accessories are turned OFF. Turn ignition switch to OFF position for 60 seconds to allow the control modules to power down. Measure the resistance from the MAF sensor ground circuit to a good ground using a DMM. Is the resistance less than 5 ohms? If yes, go to next step. If no, go to step 20 .
9. Turn ignition switch to RUN position, engine OFF. Measure the voltage between the MAF sensor signal circuit and a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step 11 .
10. Connect a 3-amp fused jumper wire between the MAF sensor signal circuit and a good ground. Start the engine. Observe the DTC Information using a scan tool. Do any additional DTCs set? If yes, go to step 22 . If no, go to step 16 .
11. Is the voltage less than 4.5 volts? If yes, go to step 13 . If no go to step 14 .
12. Test the ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 .
13. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Test the signal circuit between the PCM and the MAF sensor for high resistance, an open circuit, or short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 15 .
14. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the signal circuit of the MAF sensor to a good ground using a DMM. Is the voltage more than zero volts? If yes, go to step 21 . If no, go to next step.
15. Measure the resistance from the MAF sensor signal circuit to all other circuits at both PCM connectors using a DMM. Is the resistance less than infinity? If yes, go to step 23 . If no, go to step 17 .
16. Test for an intermittent and for a poor connection at the MAF sensor. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
17. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 25 .
18. Repair the wiring or the connector as needed. After repair, to step 26 .
19. Repair the high resistance or the open in the MAF sensor ignition 1 voltage circuit. After repair, to step 26 .
20. Repair the high resistance or the open in the MAF sensor ground circuit. After repair, to step 26 .
21. Repair the short to voltage in the MAF sensor signal circuit. After repair, to step 26 .
22. Repair the short between the MAF sensor signal circuit and the 5-volt reference circuit for which the DTC set. After repair, to step 26 .
23. Repair the circuits that are shorted together. After repair, to step 26 .
24. Replace the MAF sensor. After repair, go to step 26 .
25. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
26. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
27. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Check the harness of the MAF sensor to verify that it is not routed too close to the secondary ignition wires or coils, any solenoids, relays or motors.
2. Check for any contamination or debris on the sensing elements of the MAF sensor.
3. A wide-open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 3-10 g/s at idle to 130 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
4. A high resistance of 15 ohms or more on the ground circuit of the MAF sensor may cause this DTC to set. A high resistance may cause a driveability concern before this DTC sets.
5. A high resistance of 15 ohms or more on the ignition 1 voltage circuit may cause this DTC to set. A high resistance may cause a driveability concern before this DTC sets.
6. If the condition is intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0103: MAF SENSOR CIRCUIT - HIGH FREQUENCY

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor frequency signal to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following

1. An ignition 1 voltage circuit.
2. A ground circuit.
3. A signal circuit.

The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2000 Hertz at idle to about 10,000 Hertz at maximum engine load. DTC P0103 sets if the PCM detects a frequency signal higher than the possible range of a properly operating sensor.

1. The engine is running.
2. The ignition 1 signal is more than 8 volts.
3. The Idle Air Control (IAC) position is more than 2 counts.
4. The above conditions are met for more than 0.5 second.

The PCM detects that the MAF sensor frequency signal is more than 11,500 Hz.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 3 - This step tests for Electromagnetic Interference (EMI) on the signal circuit of the MAF sensor. A frequency reading with the MAF sensor disconnected may indicate an EMI related fault or a poor connection at the PCM. Disconnecting the MAF sensor may set additional related DTCs.
2. 4 - This step will determine if incorrect harness routing has caused this DTC to set.
3. 5 - This step will determine if water intrusion has caused this DTC to set.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Turn ignition switch to OFF position. Disconnect the MAF sensor harness connector. Start the engine. Observe the MAF sensor parameter using a scan tool. Is the MAF sensor parameter more than zero Hz? If yes, go to next step. If no, go to step 5 .
4. Turn ignition switch to OFF position. Check the MAF sensor harness for incorrect routing that is too close to the following components: The secondary ignition wires or the coils. Any solenoids. Any relays. Any motors. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 7 .
5. Turn ignition switch to OFF position. Check the air induction system for any water intrusion. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
6. Test for an intermittent and for a poor connection at the MAF sensor. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
7. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 9 .
8. Replace the MAF sensor. After repair, go to step 10 .
9. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
10. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
11. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Check the air induction system for any water intrusion. The water rapidly cools the hot sensing elements in the sensor causing a false indication of excessive air flow. Any water that reaches the MAF sensor will skew the sensor and may cause this DTC to set.
2. A poor connection in the ignition 1 voltage circuit of the MAF sensor may cause this DTC to set.
3. If the condition is intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0107: MANIFOLD ABSOLUTE PRESSURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition in RUN position, engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned to RUN position, engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

1. DTCs P0121, P0122 or P0123 are not set.
2. The engine is running.
3. The throttle angle is more than zero percent, if the engine speed is less than 1000 RPM.

The PCM detects that MAP sensor voltage is less than 0.1 volt for more than 3 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 4 - Operate the vehicle within the same conditions which caused the DTC to fail. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records can aid in locating an intermittent condition.
2. 5 - This step determines if voltage is available to the sensor. It also determines if there is sufficient current flow in the circuit.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Monitor the Diagnostic Trouble Code (DTC) information with the scan tool. Is DTC P1635 also set? If yes, go to «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) or «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) . If no, go to next step.
3. Observe the MAP sensor parameter using a scan tool. Is the voltage less than 0.1 volt? If yes, go to step 5 . If no, go to next step.
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Turn ignition switch to OFF position. Disconnect the MAP sensor harness connector. Turn ignition switch to RUN position, engine OFF. Probe the MAP sensor 5-volt reference circuit using a test light connected to a good ground. Is the test light OFF? If yes, go to step 7 . If no, go to next step.
6. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the MAP sensor and the signal circuit of the MAP sensor. Observe the MAP sensor parameter using the scan tool. Is the voltage more than 4.9 volts? If yes, go to step 9 . If no, go to step 8 .
7. Test the 5-volt reference circuit between the PCM and MAP sensor for an open or high resistance. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
8. Check for faulty connections at the MAP sensor. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 11 .
10. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
11. Replace the MAP sensor. After repair, go to step 13 .
12. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
13. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
14. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

If a components 5-volt reference circuit is shorted to ground or shorted to voltage, the other 5-volt reference circuits may be affected.

If this DTC is determined to be intermittent, refer to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0108: MANIFOLD ABSOLUTE PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition switch in RUN position, engine OFF, or at Wide Open Throttle (WOT). The MAP sensor is also used to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned to RUN position, engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set.

1. DTCs P0121, P0122 or P0123 are not set.
2. The engine has been running for a length of time that is determined by the start-up coolant temperature. The length of time ranges from 2 minutes at less than -22°F (-30°C) to one second at more than 86°F (30°C).
3. The throttle angle is less than 2 percent when the engine speed is less than 3000 RPM or the throttle angle is less than 30 percent when the engine speed is more than 3000 RPM.

The PCM detects that the MAP sensor voltage is more than 4.3 volts for at least 3 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 3 - This step tests for improper Throttle Position (TP) sensor operation.
2. 5 - If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. With the engine OFF, monitor the Diagnostic Trouble Code (DTC) information using the scan tool. Is DTC P1635 also set? If yes, go to «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) or «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) . If no, go to next step.
3. Observe the TP sensor parameter using the scan tool. Depress the accelerator pedal slowly until the throttle is in the wide open position. Release the accelerator pedal slowly until the throttle is returned to the closed position. Repeat this procedure several times. Does the TP sensor parameter increase steadily to more than 98 percent, and then decrease steadily returning to less than one percent? If yes, go to next step. If no, go to «DTC P0121: TP SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Start the engine. Observe the MAP sensor parameter using a scan tool. Is the voltage more than 4.3 volts? If yes, go to step 6 . If no, go to next step.
5. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to step 6 . If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
6. Turn ignition switch to OFF position. Check the MAP sensor and the vacuum source for the following conditions: Vacuum line disconnected from the MAP sensor. Vacuum line pinched or cut. Blocked port. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
7. Disconnect the MAP sensor harness connector. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor parameter using the scan tool. Is the voltage less than 0.1 volt? If yes, go to next step. If no, go to step 9 .
8. Turn ignition switch to OFF position. Disconnect the Engine Coolant Temperature (ECT) sensor harness connector. Connect a jumper wire between each of the terminals in the MAP sensor harness connector and the corresponding terminal at the MAP sensor. Turn ignition switch to RUN position, engine OFF. Measure voltage from the MAP sensor low reference circuit at the jumper wire terminal to a good ground using a DMM. Is the voltage more than 0.2 volt? If yes, go to step 10 . If no, go to step 11 .
9. Test the MAP sensor signal circuit between the PCM and the MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
10. Test the low reference circuit between the PCM and the MAP sensor for high resistance or for an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
11. Test for an intermittent and for a poor connections at the MAP sensor. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Test for an intermittent and for a poor connections at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
13. Replace MAP sensor. After repair, go to step 15 .
14. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
15. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
16. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0112: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0125, P0128, P0502 or P0503 are not set.
2. The engine run time is more than 10 seconds.
3. The Vehicle Speed Sensor (VSS) indicates that vehicle speed is more than 25 MPH.

The PCM detects that the IAT sensor parameter is more than 253°F (123°C) for 6 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Intake Air Temperature (IAT) sensor parameter using a scan tool. Is the IAT sensor parameter more than 262°F (128°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC reset? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect IAT sensor harness connector. Turn ignition switch to RUN position, engine off. Observe the IAT sensor temperature using a scan tool. Is the IAT sensor temperature less than -36°F (-38°C). If yes, go to step 6 . If no, go to next step.
5. Check the signal circuit of the IAT sensor for a short to ground or a short to IAT low reference circuit. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
6. Check for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
7. Replace the IAT sensor. After repair, go to step 10 .
8. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
9. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
10. Use the scan tool to clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
11. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0113: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively high IAT signal voltage, indicating a low temperature, DTC P0113 sets.

1. DTCs P0116, P0117, P0118, P0125, P0128, P0502 or P0503 are not set.
2. The engine run time is more than 180 seconds.
3. The Vehicle Speed Sensor (VSS) indicates that vehicle speed is less than 35 MPH.
4. The Mass Airflow (MAF) sensor parameter is less than 12 g/s.
5. The Engine Coolant Temperature (ECT) sensor parameter is more than 140°F (60°C).

The IAT sensor signal voltage indicates that the intake air temperature is less than -36°F (-38°C) for 3 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 6 - This step tests for the proper operation of the circuit in the low voltage range.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine off. Observe the IAT sensor parameter. Is the IAT sensor temperature less than -36°F (-38°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC reset? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect IAT sensor harness connector. Connect a DMM between the IAT sensor signal circuit and a good ground. Turn ignition switch to RUN position. Does the DMM voltage measure more than 5.2 volts? If yes, go to next step. If no, go to step 6 .
5. Check the signal circuit for a short to voltage. Repair as necessary. Did you find and correct the condition? If yes, go to step 15 . If no, go to 12 .
6. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the IAT sensor signal circuit and the low reference circuit at the IAT sensor harness connector. Turn ignition switch to RUN position, engine off. Observe the IAT sensor temperature using a scan tool. Is the IAT sensor temperature more than 262°F (128°C)? If yes, go to step 10 . If no, go to next step.
7. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the signal circuit of the IAT sensor harness connector and a known-good ground. Turn ignition switch to RUN position, engine off. Observe the IAT sensor temperature using a scan tool. Is the IAT sensor temperature more than 262°F (128°C)? If yes, go to step 9 . If no, go to next step.
8. Check the IAT sensor signal circuit for an open circuit or high resistance. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
9. Check the IAT sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
10. Check the IAT signal circuit for a short to any 5-volt reference circuit. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
11. Check for an intermittent and for a poor connection at the IAT sensor. Repair as necessary. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Check for an intermittent and for a poor connection at the PCM. Repair as necessary. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
13. Replace the IAT sensor. After repair, go to step 15 .
14. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
15. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to 2 .
16. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0116: ECT SENSOR CIRCUIT PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the signal circuit and a ground for the ECT low reference circuit. When the engine coolant temperature is low, the sensor resistance is high. When the engine coolant temperature is high, the sensor resistance is low. The PCM uses this High Side Coolant Rationality test to determine if the ECT input is skewed high. The internal clock of the PCM will record the amount of time the ignition is OFF. At restart the PCM will compare the temperature difference between the ECT and the Intake Air Temperature (IAT). Before failing this test, the PCM will perform a calculation to determine the presence of an engine block heater. If the PCM detects that the temperature difference between the ECT and the IAT is not within the calibrated range after the ignition OFF time, DTC P0116 sets.

1. The ignition switch is in RUN position.
2. DTCs P0112, P0113, P0117, P0118, P0125, P0128, P0601, P0602, P1621 or P1683 are not set.
3. The vehicle has a minimum ignition OFF time of 8 hours.

1. The PCM detects a temperature difference between the ECT sensor and the IAT sensor of more than 180°F (82°C) at start up.
2. The time spent cranking the engine, without starting is more than 5 seconds with a temperature difference between the ECT sensor and the IAT sensor more than 27°F (15°C).
3. The PCM detects a temperature difference between the ECT sensor and the IAT sensor of more than 27°F (15°C), then the vehicle must be driven for 5 minutes over 15 MPH. If the IAT sensor temperature decreases more than 12.6°F (7°C), then a block heater is detected and the test is aborted. If the IAT sensor temperature does not decrease, than a block heater was not detected and DTC P0116 sets.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 7 - An IAT sensor that is skewed low can cause this DTC to set.
2. 8 - A snapshot is the quickest method to capture the data before it changes.
3. 10 - This step will determine if high resistance has caused this DTC to set.
4. 12 - A high resistance short from the signal circuit to the low reference circuit can cause this DTC to set.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Check the cooling system coolant level. Is the cooling system coolant low? If yes, repair cause of coolant loss and refill system.
3. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. After completing the action, go to next step.
4. Has the engine been OFF for 8 hours? If yes, go to step 7 . If no, go to next step.
5. Remove the IAT sensor. Remove the ECT sensor. Place the sensors on a work surface away from any heat source. Allow the sensors to reach the ambient air temperature for 30-60 minutes. After the sensors at the ambient temperature, go to next step.
6. Connect the IAT sensor to the IAT harness connector, but Do NOT install it. Insulate the sensor from any engine heat source. Connect the ECT sensor to the ECT harness connector, but Do NOT install it. Insulate the sensor from any engine heat source. After the sensors connected, go to next step.
7. Turn ignition switch to RUN position. Take a snapshot of the ENGINE DATA LIST using a scan tool. Review the snapshot data that was taken. Observe the ECT Sensor parameter. Observe the IAT Sensor parameter. Is the difference between the ECT Sensor parameter and the IAT Sensor parameter more than 27°F (15°C)? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
8. Observe the recorded IAT Sensor parameter. Is the difference between the IAT Sensor parameter and the ambient air temperature less than 14°F (8°C)? If yes, go to next step. If no, go to step 12 .
9. Observe the recorded ECT Sensor parameter. Is the difference between the ECT Sensor parameter and the ambient air temperature less than 14°F (8°C)? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 12 .
10. Disconnect the IAT sensor harness connector. Test for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
11. At the sensor, measure the resistance between the IAT signal and the IAT low reference terminals using a DMM and record the value. Observe the recorded ambient air temperature. Compare the resistance measurement of the IAT sensor to the ambient air temperature using the Temperature vs. Resistance table. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) table. Is the resistance measurement of the IAT sensor within the specified range? If yes, go to step 14 . If no, go to step 22 .
12. Disconnect the ECT sensor harness connector. Check for the following conditions: An ECT sensor leaking engine coolant internally through the sensor. Corrosion on the ECT sensor terminals. Corrosion on the ECT harness connector terminals. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
13. At the sensor, measure the resistance between the ECT signal and the ECT low reference terminals using a DMM and record the value. Observe the recorded ambient air temperature. Compare the resistance measurement of the ECT sensor to the ambient air temperature using the Temperature vs. Resistance table. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) table. Is the resistance measurement of the ECT sensor within the specified range? If yes, go to step 15 . If no, go to step 23 .
14. Measure the voltage from the IAT signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 17 .
15. Measure the voltage from the ECT signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 19 .
16. Turn ignition switch to OFF position for 90 seconds to allow the control modules to power down. Measure the resistance from the IAT sensor low reference circuit to a good ground using a DMM. Is the resistance less than 5 ohms? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 18 .
17. Test the IAT signal circuit for a high resistance. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 20 .
18. Test the ECT signal circuit for a high resistance short to ground. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 20 .
19. Test the ECT signal circuit for a high resistance short to ground. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 21 .
20. Test for an intermittent and for a poor connection at the Powertrain Control Module (PCM). Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
21. Test for shorted terminals and poor connections at the PCM. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
22. Replace the IAT sensor. After repair, go to step 25 .
23. Replace the IAT sensor. After repair, go to step 25 .
24. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
25. Reassemble the vehicle as necessary. After repair, go to next step.
26. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 8 hours. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
27. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

TEMPERATURE VS. RESISTANCE

DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

The engine is running.

The PCM detects that the ECT sensor parameter is more than 280°F (138°C) for more than 15 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Connect scan tool. Turn ignition switch to RUN position, engine off. Observe the ECT sensor parameter. Does the scan tool indicate that the ECT sensor temperature is more than 280°F (138°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Disconnect ECT sensor harness connector. Turn ignition switch to RUN position, engine off. Using a scan tool, observe the ECT sensor temperature. Does the scan tool indicate that the ECT sensor temperature is less than -36°F (-38°C). If yes, go to step 6 . If no, go to next step.
5. Check the ECT sensor signal circuit for a short to ground or a short to any low reference circuit. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
6. Check for an intermittent and for a poor connection at the ECT sensor. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
7. Replace ECT sensor. After repair, go to step 10 .
8. Check for an intermittent and for a poor connection at the Powertrain Control Module (PCM). Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
9. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
10. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
11. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.

The engine is running.

The PCM detects that the ECT sensor parameter less than -38°F (-39°C) for more than 15 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Connect scan tool. Turn ignition switch to RUN position, engine off. Using a scan tool, observe the ECT sensor parameter. Does the scan tool indicate that the ECT sensor temperature is less than -36°F (-38°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect ECT sensor harness connector. Measure the voltage from the ECT sensor signal circuit to a good ground using a DMM. Is the voltage more than 5.2 volts? If yes, go to next step. If no, go to step 6 .
5. Check the ECT signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
6. Connect a 3-amp fused jumper between the ECT sensor signal circuit and the low reference circuit. Observe the ECT sensor parameter using the scan tool. Is the ECT sensor parameter more than 280°F (138°C)? If yes, go to step 10 . If no, go to next step.
7. Connect a 3-amp fused jumper wire between the ECT sensor signal circuit and a good ground. Observe the ECT sensor parameter using a scan tool. Is the ECT sensor parameter more than 280°F (138°C)? If yes, go to step 9 . If no, go to next step.
8. Check the ECT sensor signal circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
9. Check the ECT sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
10. Check the ECT signal circuit for a short to any 5-volt reference circuit. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
11. Check for an intermittent and for a poor connection at the ECT sensor. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
13. Replace the ECT sensor. After repair, go to step 15 .
14. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
15. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate he vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
16. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that have not been diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with three circuits

1. A 5-volt reference circuit.
2. A low reference circuit
3. A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. When the conditions for running this DTC are met the PCM will use the Manifold Absolute Pressure (MAP) sensor to determine if the predicted operating range of the TP sensor is correct. If the PCM detects the TP sensor voltage is out of the predicted range, DTC P0121 sets.

1. DTC P0107, P0108, P0122 or P0123 are not set.
2. The engine has been running for more than 2 minutes.
3. The Engine Coolant Temperature (ECT) sensor parameter is more than 167°F (75°C).
4. The MAP reading is less than 50 kPa for a TP sensor skewed high test.
5. The MAP reading is more than 70 kPa for a TP sensor skewed low test.
6. The MAP is steady for 5 seconds or more.

1. The TP sensor reading is more than a predicted value when the MAP is less than 50 kPa.
2. The TP sensor reading is less than a predicted value when the MAP is above 70 kPa.
3. The above conditions are present for 5 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns off the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Check for the following conditions: Any vacuum hoses disconnected, damaged, or incorrectly routed. The Manifold Absolute Pressure (MAP) sensor vacuum hose disconnected or damaged. Restrictions in the MAP sensor vacuum source. Any intake manifold vacuum leaks. Did you find and correct the condition? If yes, go to step 24 . If no, go to next step.
3. Do you have access to another vehicle in which the MAP sensor pressure can be observed using a scan tool? If yes, go to next step. If no, go to step 5 .
4. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor pressure using a scan tool. Observe the MAP sensor pressure in the known good vehicle using a scan tool. Compare the values. Is the difference between the values less than 3 kPa? If yes, go to step 6 . If no, go to «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor pressure using a scan tool. See «ALTITUDE VS. BAROMETRIC PRESSURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) table. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP sensor indicate the correct barometric pressure? If yes, go to next step. If no, go to «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
6. Observe the MAP sensor pressure using a scan tool. Start the engine. Does the MAP sensor pressure change? If yes, go to next step. If no, go to «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
7. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Observe the Throttle Position (TP) sensor parameter using the scan tool. Is the voltage less than 0.90 volt with the throttle in the closed position? If yes, go to next step. If no, go to step 9 .
8. Observe the TP sensor parameter using the scan tool. Depress the accelerator pedal slowly until the throttle is in the wide open position. Release the accelerator pedal slowly until the throttle is returned to the closed position. Repeat this procedure several times. Does the TP sensor parameter increase steadily to more than 98 percent, and then decrease steadily returning to less than one percent? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 10 .
9. Check the throttle body for the following conditions: A binding or damaged throttle blade. Binding or damaged throttle cable. Did you find and correct the condition? If yes, go to step 24 . If no, go to next step.
10. Disconnect the TP sensor harness connector. Observe the TP sensor parameter using the scan tool. Is the voltage less than 0.1 volt? If yes, go to next step. If no, go to step 15 .
11. Measure the voltage from the TP sensor 5-volt reference circuit to a good ground using a DMM. Is the voltage more than 5.2 volts? If yes, go to step 16 . If no, go to next step.
12. Probe the TP sensor 5-volt reference circuit using a test light connected to a good ground. Is the test light OFF? If yes, go to step 17 . If no, go to next step.
13. Connect a 3-amp fused jumper wire between the TP sensor 5-volt reference circuit and the TP sensor signal circuit. Observe the TP sensor parameter using the scan tool. Is the voltage more than 4.9 volts? If yes, go to next step. If no, go to step 18 .
14. Turn ignition switch to OFF position. Remove the jumper wire. Connect a jumper wire between each of the terminals in the TP sensor harness connector and the corresponding terminal at the TP sensor. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the TP sensor low reference circuit at the jumper wire terminal to a good ground using a DMM. Is the voltage more than 0.2 volt? If yes, go to step 19 . If no, go to step 20 .
15. Test the TP sensor signal circuit between the PCM and the TP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 23 .
16. Test all of the branches of the 5-volt reference circuit that are shared with the TP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 23 .
17. Test the 5-volt reference circuit between the PCM and the TP sensor for an open or for a high resistance. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 21 .
18. Test the TP sensor signal circuit between the PCM and the TP sensor for the following conditions: A short to ground. An open. A high resistance. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 21 .
19. Test the low reference circuit between the PCM and the TP sensor for an open or for a high resistance. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 21 .
20. Test for an intermittent and for a poor connection at the TP sensor. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 22 .
21. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 23 .
22. Replace the TP sensor. After repair, go to step 24 .
23. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
24. Clear the DTCs using a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
25. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0122: THROTTLE POSITION SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. If the PCM detects an very low signal voltage, DTC P0122 will set.

The ignition switch is in RUN position.

The PCM detects that the TP sensor voltage is less than 0.1 volt for more than one second.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 5 - This step determines if the 5 volts supplied by the PCM is available to the sensor. It also determines if the circuit is capable of carrying the necessary amperage.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Monitor the DTC information using the scan tool. Is DTC P1635 also set? If yes, go to «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) or «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) . If no, go to next step.
3. Turn ignition switch to RUN position, engine off. Using a scan tool, observe the TP sensor voltage parameter. Does the scan tool indicate that the TP sensor voltage is less than 0.1 volt? If yes, go to step 5 . If no, go to next step.
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test or within the conditions in the Freeze Frame/Failure Records. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, go to «DTC P1122: TP SENSOR CIRCUIT INTERMITTENT - LOW VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1122-tp-sensor-circuit-intermittent) .
5. Turn ignition switch to OFF position. Disconnect the TP sensor harness connector. Turn ignition switch to RUN position, engine OFF. Probe the TP sensor 5-volt reference circuit using a test light connected to a good ground. Is the test light OFF? If yes, go to step 7 . If no, go to next step.
6. Connect a 3-amp fused jumper wire between the TP sensor 5-volt reference circuit and the TP sensor signal circuit. Observe the TP sensor parameter using a scan tool. Is the voltage more than 4.9 volts? If yes, go to step 9 . If no, go to step 8 .
7. Test the 5-volt reference circuit between the Powertrain Control Module (PCM) and the TP sensor for an open or for a high resistance. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
8. Test the TP sensor signal circuit between the PCM and the TP sensor for the following conditions: A short to ground. An open. A high resistance. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the TP sensor. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 11 .
10. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
11. Replace TP sensor. After repair, go to step 13 .
12. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
13. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
14. Using a scan tool, observe stored information. Does the scan tool display any DTCs that have not been diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0123: THROTTLE POSITION SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A TP sensor signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to greater than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively high signal voltage, this DTC will set.

The ignition switch is in RUN position.

The PCM detects that the TP sensor voltage is more than 4.9 volts for more than 1 second.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 6 - This step allows the sensor to operate and permits access to the low reference circuit for the voltage drop measurement.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Monitor the DTC information using the scan tool. Is DTC P1635 also set? If yes, go to «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) or «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) . If no, go to next step.
3. Observe the Throttle Position (TP) sensor parameter using the scan tool. Is the voltage more than 4.9 volts? If yes, go to step 5 . If no, go to next step.
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test or within the conditions in the Freeze Frame/Failure Records. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, go to «DTC P1122: TP SENSOR CIRCUIT INTERMITTENT - LOW VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1122-tp-sensor-circuit-intermittent) .
5. Turn ignition switch to OFF position. Disconnect TP sensor harness connector. Turn ignition switch to RUN position, engine off. Using a scan tool, observe the TP sensor voltage parameter. Does the scan tool indicate that the TP voltage is less than 0.1 volt? If yes, go to next step. If no, go to step 7 .
6. Turn ignition switch to OFF position. Connect a jumper wire between each of the terminals in the TP sensor harness connector and the corresponding terminal at the TP sensor. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the TP sensor low reference circuit at the jumper wire terminal to a good ground using a DMM. Is the voltage more than 0.2 volt? If yes, go to step 8 . If no, go to step 9 .
7. Test the TP sensor signal circuit between the PCM and the TP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
8. Check the low reference circuit between the PCM and the TP sensor for an open or for high resistance. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the TP sensor. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 11 .
10. Check for faulty connections at the TP sensor harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Replace TP sensor. After repair, go to step 13 .
12. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
13. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
14. Using scan tool, observe stored information. Does scan tool display any DTCs that have not been diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0125: ENGINE COOLANT TEMPERATURE INSUFFICIENT FOR CLOSED LOOP FUEL CONTROL

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Engine Coolant Temperature (ECT) sensor monitors temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the Closed Loop temperature. If the coolant temperature does not increase normally or does not reach the Closed Loop temperature, the diagnostics that use engine coolant temperature as enabling criteria may not run when expected. This DTC will only run once per ignition cycle within enabling conditions.

If the PCM detects the calibrated amount of air flow and engine run time has been met and the engine coolant has not met the Closed Loop temperature, DTC P0125 sets.

1. DTCs P0112, P0113, P0116, P0117 or P0118 are not set.
2. The engine run time is between 120-440 seconds.
3. The minimum IAT sensor parameter is more than 19°F (-7°C).
4. The start-up ECT is between -40 to 50°F (-40 to 10°C).
5. The accumulated Mass Airflow (MAF) is between 1252-5670 grams.

1. The calibrated amount of airflow has been met.
2. The calibrated amount of engine run time has been met.
3. The minimum ECT for Closed Loop of 59°F (15°C) has not been met.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is the cooling system coolant low? If yes, repair cause of coolant loss and refill system. If no, go to next step.
3. Check and verify the proper operation of the thermostat. For thermostat specifications, see appropriate SPECIFICATIONS & DRIVE BELT ROUTING article under COOLING SYSTEM (MECHANICAL). Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
4. Disconnect the ECT sensor harness connector. Check for corrosion on the ECT sensor terminals, improper or corroded terminals at the ECT harness connector and loose terminals in the ECT harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
5. Measure the voltage from the ECT sensor signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step 8 .
6. Measure the voltage from the ECT sensor signal circuit to the ECT sensor low reference circuit using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step 9 . If no, go to next step.
7. Check the ECT sensor low reference circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
8. Test the ECT sensor signal circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
9. Turn ignition switch to OFF position. Remove the ECT sensor. Place the sensor on a work surface away from any heat source. Allow the sensor to reach the ambient air temperature for 30-60 minutes. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. Measure the resistance of the ECT sensor and record the value. Compare the resistance measurement of the ECT sensor to the ambient air temperature. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) table. Is the resistance measurement of the ECT sensor within the specified range? If yes, go to step 10 . If no, go to step 12 .
10. Install the ECT sensor. After installation of ECT sensor is complete, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
11. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Reinstall ECT sensor. After installation, go to step 14 .
13. Replace ECT sensor. After repair, go to next step.
14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that have not been diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0128: ENGINE COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by PCM for engine control, and as an enabling criteria for some diagnostics.

Air flow coming into engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally, or does not reach regulating temperature of thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

This DTC will only run once per ignition cycle within the enabling condition. If the PCM detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.

1. The engine is running.
2. DTCs P0112, P0113, P0116, P0117 or P0118 are not set.
3. The ECT sensor parameter is more than -40°F (-40°C).
4. The ECT sensor parameter is less than 172°F (78°C).
5. The Intake Air Temperature (IAT) is more than 19°F (-7°C).
6. The engine has been running for more than 2 minutes, but less than 30 minutes.
7. The vehicle speed is more than 15 MPH for more than one mile.
8. The Mass Airflow (MAF) average reading is more than 15 g/s.

The PCM detects the following

1. The calibrated amount of engine run time has been met.
2. The calibrated amount of engine air flow has been met.
3. The calibrated vehicle speed and distance have been met.
4. The calibrated ECT of 176°F (80°C) has not been met.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is the cooling system coolant low? If yes, repair cause of coolant loss and refill system. If no, go to next step.
3. Check and verify the proper operation of the thermostat. For thermostat specifications, see appropriate SPECIFICATIONS & DRIVE BELT ROUTING article under COOLING SYSTEM (MECHANICAL). Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
4. Disconnect the ECT sensor harness connector. Check for corrosion on the ECT sensor terminals, improper or corroded terminals at the ECT harness connector and loose terminals in the ECT harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
5. Measure the voltage from the ECT sensor signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step 8 .
6. Measure the voltage from the ECT sensor signal circuit to the ECT sensor low reference circuit using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step 9 . If no, go to next step.
7. Check the ECT sensor low reference circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
8. Check the ECT sensor signal circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to 11 .
9. Turn ignition switch to OFF position. Remove the ECT sensor. Place the sensor on a work surface away from any heat source. Allow the sensor to reach the ambient air temperature for 30-60 minutes. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. Measure the resistance of the ECT sensor and record the value. Compare the resistance measurement of the ECT sensor to the ambient air temperature. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) table. Is the resistance measurement of the ECT sensor within the specified range? If yes, go to next step. If no, go to step 12 .
10. Install the ECT sensor. After installation, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
11. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace ECT sensor. After repair, go to step 14 .
13. Replace the PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Clear the DTCs using the scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that have not been diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

P0130: HO2S 1 CIRCUIT CLOSED LOOP PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If the PCM detects the loop status is open too long, DTC P0130 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0410, P0440, P0442, P0443, P0446, P0449, P1133, P1134 or P1441 are not set.
2. The Engine Run Time parameter is at least 4 minutes.
3. The MAF sensor parameter is between 8-35 g/s.
4. The engine speed is 550-3000 RPM.
5. The TP sensor parameter is 3-35 percent.
6. The ECT sensor parameter is more than 158°F (70°C).
7. The system voltage is 9-18 volts.

The PCM detects an active HO2S 1 with an improper voltage signal amplitude.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 6 - This step inspects the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
3. 8 - This step inspects for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control is controlled by the PCM. The engine must be running to enable the HO2S heater.
4. 9 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Wait 15 seconds to allow the HO2S 1 heater current to stabilize. Does the HO2S 1 voltage fluctuate rapidly above and below 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the HO2S 1 harness connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the HO2S 1 harness connector high signal circuit, on the engine harness side, to a good ground using a DMM. Is the HO2S 1 voltage 0.425-0.500 volt? If yes, go to next step. If no, go to step 6 .
5. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit of the engine harness and the HO2S 1 low reference circuit of the engine harness. Turn ignition switch to RUN position, engine OFF. Observe the HO2S 1 voltage using a scan tool. Is the HO2S 1 voltage less than 25 mV? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Disconnect both PCM connectors. Measure the resistance of each of the following circuits using a DMM: HO2S 1 high signal circuit between HO2S connector and the PCM connector. HO2S 1 low reference circuit between HO2S connector and the PCM connector. HO2S 1 low reference loop between PCM harness connector C1 terminal No. 29 and PCM harness connector C2 terminal No. 80. Is the resistance of each circuit less than 5 ohms? If yes, go to step 11 . If no, go to next step.
7. Repair the circuit that measured a high resistance or an open. After repair, go to step 14 .
8. Remove the jumpers from the HO2S 1 terminals. Connect a test light between the HO2S 1 ignition voltage circuit and the HO2S 1 heater low control circuit terminals, on the engine harness side. Start the engine. Does the test light illuminate? If yes, go to next step. If no, go to step «DTC P0135: HO2S 1 HEATER PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0135-ho2s-1-heater-performance) .
9. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
10. Test for an intermittent and for a poor connection at the HO2S 1 harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the PCM harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace the HO2S 1 sensor. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that have not been diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0131: HO2S 1 CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTC P0131 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The Air Fuel Ratio parameter is 12:1-16.5:1.
3. The ignition 1 signal parameter is more than 10 volts.
4. The TP sensor parameter is 3-35 percent.
5. The system voltage is 9-18 volts.

The PCM detects that the HO2S 1 voltage is less than 140 mV for more than 30 seconds or the PCM detects that the HO2S 1 voltage is less than 600 mV during Power Enrichment (PE) mode for more than 10 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 4 - A voltage reading other than bias voltage in this step indicates a short circuit condition in the high signal circuit.
3. 6 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Is the HO2S 1 voltage less than 175 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the HO2S 1 sensor harness connector. Turn ignition switch to RUN position, engine OFF. Observe the HO2S 1 voltage parameter using a scan tool. Is the HO2S 1 voltage less than 175 mV? If yes, go to next step. If no, go to step 6 .
5. Test the HO2S 1 high signal circuit for a short to ground, or a short to the HO2S 1 low reference circuit. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Check for poor connections at the harness connector. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Check for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace the HO2S 1. After repair, go to step 11 .
10. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
11. Using a scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
12. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0132: HO2S 1 CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays above the specified value, DTC P0132 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The TP sensor parameter is 3-40 percent.
3. The system voltage is 9-18 volts.

The PCM detects that the HO2S 1 voltage is more than 890 mV for more than 30 seconds or the PCM detects that the HO2S 1 voltage is more than 200 mV during Decel Fuel Cut-Off (DFCO) for more than 15 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 4 - A voltage reading other than bias voltage in this step indicates a short circuit condition in the high signal circuit.
3. 6 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Is the HO2S 1 voltage more than 975 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the scan tool indicate that this DTC failed this ignition? If yes, go to next step. If no, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect HO2S 1 sensor harness connector. Turn ignition switch to RUN position, engine off. Observe the HO2S 1 voltage parameter using a scan tool. Is the HO2S 1 voltage more than 975 mV? If yes, go to next step. If no, go to step 6 .
5. Check the HO2S 1 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Check for poor connections at the HO2S 1 sensor harness connector. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Check for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace HO2S 1. When complete, go to step 11 .
10. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
11. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
12. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0133: HO2S 1 - SLOW RESPONSE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If the PCM detects that the HO2S 1 voltage average response time is too slow, DTC P0133 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition 1 voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0410, P0440, P0442, P0443, P0446, P0449, P1133, P1134 or P1441 are not set.
2. The vehicle is not in Park or Neutral.
3. The Engine Run Time parameter is at least 60 seconds.
4. The Loop Status parameter is closed.
5. The MAF sensor parameter is between 13-30 g/s.
6. The Engine Speed parameter is 1300-3000 RPM.
7. The ECT sensor parameter is more than 158°F (70°C).
8. The system voltage is between 9-18 volts.

The PCM detects that the HO2S 1 rich-to-lean transition time takes longer than 105 milliseconds or the PCM detects that the HO2S 1 lean-to-rich transition time takes longer than 95 milliseconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 4 - A voltage reading other than the specified amount in this step indicates an open circuit condition in the high signal circuit or the PCM.
3. 6 - This step inspects the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
4. 8 - This step inspects for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control circuit driver is controlled by the PCM. The engine must be running to enable the HO2S heater.
5. 9 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Does the HO2S 1 voltage fluctuate rapidly above and below 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the scan tool indicate that this DTC failed this ignition? If yes, go to next step. If no, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect HO2S 1 harness connector. Turn ignition switch to RUN position, engine off. Using a Digital Multimeter (DMM), measure the voltage of the HO2S 1 high signal circuit on the PCM side to a good ground. Does the voltage measure 0.425-0.500 volts? If yes, go to next step. If no, go to step 6 .
5. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the HO2S 1 harness connector high signal circuit and low signal circuit. Turn ignition switch to RUN position, engine off. Use scan tool to monitor HO2S 1 voltage for the sensor that applies to this DTC. Does the scan tool indicate that the HO2S 1 voltage is less than 25 mV? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Disconnect both PCM harness connectors. Measure the resistance of each of the following circuits using a DMM: HO2S 1 high signal circuit between HO2S connector and the PCM connector. HO2S 1 low reference circuit between HO2S connector and the PCM connector. HO2S 1 low reference loop between PCM harness connector C1 terminal No. 29 and PCM harness connector C2 terminal No. 80. Is the resistance of each circuit less than 5 ohms? If yes, go to step 11 . If no, go to next step.
7. Repair the circuit that measured a high resistance or an open. After repair, go to step 14 .
8. Remove the jumpers from the HO2S 1 terminals. Connect a test light between the HO2S heater ignition voltage circuit and the heater low control circuit terminals on the engine harness side. Start the engine. Does the test light illuminate? If yes, go to next step. If no, go to «DTC P0135: HO2S 1 HEATER PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0135-ho2s-1-heater-performance) .
9. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
10. Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the PCM harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace HO2S 1. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0134: HO2S 1 CIRCUIT - INSUFFICIENT ACTIVITY

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If the PCM detects that the HO2S 1 voltage remains at or near the bias voltage amount, DTC P0134 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The Engine Run Time parameter is at least 4 minutes.
3. The system voltage is 9-18 volts.

The PCM detects that the HO2S 1 signal voltage remains between 382-525 mV for more than 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 4 - A voltage reading other than the specified amount in this step indicates an open circuit condition in the high signal circuit or the PCM.
3. 6 - This step inspects the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
4. 8 - This step inspects for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control is controlled by the PCM. The engine must be running to enable the HO2S heater.
5. 9 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Does the HO2S 1 voltage fluctuate rapidly above and below 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the HO2S 1 connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the high signal circuit of the HO2S 1 harness connector on the engine harness side to a good ground using a DMM. Is the HO2S 1 voltage within 0.425-0.500 volt? If yes, go to next step. If no, go to step 6 .
5. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit of the engine harness and the HO2S 1 low reference circuit of the engine harness. Turn ignition switch to RUN position, engine OFF. Observe the HO2S 1 voltage using a scan tool. Is the HO2S 1 voltage less than 25 mV? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Disconnect both PCM harness connectors. Measure the resistance of each of the following circuits using a DMM: HO2S 1 high signal circuit between HO2S connector and the PCM connector HO2S 1 low reference circuit between HO2S connector and the PCM connector Low reference loop between PCM harness connector C1 terminal No. 29 and PCM harness connector C2 terminal No. 80. Is the resistance of each circuit less than 5 ohms? If yes, go to step 11 . If no, go to next step.
7. Repair the circuit that measured a high resistance or an open? After repair, go to step 14 .
8. Remove the jumpers from the HO2S 1 terminals. Connect a test light between the HO2S heater ignition voltage circuit and heater low control circuit terminals on the engine harness side. Start the engine. Does the test light illuminate? If yes, go to next step. If no go to «DTC P0135: HO2S 1 HEATER PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0135-ho2s-1-heater-performance) .
9. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
10. Test for an intermittent and for a poor connection at the HO2S 1 harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the PCM harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace HO2S 1. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0135: HO2S 1 HEATER PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The PCM controls the HO2S 1 heater low control circuit with a low side driver. The HO2S 1 heater diagnostic monitors the current draw through the HO2S 1 low side driver when the engine is running. If the PCM detects that the HO2S 1 heater low control circuit current level is not within the calibrated range, DTC P0135 will set.

The HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The Engine Run Time parameter is more than 3 minutes.
3. The ECT Sensor parameter is more than 158°F (70°C).
4. The Engine Speed parameter is 650-2500 RPM.
5. The MAF sensor parameter is 4-26 g/s.
6. The system voltage is 9-18 volts.

The PCM detects that the 02 Heater Current parameter is less than 0.25 amp or more than 0.90 amp.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Use a scan tool to clear the MIL and the DTC.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Observe the HO2S 1 heater current parameter using a scan tool. Allow the HO2S 1 heater current parameter to stabilize. Is the amperage 0.25-0.85 amp? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Disconnect the HO2S 1 harness connector. Turn ignition switch to RUN position, engine OFF. Probe the HO2S heater ignition 1 voltage circuit, on the engine harness side, using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 1 heater ignition 1 voltage fuse for an open. Is the fuse open? If yes, go to step 10 . If no, go to step 15 .
6. Turn ignition switch to OFF position. Connect a test light between the HO2S ignition 1 voltage circuit and the HO2S heater low control circuit, on the engine harness side connector. Start the engine. Does the test light illuminate? If yes, go to next step. If no, go to step 8 .
7. Leave the test light connected between the HO2S 1 heater ignition voltage circuit and the HO2S 1 heater low control circuit. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Does the test light illuminate? If yes, go to step 9 . If no, go to step 10 .
8. Turn ignition switch to OFF position. Disconnect the PCM connector containing the HO2S 1 heater low control circuit. Measure the resistance from the HO2S heater low control circuit between the PCM harness connector and the HO2S harness connector using a DMM. Is the resistance 0-5 ohms? If yes, go to step 13 . If no, go to step 14 .
9. Test the HO2S 1 heater low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
10. Test the HO2S 1 heater ignition voltage circuit for a short to ground and replace the fuse. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
11. Measure the resistance from the ignition 1 voltage circuit of the sensor side of the HO2S harness connector to each of the following circuits: The HO2S low reference circuit. Ground. Is the resistance less than 5 ohms? If yes, go to step 16 . If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
12. Test for an intermittent and for a poor connection at the HO2S 1 harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
13. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
14. Repair the open or high resistance in the HO2S heater low control circuit. After repair, go to step 18 .
15. Repair the open or high resistance in the HO2S ignition 1 voltage circuit. After repair, go to step 18 .
16. Replace the HO2S 1. After repair, go to step 18 .
17. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
18. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
19. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed. If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0137: HO2S 2 CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. If the PCM detects that the HO2S 2 voltage remains below a calibrated amount for an excessive amount of time, DTC P0137 will set.

The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The system voltage is 9-18 volts.
3. The Loop Status parameter is closed.
4. The Air Fuel Ratio parameter ratio is between 12-16.5.
5. The TP sensor parameter is 3-40 percent.

The PCM detects that the HO2S 2 signal voltage remains below 74 mV during closed loop operation for more than 2.5 minutes or the PCM detects that the HO2S 2 signal voltage remains below 550 mV during Power Enrichment (PE) mode for more than 16 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze Frame/Failure Records. Observe the Heated Oxygen Sensor (HO2S) 2 voltage parameter using a scan tool. Vary the engine speed from idle to 3000 RPM several times within 5 seconds. Is the HO2S 2 voltage less than 30 mV? If yes, go to step 5 . If no, go to next step.
3. Is the HO2S 2 voltage 425-475 mV? If yes, go to «DTC P0140: HO2S 2 CIRCUIT - INSUFFICIENT ACTIVITY»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0140-ho2s-2-circuit) . If no, go to next step.
4. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the scan tool indicate that this DTC failed this ignition? If yes, go to next step. If no, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Turn ignition switch to OFF position. Disconnect the HO2S 2 harness connector. Connect a 3-amp fused jumper wire between the HO2S 2 low signal circuit, at the engine harness side, and a good ground. Turn ignition switch to RUN position, engine OFF. Observe the HO2S 2 voltage parameter using a scan tool. Is the HO2S voltage less than 30 mV? If yes, go to next step. If no, go to step 7 .
6. Check the HO2S 2 high signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step. The HO2S 2 may be detecting a lean exhaust condition. Check for one of the following conditions: HO2S connector water intrusion. An exhaust leak between the HO2S 2 and engine. Vacuum leaks. Incorrect fuel pressure. Lean fuel injectors. An inaccurate MAF sensor.
7. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
8. Test for an intermittent and for a poor connection at the HO2S 2 harness connector. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the Powertrain Control Module (PCM) harness connectors. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace the HO2S 2. After repair, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0138: HO2S 2 CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. If the PCM detects that the HO2S 2 voltage remains below a calibrated amount for an excessive amount of time, DTC P0138 will set.

The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The Air Fuel Ratio parameter is 14.5:1-14.8:1.
3. The TP sensor parameter is 3-40 percent.
4. The system voltage is 9-18 volts.

The PCM detects that the HO2S 2 voltage is more than 920 mV for more than 2 minutes during Closed Loop operation or the PCM detects that the HO2S 2 voltage is more than 200 mV during Decel Fuel Cut-Off (DFCO) for more than 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 3 - A normally functioning HO2S 2 voltage signal will fluctuate above and below the bias voltage amount. The action in the test step should result in a visible reaction from the HO2S 2 output.
2. 5 - A voltage reading other than bias voltage in this step indicates a short circuit condition in the high signal circuit.
3. 7 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0140 also set? «DTC P0140: HO2S 2 CIRCUIT - INSUFFICIENT ACTIVITY»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0140-ho2s-2-circuit) . If yes, go to next step.
3. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 2 voltage parameter using a scan tool. Vary the engine speed from idle to 3000 RPM several times within 5 seconds. Is the HO2S 2 voltage more than 920 mV? If yes, go to step 5 . If no, go to next step.
4. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the scan tool indicate that this DTC failed this ignition? If yes, go to next step. If no, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Turn ignition switch to OFF position. Disconnect HO2S 2 sensor harness connector. Connect a 3-amp fused jumper wire between the HO2S 2 low signal circuit and a good ground. Turn ignition switch to RUN position, engine off. Using a Digital Multimeter (DMM), measure the voltage of the HO2S 2 high signal circuit on the PCM side. Does the voltage measure 350-550 mV? If yes, go to next step. If no, go to step 7 .
6. Check the HO2S 2 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 9 .
7. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
8. Check for poor connections at the HO2S 2 harness connector. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 10 .
9. Check for poor connections at the PCM harness connectors. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace HO2S 2. When complete, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay.

DTC P0140: HO2S 2 CIRCUIT - INSUFFICIENT ACTIVITY

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. If the PCM detects that the HO2S 2 voltage remains below a calibrated amount for an excessive amount of time, DTC P0140 will set.

The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The engine run time parameter is longer than 2 minutes.
3. The system voltage is 9-18 volts.
4. The diagnostic runs once per trip.
5. There is a Throttle Position (TP) sensor angle change of more than 8 percent at least 5 times during the test period.

The PCM detects that the HO2S 2 signal voltage remains between 408-512 mV for more than 5 minutes.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 2 voltage signal will fluctuate above and below the bias voltage amount. The action in the test step should result in a visible reaction from the HO2S 2 output.
2. 4 - A voltage reading other than the specified amount in this step indicates an open circuit condition in one of the signal circuits or the PCM.
3. 5 - This step inspects for an open circuit condition in the signal circuits, independent of the PCM.
4. 7 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 2 voltage parameter using a scan tool. Vary the engine speed from idle to 3000 RPM several times within 5 seconds. Does the HO2S 2 voltage fluctuate above and below 375-475 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to RUN position. Disconnect the HO2S 2 harness connector. Connect a 3-amp fused jumper wire between the HO2S 2 low signal circuit of the engine harness and a good ground. Connect a 3-amp fused jumper wire between the HO2S 2 high signal circuit of the engine harness and a good ground. Turn ignition switch to RUN position, engine OFF. Observe the HO2S 2 voltage parameter using a scan tool. Is the HO2S 2 voltage less than 25 mV? If yes, go to step 7 . If no, go to next step.
5. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM). Measure the resistance of the HO2S 2 high signal circuit. Measure the resistance of the HO2S 2 low signal circuit. Is the resistance 0-5 ohms? If yes, go to step 9 . If no, go to next step.
6. Repair the signal circuit that has an open or high resistance. After repair, go to step 12 .
7. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. «EMISSION SYSTEMS & SUB-SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__emission-systems-sub-systems) in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
8. Test for an intermittent and for a poor connection at the HO2S 2 harness connector. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the PCM harness connector. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step 11 .
10. Replace the HO2S 2. After repair, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0141: HO2S 2 HEATER PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S 2 heater performance diagnostic will only run from a cold start and only once per key cycle. The HO2S 2 heater circuit is energized anytime the ignition key is in the RUN position.

If the PCM detects that the HO2S 2 heater takes too long to heat, based on the HO2S 2 signal voltage, DTC P0141 will set. The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The Start-Up IAT Sensor parameter is less than 95°F (35°C).
3. The Start-Up ECT Sensor parameter is less than 95°F (35°C).
4. The Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensor parameters are within 11°F (6°C) of each other at start-up.
5. The system voltage is 9-18 volts.

The PCM detects that the HO2S 2 voltage remains within 74 mV of the bias voltage, about 450 mV, for a longer amount of time than necessary. The amount of time ranges between 100-130 seconds depending on ECT at start-up, and the average Mass Airflow (MAF) since start-up.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - The HO2S 2 should be allowed to cool before performing this test. The HO2S 2 is cool enough if the voltage output is stable at bias or about 450 mV. If the HO2S 2 heater is functioning, the signal voltage will gradually change as the sensor element warms. If the heater is not functioning, the HO2S 2 signal will remain near the 450 mv bias voltage or show very little activity.
2. 4 - This step ensures that the ignition voltage circuit to the HO2S 2 is not open or shorted. The test light must be connected to a good ground, independent of the HO2S system.
3. 6 - This test must not be performed until the HO2S 2 heater has cooled and stabilized for at least 15 minutes. Heater resistance is typically about 5 ohms at room temperature.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine OFF. Monitor the HO2S 2 voltage using a scan tool. Does the HO2S 2 voltage go above or below the previously stabilized voltage by at least as much as 100 mV within 2 minutes? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the HO2S 2 harness connector. Turn ignition switch to RUN position, engine OFF. Connect a test light between the HO2S 2 heater ignition voltage circuit at the engine harness side of the HO2S connector and a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 7 .
5. Turn ignition switch to OFF position. Connect a test light between the HO2S 2 heater ignition voltage circuit, of the engine harness, and the HO2S 2 heater ground circuit of the engine harness. Turn ignition switch to RUN position, engine OFF. Does the test light illuminate? If yes, go to next step. If no, go to step 10 .
6. Turn ignition switch to OFF position. Leave the HO2S connector disconnected. Allow the engine to cool for at least 15 minutes. Measure the resistance from the HO2S heater ignition circuit to the heater ground circuit of the HO2S. Is the resistance 2-20 ohms? If yes, go to next step. If no, go to step 11 .
7. Test the HO2S 2 heater ignition voltage circuit fuse for an open. Did you find an open fuse? If yes, go to next step. If no, go to step 9 .
8. Repair the short to ground in the HO2S 2 heater ignition voltage circuit and replace the fuse. After repair, go to step 13 .
9. Repair the open or high resistance in the HO2S 2 heater ignition voltage circuit. After repair, go to step 13 .
10. Repair the open or high resistance in the HO2S 2 heater ground circuit. After repair, go to step 13 .
11. Test for an intermittent and for a poor connection at the HO2S 2 harness connector. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
12. Replace the HO2S 2. After repair, go to next step.
13. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
14. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0171: FUEL TRIM SYSTEM LEAN

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) controls the air/fuel metering system to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during open loop and closed loop. During open loop, the PCM determines fuel delivery based on sensor signals, without Oxygen Sensor (O2S) input. During closed loop, the PCM adds oxygen sensor inputs to calculate the short and long term fuel trim, fuel delivery adjustments. If the oxygen sensors indicate a lean condition, the fuel trim values will be above zero percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below zero percent. The short term fuel trim values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, Diagnostic Trouble Code (DTC) P0171 sets.

1. DTCs P0101-P0103, P0107, P0108, P0121-P0123, P0130-P0135, P0137, P0138, P0140, P0141, P0201-P0206, P0300, P0401, P0403-P0405, P0410, P0440, P0442, P0446, P0506, P0507, P1404 or P1441 are not set.
2. The Engine Coolant Temperature (ECT) sensor parameter is 68-230°F (20-110°C).
3. The Intake Air Temperature (IAT) sensor parameter is 64-158°F (18-70°C).
4. The Manifold Absolute Pressure (MAP) sensor parameter is greater than 2.1-15.2 psi (105 kPa).
5. The vehicle speed is less than 82 MPH.
6. The engine speed is 550-4000 RPM.
7. The Mass Airflow (MAF) is between 2.8-150 g/s.
8. The fuel level sensor parameter is more than 10 percent.

1. The average long term fuel trim value is above 20 percent.
2. All of the above conditions are present for 6 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - If the conditions were not corrected, refer to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article for a possible fuel condition.
2. 6 - If the conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failures may be at fault.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Connect scan tool. Start and idle the engine at the normal operating temperature in Closed Loop. Record the long term fuel trim data. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Review the Freeze Frame/Failure Records and record the displayed data for this DTC. Does the scan tool indicate that the long term fuel trim is greater than 23 percent? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Operate the engine at idle. Using scan tool, observe the HO2S parameters. Does the scan tool indicate that the values are within 200-800 mV and fluctuating? If yes, go to next step. If no, go to step 5 .
4. Turn engine off. Visually and physically inspect the following: Vacuum hoses for splits, kinks, and proper connections. Fuel pressure. If fuel pressure is too low this DTC may set. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Check for fuel contamination. Did you find and correct the condition? If yes, go to step 7 . If no, go to step 6 .
5. Turn ignition switch to OFF position. Check for the following conditions: Check the HO2S for proper installation. Ensure that the electrical connectors and the wires are secure and not contacting the exhaust system. Test for continuity between the signal circuit and the low reference circuit. Did you find and correct the condition? If yes, go to step 7 . If no, go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
6. Operate the engine at idle. Check for the following conditions: Check for missing, loose, or leaking exhaust components forward of the HO2S. Check for vacuum leaks at the intake manifold, the throttle body and the injector "O" rings. Check the air induction system and the air intake ducts for leaks. Check the Secondary Air Injection (AIR) system for leaks, improper air delivery, and for the shut-off valve not closing. Check the crankcase ventilation system for leaks. Did you find and correct the condition? If yes, go to next step. If no, go to appropriate article in ENGINES.
7. Using the scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
8. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. The system will go lean if an injector is not supplying enough fuel.
2. A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel.
3. Fuel contamination, such as water and alcohol will effect the fuel trim.
4. Using a scan tool, review the Failure Records. If an intermittent condition is suspected, see «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0172: FUEL TRIM SYSTEM RICH

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) controls the air/fuel metering system to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during open loop and closed loop. During open loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed loop, the oxygen sensor inputs are added and used by the PCM to calculate the short and long term fuel trim (fuel delivery adjustments). If the oxygen sensors indicate a lean condition, the fuel trim values will be above zero percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below zero percent. The short term fuel trim values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments to maintain Air/Fuel Ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the Evaporative Emission (EVAP) canister is causing a rich condition. If the PCM detects an excessively rich condition, Diagnostic Trouble Code (DTC) P0172 sets.

1. DTCs P0101-P0103, P0107, P0108, P0121-P0123, P0130-P0135, P0137, P0138, P0140, P0141, P0201-P0206, P0300, P0401, P0403-P0405, P0410, P0412, P0418, P0440, P0442, P0446, P0506, P0507, P1404 or P1441 are not set.
2. The ECT sensor parameter is 68-239°F (20-115°C).
3. The IAT sensor parameter is 64-158°F (18-70°C).
4. The MAP sensor parameter is at more than 2.1-15.2 psi (15-105 kPa).
5. The vehicle speed is less than 82 MPH.
6. The engine speed is 550-4000 RPM.
7. The BARO sensor parameter is more than 10.1 psi (70 kPa).
8. The Mass Airflow (MAF) is 2.8-150 g/s.
9. The Fuel Level sensor parameter is more than 10 percent.

1. The average long term fuel trim value is below -13 percent.
2. All of the above conditions are present for 40 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - If the conditions were not corrected, refer to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article for a possible fuel condition.
2. 6 - An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a leaking regulator. If the conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Connect scan tool. Start and idle the engine at the normal operating temperature in Closed Loop. Record the Long Term Fuel Trim data. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Review the Freeze Frame/Failure Records and record the displayed data for this DTC. Does the scan tool indicate that the Long Term Fuel Trim is less than 13 percent? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Operate the engine at idle. Observe the HO2S parameters using a scan tool. Does the scan tool indicate that the values are 200-800 mV and fluctuating? If yes, go to next step. If no, go to step 5 .
4. Turn ignition switch to OFF position. Visually and physically inspect the following conditions: Blockage of the MAF sensor inlet screen. Splits or kinks in the vacuum hoses Improper connections of the vacuum hoses. Collapsed or restricted air intake duct. Dirty or restricted air filter. Objects blocking the throttle body. Did you find and correct the condition? If yes, go to step 7 . If no, go to step 6 .
5. Turn engine OFF. Check the HO2S for proper installation. Ensure that the electrical connectors and the wires are secure and not contacting the exhaust system. Did you find and correct the condition? If yes, go to step 7 . If no, go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
6. Check for the following conditions: Excessive fuel in the crankcase. Evaporative emissions of the control system. Refer to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Proper operations of the fuel pressure regulator. Go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Proper operation of the injectors. Go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to next step. If no, diagnose engine mechanical problem. Go to appropriate article in ENGINES.
7. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
8. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Fuel contamination, such as water and alcohol, will affect the fuel trim.
2. A malfunctioning Mass Airflow (MAF) sensor can cause a rich condition and set this DTC. Go to «DTC P0101: MAF SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Use a scan tool to review the Failure Records using a scan tool. If intermittent condition is suspected, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0201-P0206: INJECTOR CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Note. Last number of DTC refers to injector number that set DTC.

The Powertrain Control Module (PCM) enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. The PCM monitors the status of each driver. If the PCM detects an incorrect voltage for the commanded state of the driver, a fuel injector control circuit DTC sets.

1. The engine is running.
2. The ignition voltage is 9-18 volts.

1. The PCM detects an incorrect voltage on the fuel injector control circuit.
2. The condition exists for 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 4 - This step isolates the condition. If the test light blinks, the PCM is providing ground to the fuel injector.
2. 5 - This step tests if a ground is constantly being applied to the fuel injector.
3. 6 - This step isolates the circuit between the multi-way connector and the PCM. An open or short to voltage on the fuel injector control circuit will not allow the test light to blink.
4. 8 - This step inspects for fuel injector harness damage between the multi-way connector and the upper intake manifold. Careful inspection may isolate the condition before removal of the upper intake manifold.
5. 13 - This step isolates the circuit between the multi-way connector and the fuel injector. A short to voltage on the fuel injector control circuit will set this DTC.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Clear the DTCs using a scan tool. Idle the engine at the normal operating temperature. Monitor the misfire current counters using a scan tool. Are any of the misfire current counters incrementing? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Turn ignition switch to OFF position. Disconnect the fuel injector harness multi-way connector. Probe the ignition 1 voltage circuit of the suspect fuel injector using a test light connected to a battery voltage. Crank the engine. Does the test light blink when cranking the engine? If yes, go to step 8 . If no, go to next step.
5. Does the test light remain illuminated at all times? If yes, go to step 7 . If no, go to next step.
6. Check the control circuit of the fuel injector for an open and for a short to voltage or an open between the multi-way connector and the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 14 .
7. Check the fuel injector control circuit for a short to ground between the multi-way connector and the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
8. Check the accessible fuel injector jumper harness between the multi-way connector and the plenum for the following conditions: Poor connections at the multi-way connector. Damaged or pinched wiring. Broken wires inside the insulation. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
9. Remove the upper intake manifold. See appropriate article in ENGINES. Probe the appropriate fuel injector control circuit, fuel injector side, at the multi-way connector, using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 15 . If no, go to next step.
10. Using a DMM, test for continuity between the ignition voltage terminal and the appropriate fuel injector control circuit terminal, at the multi-way connector. Does the DMM indicate infinity? If yes, go to next step. If no, go to step 13 .
11. Test the fuel injector control circuit for an open, or poor connections at the fuel injector. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
12. Test the fuel injector ignition voltage circuit for an open between the fuel injector and splice. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
13. Test the fuel injector control circuit for a short to voltage, or a short to another circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
14. Check for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
15. Repair the short to ground in the fuel injector control circuit. After repair, go to step 18 .
16. Replace the appropriate fuel injector. After repair, go to step 18 .
17. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
18. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
19. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. A cylinder that is misfiring can also cause the misfire current counters to increment for another cylinder. Diagnose the cylinder with the highest level of misfire first.
2. Performing the Fuel Injector Coil test may help isolate an intermittent condition. See «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. For an intermittent condition, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

The Powertrain Control Module (PCM) provides ignition positive voltage to the coil side of the fuel pump relay. When the ignition switch is first turned to RUN position, the PCM energizes the fuel pump relay, which applies power to the fuel pump. The PCM enables the fuel pump relay as long as the engine is cranking or running, and crankshaft reference pulses are received. If no crankshaft reference pulses are received, the PCM de-energizes the fuel pump relay after 2 seconds. The PCM monitors the voltage on the fuel pump relay control circuit. If the PCM detects an incorrect voltage on the fuel pump relay control circuit, DTC P0230 sets.

1. The ignition switch is in RUN position.
2. The system voltage is 9-18 volts.

1. The PCM detects an incorrect voltage on the fuel pump relay control circuit.
2. The condition exists for less than one second.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

Conditions For Clearing DTC

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 4 - This step verifies that the PCM is providing voltage to the fuel pump relay.
2. 5 - This step tests for an open in the ground circuit to the fuel pump relay.
3. 6 - This step tests if voltage is constantly being applied to the fuel pump relay control circuit.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine OFF. Using a scan tool, command the fuel pump relay ON and OFF. Does the fuel pump relay turn ON and OFF with each command? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test as specified in the supporting text or as close as possible to the Freeze Frame/Failure records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the fuel pump relay. Turn ignition switch to RUN position, engine OFF. Probe the fuel pump relay control circuit using a test light connected to a good ground. Using a scan tool, command the fuel pump relay ON and OFF. Does the test light turn ON and OFF with each command? If yes, go to next step. If no, go to step 6 .
5. Connect a test light between the fuel pump relay control circuit and the relay ground circuit. Using a scan tool, command the fuel pump relay ON and OFF. Does the test light turn ON and OFF with each command? If yes, go to step 9 . If no, go to step 11 .
6. Does the test light remain illuminated with each command? If yes, go to step 8 . If no, go to next step.
7. Test the fuel pump relay control circuit for a short to ground or an open. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
8. Test the fuel pump relay control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
9. Check for poor connections at the fuel pump relay. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
10. Check for poor connections at the PCM harness connectors. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
11. Repair the relay ground circuit. After repair, go to step 14 .
12. Replace the fuel pump relay. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0300: ENGINE MISFIRE DETECTED

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) uses information from the Crankshaft Position (CKP) sensor and the Ignition Control Module (ICM) to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way Catalytic Converter (TWC) to overheat under certain driving conditions. The Malfunction Indicator Light (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

1. DTC P0101, P0102, P0103, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0336, P0341, P0502, P0503, P1106, P1107, P1114, P1115, P1121, P1122, P1336, P1351, P1352, P1361, P1362 or P1374 are not set.
2. The engine speed is 475-5850 RPM.
3. The battery voltage is 9-18 volts.
4. The Engine Coolant Temperature (ECT) sensor parameter is 21 to 257°F (-6 to 125°C).
5. The fuel level is more than 10 percent.
6. The Anti-Lock Brake System (ABS) and the traction control system are not active.
7. The transmission is not changing gears.
8. The A/C clutch is not changing states.
9. The PCM is not in fuel shut-off or decel fuel cut-off mode.
10. The PCM is not receiving a rough road signal.

The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 2 - If the actual CKP variation values are not within the learned values, the misfire counters may increment.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. Monitor all of the Misfire counters using the scan tool. Are any of the Misfire Current counters incrementing? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Are any other DTCs set? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
4. Can any abnormal engine noise be heard? If yes, diagnose engine mechanical problem. See appropriate article in ENGINES. If no, go to next step.
5. Observe the MISFIRE HISTORY CYL# parameter using a scan tool. Does more than one cylinder indicate a large count value for the MISFIRE HISTORY CYL# parameter? If yes, go to next step. If no, go to step 8 .
6. Are the Misfire History Cyl# counts indicated for companion cylinders 1/4 or 2/5 or 3/6? If yes, go to step 8 . If no, go to next step.
7. Check the following components: The vacuum hoses and seals for splits, restrictions, and improper connections. The throttle body and intake manifold for vacuum leaks. The crankcase ventilation system for vacuum leaks. See «POSITIVE CRANKCASE VENTILATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The Exhaust Gas Recirculation (EGR) system components for vacuum leaks or excessive flow. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The PCM grounds for corrosion and loose connections. The exhaust system for restrictions. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The fuel for contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
8. Turn ignition switch to OFF position. Disconnect the spark plug wire from the spark plug that corresponds to the Misfire Current counters that were incrementing. Connect Spark Tester (J 26792), or equivalent, to a good ground. Jumper the spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil. Start the engine. Does the spark jump the tester gap, and is the spark consistent? If yes, go to step 10 . If no, go to next step.
9. Remove the spark plug wire for the affected cylinder. Check the spark plug wire. Measure the resistance of the spark plug wire using a DMM. Is the spark plug wire resistance less than 700 ohms? If yes, go to «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 19 .
10. Remove the spark plug from the cylinder that indicated a misfire. Inspect the spark plug. Does the spark plug appear to be okay? If yes, go to next step. If no, go to step 12 .
11. Exchange the suspected spark plug with another cylinder that is operating properly. Operate the vehicle under the same conditions that the misfire occurred. Did the misfire move with the spark plug? If yes, go to step 18 . If no, go to next step.
12. Is the spark plug oil or coolant fouled? If yes, diagnose engine mechanical problem. See appropriate article in ENGINES. If no, go to next step.
13. Is the spark plug gas fouled? If yes, go to step 16 . If no, go to next step.
14. Does the spark plug show any signs of being cracked, worn, or improperly gapped? If yes, go to step 17 . If no, go to next step.
15. Perform the fuel injector coil test. Go to «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 20 . If no, diagnose engine mechanical problem. See appropriate article in ENGINES.
16. Perform the fuel system diagnosis. Go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 20 .
17. Replace or gap the spark plug. After repair, go to step 20 .
18. Replace the faulty spark plug. After repair, go to step 20 .
19. Replace the faulty spark plug. After repair, go to next step.
20. Was the customer concern the MIL flashing? If yes, go to step. If no, go to step 22 .
21. Operate the vehicle at 2500 RPM for 4 minutes. Operate the vehicle within the Conditions For Running Test in DTC P0420: TWC SYSTEM - LOW EFFICIENCY as specified in the supporting text. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in DTC P0420: TWC SYSTEM - LOW EFFICIENCY. Does the DTC run and pass? If yes, go to next step. If no, go to «DTC P0420: CATALYST SYSTEM - LOW EFFICIENCY»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0420-catalyst-system-low) .
22. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
23. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration: Variable thickness brake rotors. See appropriate article in BRAKES. Worn or damaged accessory drive belt. See appropriate COOLING SYSTEM SPECIFICATIONS & DRIVE BELT ROUTING article.
2. Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.

DTC P0325: KNOCK SENSOR PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Knock Sensor (KS) produces an alternating current voltage at all engine speeds and loads. The Powertrain Control Module (PCM) then adjusts the spark timing based on the amplitude and on the frequency of the KS signal. The PCM uses the KS signal to calculate the average voltage and assigns a voltage value. The PCM inspects the KS and the related wiring by comparing the actual knock signal to the assigned voltage range. A normal KS signal should remain out of the assigned voltage range. This DTC will set if the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system.

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0336, P0341, P0502, P0503, P1114, P1115, P1121, P1122 or P1336 are not set.
2. The engine speed is 1000-5000 RPM.
3. The throttle angle is more than 15 percent.
4. The engine load is more than 45 percent.
5. The ECT sensor parameter is more than 140°F (60°C).
6. The maximum spark retard is less than 15 degrees.
7. The system voltage is more than 9 volts.
8. The engine run time is more than 30 seconds.

1. The PCM detects a malfunction in the KS diagnostic circuitry which will not allow proper diagnosis of the KS circuit.
2. Above condition exists for at least one second.

1. PCM will illuminate the Malfunction Indicator Light (MIL) during the second consecutive trip in which the diagnostic test has run and failed.
2. PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

1. PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. Use scan tool to clear the DTCs.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close as possible to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
4. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
5. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0327: KNOCK SENSOR CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Knock Sensor (KS) system enables the Powertrain Control Module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS is located on the intake side of the engine block. The KS produces an AC voltage signal that varies depending on the vibration level during engine operation. The PCM adjusts the spark timing based on the amplitude and frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses the KS signal to calculate the average voltage and then assigns a voltage range value. The PCM should monitor a normal KS signal within the voltage range. If the PCM detects the KS signal outside of the voltage range, or the KS signal is not present, this DTC sets.

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0336, P0341, P0502, P0503, P1114, P1115, P1121, P1122 or P1336 are not set.
2. The engine speed is between 1000-5000 RPM.
3. The engine has been running for a minimum of 30 seconds.
4. The throttle angle is more than 15 percent.
5. The engine load is more than 45 percent.
6. The ECT sensor parameter is more than 140°F (60°C).
7. The maximum spark retard is less than 15 degrees.
8. The ignition voltage is more than 9 volts.

1. The PCM detects a KS signal voltage within the average voltage range for at least 10 seconds.
2. The engine run time is more than 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 3 - A fault in the 24X CKP sensor 12 volt reference circuit or the CMP sensor can cause this DTC to set.
2. 6 - Tapping on the engine block will simulate an engine knock.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Monitor the Diagnostic Trouble Code (DTC) information using the scan tool. Does the scan tool display any other DTCs set? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
3. Monitor the 24X Crank Sensor parameter using the scan tool. Is the 24X Crank Sensor parameter incrementing? If yes, go to next step. If no, go to «DTC P0336: CRANKSHAFT POSITION SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0336-crankshaft-position-sensor-performance) .
4. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Disconnect the KS harness connector. Set the DMM to the 400 k/ohm scale. Measure the resistance from the KS signal terminal to a good ground using the DMM. Is the resistance 93-107 k/ohms? If yes, go to next step. If no, go to step 10 .
6. With the DMM still connected, set the DMM to the 400 mV AC hertz scale. Tap on the engine block with a nonmetallic object near the KS while observing the signal indicated on the DMM. DO NOT tap on plastic engine components. Is any signal indicated on the DMM while tapping on the engine block near the KS? If yes, go to next step. If no, go to step 10 .
7. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Check the KS signal circuit and the KS low reference circuit for an open, high resistance, short to voltage or short to ground. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
8. Test for an intermittent and for a poor connection at the KS. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
9. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace KS. After repair, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. Using scan tool, clear the DTCs. Turn the ignition OFF for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Check the KS for physical damage. A KS that is dropped or damaged may cause a DTC to set.
2. Check the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set. The KS should be free of thread sealant. The KS mounting surface should be free of burrs, casting flash, and foreign material.
3. The KS must be clear of hoses, brackets, and engine electrical wiring.
4. For an intermittent condition, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0336: CRANKSHAFT POSITION SENSOR PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The circuit uses 2 different types of Crankshaft Position (CKP) sensors. The CKP sensor "B" is connected directly to the Ignition Control Module (ICM), and consists of the following circuits

1. The CKP 1 sensor signal circuit.
2. The low reference circuit.

The CKP sensor A connects directly to the Powertrain Control Module (PCM), and consists of the following circuits

1. The 12-volt reference circuit.
2. The medium resolution engine speed signal circuit.
3. The low reference circuit.

If the PCM detects an incorrect number of CKP pulses, DTC P0336 sets.

The engine is running, and the 3X reference pulses have been received for a minimum of 3 seconds.

The ratio of 24X reference pulses to 3X reference pulses received by the PCM is incorrect.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - If you were sent here from DTC P0327, proceed with DTC P0336 Diagnostic even if DTC P0336 has not failed this ignition.
2. 8 - The 24X RPM on the scan tool should change each time the medium resolution engine speed signal circuit is touched.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Observe the 24X parameter using a scan tool. Does 24X RPM vary with engine speed up to approximately 1600 RPM? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test or as close to the Freeze Frame/Failure Records data observed. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Turn ignition switch to OFF position. Disconnect the CKP sensor "A" connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the CKP sensor "A" 12-volt reference circuit to a good ground using the DMM. Does the voltage measure near battery voltage? If yes, go to step 6 . If no, go to next step.
5. Test the CKP sensor "A" 12-volt reference circuit for the following conditions: An open. A short to ground. High resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 12 .
6. Connect a test light to positive battery voltage. Touch the CKP sensor "A" low reference circuit. Does test light illuminate? If yes, go to step 8 . If no, go to next step.
7. Test the CKP sensor "A" low reference circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
8. Observe the 24X RPM using a scan tool. Connect a 5-amp fused jumper wire to battery positive voltage, momentarily touch the medium resolution engine speed signal circuit 5 times for a duration of one second each. Does 24X RPM change each time the signal circuit is touched? If yes, go to step 13 . If no, go to next step.
9. Did the fuse in the jumper wire open? If yes, go to step 11 . If no, go to next step.
10. Test the CKP sensor "A" medium resolution engine speed signal circuit for the following conditions: An open. A short to voltage. High resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 12 .
11. Test the medium resolution engine speed signal circuit of the CKP sensor "A" for a short to ground. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 12 .
12. Test for an intermittent or for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 14 .
13. Test for an intermittent or for a poor connection at the 24X CKP sensor. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 15 .
14. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to step 16 .
15. Replace CKP sensor "A". After repair, go to next step.
16. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
17. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0336 can be caused by secondary components leaking high voltage into the ICM. Check for the following conditions

1. Incorrect harness routing near the secondary ignition components.
2. Ignition coil arcing to wiring harness or Ignition Control Module (ICM). Check ignition coils for cracks, for carbon tracking, or for other signs of damage.
3. Secondary ignition wires arcing to the wiring harness.
4. For an intermittent, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0341: CMP SENSOR CIRCUIT PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

During cranking, the Ignition Control Module (ICM) monitors the 7X Crankshaft Position (CKP) sensor signal. Once the engine starts the ICM determines spark synchronization, by the Camshaft Position (CMP) sensor pulses. The Powertrain Control Module (PCM) constantly monitors the number of pulses on the CMP signal circuit and compares the number of CMP pulses to the number of 24X reference pulses and the number of 3X reference pulses being received. If the PCM receives an incorrect number of pulses on the CMP signal circuit, DTC P0341 will set.

The engine is running.

The Camshaft Position (CMP) sensor reference pulse is not detected during every engine revolution.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Observe the CMP sensor signal present parameter using a scan tool. Does the scan tool indicate the CMP sensor signal is present? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC reset? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Turn ignition switch to OFF position. Remove the power steering pump. Disconnect the CMP sensor harness connector. Turn ignition switch to RUN position, engine OFF. Probe the 12-volt reference circuit of the CMP sensor harness connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 8 .
5. Turn ignition switch to OFF position. Jumper the CMP circuits from the CMP sensor to the CMP sensor harness connector. Turn ignition switch to RUN position, engine OFF. Measure the Voltage Drop from the low reference circuit of the CMP sensor to a good ground using a DMM. Is the voltage more than 0.2 volt? If yes, go to step 9 . If no, go to next step.
6. Remove the jumpers from the CMP circuits. Start the engine. Observe the CMP sensor signal on the scan tool. Momentarily and repeatedly probe the signal circuit of the CMP sensor using a test light connected to battery voltage. Does the CMP sensor signal change when the test light contacts the signal circuit? If yes, go to step 12 . If no, go to next step.
7. Turn ignition switch to RUN position, engine OFF. Probe the signal circuit of the CMP sensor harness connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 11 . If no, go to step 10 .
8. Test the CMP 12-volt reference circuit between the CMP sensor and the PCM for an open or for high resistance. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
9. Test the CMP Low reference circuit between the CMP sensor and the PCM for an open or high resistance. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
10. Test the CMP signal circuit between the CMP sensor and the PCM for a open or for a short to ground. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
11. Test the CMP signal circuit between the CMP sensor and the PCM for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
12. Test for an intermittent and for poor connections at the CMP harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 14 .
13. Test for an intermittent and for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
14. Remove the CMP sensor. Visually inspect the CMP sensor for physical damage and for loose or improper installation. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
15. Visually inspect the CMP sensor reluctor wheel for damage. If the CMP reluctor wheel is damaged, diagnose mechanical problem. Go to appropriate article in ENGINES. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
16. Replace CMP sensor. After repair, go to step 18 .
17. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
18. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
19. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The following conditions may cause this DTC to set

1. Incorrect harness routing near secondary ignition components.
2. Ignition coil arcing to wiring harness or ICM. Check the ignition coils for cracks, for carbon tracking, or for other signs of damage.
3. Camshaft reluctor wheel damage.
4. The sensor coming in contact with the reluctor wheel.
5. Foreign material passing between the sensor and the reluctor wheel.
6. Excessive camshaft end-play.
7. If condition is determined to be intermittent, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0401: EGR FLOW INSUFFICIENT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) tests the Exhaust Gas Recirculation (EGR) system during deceleration. The PCM does this by momentarily commanding the EGR valve to open while monitoring the signal circuit of the Manifold Absolute Pressure (MAP) sensor. When the EGR valve is opened, the PCM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the PCM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow test counts required to exceed the fail threshold may vary according to the amount of detected EGR flow error.

Normally, the PCM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the PCM will allow up to twelve EGR flow test counts during the first ignition cycle following a code clear event. Between nine and twelve EGR flow test counts should be sufficient for the PCM to determine adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error, DTC P0401 sets.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0336, P0403, P0404, P0502, P0503, P0506, P0507, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, P1374 or P1404 are not set.
2. The Ignition 1 signal parameter is 11-18 volts.
3. The AC Relay Command parameter does not change.
4. The Current Gear parameter does not change.
5. The Intake Air Temperature (IAT) sensor parameter is 32-212°F (0-100°C).
6. The Engine Coolant Temperature (ECT) sensor parameter is more than 167°F (75°C).
7. The Engine Speed parameter is 1050-1400 RPM.
8. The Manifold Absolute Pressure (MAP) sensor parameter is 15-70 kPa.
9. The Mass Airflow (MAF) sensor parameter does not change more than 2 grams per second.
10. The Barometric Pressure (BARO) parameter is more than 74 kPa.
11. The Throttle Position (TP) sensor parameter is less than one percent.
12. The Vehicle Speed sensor parameter is more than 30 MPH during deceleration.
13. The Idle Air Control (IAC) position parameter does not change more than 5 counts while the above conditions are met.
14. The vehicle will need to be driven more than 50 MPH, and then allowed to decelerate. When the vehicle is decelerating, while meeting all of the criteria listed above, the PCM will enable the EGR flow test to run. As the EGR flow test is running, you will see the desired EGR position parameter and the EGR position sensor parameter on the scan tool momentarily change from zero to a calibrated value above zero. Additionally, the EGR flow test count parameter on the scan tool will increment when each EGR flow test is completed.

The MAP changes monitored by the PCM during the EGR flow tests indicate an insufficient amount of EGR flow.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 2 - MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0107 or P0108 also set? If yes, diagnose appropriate DTC. Go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no other DTCs are set, go to next step.
3. Check the exhaust system for leaks, restrictions, and for modification of Original Equipment Manufacture (OEM) parts. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 7 . If no, go to next step.
4. Check for a vacuum leak between the EGR valve and the intake manifold. Did you find and correct the condition? If yes, go to step 7 . If no, go to next step.
5. Remove the EGR valve. Check the EGR valve pintle and the EGR valve passages for leaks or for restrictions. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 7 . If no, go to next step.
6. Remove the EGR valve inlet pipe from the exhaust manifold. Check the exhaust manifold EGR port and the EGR valve pipe for a restriction. Did you find and correct the condition? If yes, go to step 7 . If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
7. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
8. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

Check for the following conditions

1. A vacuum restriction to the MAP sensor. A skewed MAP sensor reading can cause the PCM to read incorrect MAP changes during the EGR flow test.
2. An engine that is running poorly due to a mechanical condition such as worn piston rings, worn camshaft, etc. These types of conditions can cause low engine vacuum and thus can cause a less than expected MAP changes during the flow test.
3. Excessive back pressure in the exhaust system may cause this DTC to set. This condition can cause low engine vacuum and thus can cause a less than expected MAP changes during the EGR flow test. Possible causes of this could be a restriction in the exhaust system or non Original Equipment Manufacture (OEM) exhaust parts.
4. Exhaust system leaks can cause an insufficient amount of EGR flow through the EGR valve. This condition can cause a less than expected MAP changes due to insufficient exhaust back pressure. Possible causes of this could be a leaking exhaust system, a leaking EGR pipe or non OEM exhaust parts.
5. A restriction in the intake manifold such as carbon deposits and casting flash.

DTC P0403: EGR SOLENOID CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) controls the Exhaust Gas Recirculation (EGR) valve with a solid state device called a driver. The driver supplies the EGR solenoid with 12 volts that is Pulse Width Modulated (PWM) through the EGR solenoid high control circuit. A ground path is provided by the PCM through the EGR solenoid low control circuit. The driver has the ability to detect an electrical malfunction on the EGR solenoid control circuits. If the PCM determines that the driver has detected an electrical malfunction on one of these circuits, DTC P0403 sets.

1. The engine is cranking or running.
2. The Ignition 1 Signal parameter is 11-18 volts.

1. The PCM detects an electrical malfunction in the EGR solenoid high control circuit or the EGR solenoid low control circuit.
2. The above condition is met for more than 20 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 6 - This step tests for voltage that is constantly being applied to the EGR valve.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine OFF. Command the EGR from zero percent to 100 percent using a scan tool. Does the EGR Position Sensor parameter remain within 3 percent of the desired EGR position parameter when commanded using a scan tool? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the EGR valve. Turn ignition switch to RUN position, engine OFF. Probe the EGR solenoid high control circuit using a test light connected to a good ground. Command the EGR valve from 0-10 percent and from 10-0 percent using a scan tool. Does the test light turn ON at 10 percent and OFF at zero percent when commanded using a scan tool? If yes, go to next step. If no, go to step 6 .
5. Connect a test light between the EGR solenoid high control circuit and the EGR solenoid low control circuit. Command the EGR valve from 0-10 percent using a scan tool. Does the test light illuminate? If yes, go to step 10 . If no, go to step 9 .
6. Does the test light remain illuminated when the EGR valve is commanded to zero percent using a scan tool? If yes, go to step 8 . If no, go to next step.
7. Test the EGR solenoid high control circuit for a short to ground or for an open. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
8. Test the EGR solenoid high control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
9. Test the EGR solenoid low control circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
10. Test for an intermittent and for a poor connection at the EGR valve. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace the EGR valve. After repair, go to step 14 .
13. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
14. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0404: EGR OPEN POSITION PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Exhaust Gas Recirculation (EGR) valve position sensor is monitored by the Powertrain Control Module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. The PCM compares the EGR Position Sensor parameter with the desired EGR position parameter when the valve is commanded open or closed. If the PCM detects a calibrated difference between the EGR Position Sensor parameter and Desired EGR Position parameter for a calibrated amount of time, DTC P0404 sets.

1. The Ignition 1 Signal parameter is 11-18 volts.
2. The EGR valve is commanded to open.

1. The difference between the EGR position sensor parameter and the desired EGR position parameter is more than 15 percent.
2. The above condition is met for more than 20 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0403 or P0405 also set? If yes, diagnose appropriate DTC. Go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no other DTCs are set, go to next step.
3. Turn ignition switch to RUN position, engine OFF. Command the EGR valve from zero percent to 100 percent using a scan tool. Does the EGR position sensor parameter remain within 15 percent of the desired EGR Position parameter when commanded using a scan tool? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Turn ignition switch to OFF position. Disconnect the EGR valve. Turn ignition switch to RUN position, engine OFF. Observe the EGR position sensor parameter using a scan tool. Is the EGR position sensor parameter less than one percent? If yes, go to next step. If no, go to step 11 .
6. Connect a test light between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve Does the test light illuminate? If yes, go to next step. If no, go to step 8 .
7. Connect a 3 amp fused jumper wire between the 5-volt reference circuit of the EGR valve and the EGR valve position signal circuit. Observe the EGR POSITION SENSOR parameter on the scan tool. Is the EGR Position Sensor parameter more than 99 percent? If yes, go to step 9 . If no, go to step 13 .
8. Connect a test light between the 5-volt reference circuit of the EGR valve and a good ground. Does the test light illuminate? If yes, go to step 12 . If no, go to step 14 .
9. Command the EGR valve to 100 percent using a scan tool. Measure the voltage from the EGR high control circuit to a good ground. Note the results in volts as "supply voltage". Connect a jumper wire between the EGR low control circuit and the corresponding terminal on the EGR valve. Connect a DMM between the EGR high control circuit and the corresponding terminal on the EGR valve. Measure the note and current draw in amps. Remove the DMM from the EGR high control circuit. Connect a jumper wire between the EGR high control circuit and the corresponding terminal on the EGR valve. Connect a DMM in parallel between the EGR high control circuit and a good ground. Measure the voltage drop in volts and note as "load voltage drop". Subtract the load voltage drop from the supply voltage then divide the answer by the current draw. The result is the amount of resistance in the EGR high control circuit. Is the calculated resistance more than 3 ohms? If yes, go to step 15 . If no, go to next step.
10. Connect a DMM in parallel between the EGR low control circuit and a good ground. Measure the voltage drop in volts and not as "low control voltage drop". Divide the low control voltage drop by the current draw. The result is the amount of resistance in the low control circuit. Is the calculated resistance more than 3 ohms? If yes, go to step 16 . If no, go to step 17 .
11. Test the EGR valve position signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
12. Test the low reference circuit of the EGR valve for an open or for high resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
13. Test the EGR valve position signal circuit for the following conditions: An open. A short to ground. High resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
14. Test the 5-volt reference circuit of the EGR valve for an open or for high resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
15. Test the high control circuit of the EGR valve for resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
16. Test the low control circuit of the EGR valve for resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 18 .
17. Test for an intermittent and for a poor connection at the EGR valve. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 19 .
18. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 20 . If no, go to next step.
19. Replace the EGR valve. After repair, go to step 21 .
20. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
21. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
22. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Check for excessive deposits on the EGR pintle or seat. Check for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
2. If condition is determined to be intermittent, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0405: EGR POSITION SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Exhaust Gas Recirculation (EGR) valve position sensor is monitored by the Powertrain Control Module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. If the EGR valve position sensor signal voltage is pulled below a calibrated value, DTC P0405 sets.

The Ignition 1 Signal parameter is 11-18 volts.

1. The EGR Position Sensor parameter is less than 0.35 volts.
2. The above condition is met for more than 20 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 9 - By disconnecting each component one at a time, the component that is pulling the 5-volt reference circuit low will be revealed.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P1635 also set? If yes, go to «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) or «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) . If no, go to next step.
3. Turn ignition switch to RUN position, engine OFF. Observe the EGR POSITION SENSOR voltage parameter using a scan tool. Is the EGR Position Sensor voltage parameter less than 0.35 volt? If yes, go to step 5 . If no, go to next step.
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Turn ignition switch to OFF position. Disconnect the EGR valve. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the EGR valve and the EGR valve position signal circuit. Turn ignition switch to RUN position, engine OFF. Observe the EGR POSITION SENSOR parameter using a scan tool. Is the EGR Position Sensor parameter more then 99 percent? If yes, go to step 11 . If no, go to next step.
6. Disconnect the 3-amp fused jumper wire. Connect a test light between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve Does the test light illuminate? If yes, go to step 10 . If no, go to next step.
7. Test the 5-volt reference circuit of the EGR valve for an open or for high resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
8. Test all 5-volt reference circuits for a short to ground. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
9. Connect a DMM between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve. Observe the voltage while disconnecting all sensors, one at a time, that use a 5-volt reference circuit. A change in voltage indicates the faulty component. Replace that component as necessary. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 12 .
10. Test the EGR valve position signal circuit for the following conditions: A short to ground. An open. High resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 12 .
11. Test the EGR valve position signal circuit for a short to the EGR solenoid high control circuit. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 13 .
12. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 15 .
13. Test for an intermittent and for a poor connection at the EGR valve. Did you find and correct the condition? If yes, go to step 16 . If no go to next step.
14. Replace the EGR valve. After repair, go to step 16 .
15. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
16. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
17. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0420: CATALYST SYSTEM - LOW EFFICIENCY

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx), a 3-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting the NOx to nitrogen. The converter also has the ability to store excess oxygen and release the stored oxygen to promote these reactions. This Oxygen Storage Capacity (OSC) is a measurement of the catalysts ability to control emissions. The Powertrain Control Module (PCM) monitors this process using a Heated Oxygen Sensor (HO2S) located in the exhaust stream past the three-way converter. When the catalyst is functioning properly, the HO2S 2 is slow to respond to a large change in the HO2S 1 signal. When the HO2S 2 responds quickly to a large change in the HO2S 1 signal, the OSC and efficiency of the catalyst is considered to be bad and if subsequent tests also indicate a failure DTC P0420 will set.

Meet the conditions for engine warm up. Use the scan tool catalyst data list to verify the following

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201-P0206, P0300, P0325, P0327, P0336, P0341, P0401, P0403, P0404, P0405, P0410, P0412, P0418, P0440, P0442, P0443, P0446, P0449, P0502, P0503, P0506, P0507, P1133, P1134, P1336, P1351, P1352, P1361, P1374 or P1441 are not set.
2. The engine has been running more than 10 minutes.
3. The Engine Coolant Temperature (ECT) is above 158°F (70°C) and below 255°F (124°C).
4. The BARO sensor parameter is more than 75 kPa.
5. The vehicle is in a closed loop operation.
6. The Intake Air Temperature (IAT) is above -4°F (-20°C), and is less than 212°F (100°C).
7. The battery voltage above 10.7 volts.

Warm the catalyst

1. Fully open the hood.
2. The vehicle is in Park (A/T) or in Neutral (M/T).
3. Set the parking brake.
4. Press and hold the service brake.
5. Each time the engine is started the diagnostic can run up to 18 times. After the 10 minute run time and before the diagnostic runs the first time, the engine must run an additional 5 minutes between 1500-2500 RPM. Any additional tests on the same key cycle, the engine speed must be between 1500-2500 RPM for 1 minute.
6. To activate the diagnostic, return to idle and put the vehicle in drive (depress the clutch for manual).

Test the catalyst.

1. Transmission is in Drive (A/T) or Neutral (M/T with clutch depressed).
2. Verify if DTC P0420 has passed or failed this key cycle using the scan tool.

The PCM determines that the catalysts oxygen storage capacity is below a threshold considered acceptable.

1. The PCM illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame/Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 1 - The Diagnostic System Check-Engine Controls prompts the technician to complete some basic tests and store the Freeze Frame/Failure Records data on the scan tool, if applicable.
2. 2 - If any component DTCs are set, diagnose those DTCs first. A fault in a component can cause the converter to appear degraded or may have caused the failure.
3. 3 - Clearing the DTCs allows the catalyst test to be tested up to 18 times and completed up to 6 times this ignition cycle. If the A/C is not turned OFF the diagnostic may not run. The engine must be warm. Warm the converter by raising the engine speed above idle for the specified time prior to each attempted test. Has the DTC passed or failed this ignition cycle? If the DTC does not pass or fail look for a possible reason that would cause the test to abort.
4. 4 - This step includes tests for conditions that can cause the 3-way converter to appear degraded. Repair any conditions before proceeding with this test.
5. 9 - If the 3-way converter needs to be replaced, ensure that another condition which could damage the converter is not present. These conditions may include misfire, leaking or plugged fuel injectors, high engine oil or coolant consumption, retarded spark timing, or weak spark. Correct any possible causes of converter damage before replacing the converter.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Are any other DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
3. Turn the A/C OFF. Start the engine and wait until the vehicle is fully warmed up at least 10 minutes, then above 1500 RPM for 5 additional minutes. (One minute for each additional attempt at 1500 RPM on same key cycle). The vehicle may be driven for the 5 minute run time. Fully open the hood. Operate the vehicle within the Conditions For Running Test as specified in the supporting text. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle the test may be aborted. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . The test may need to be completed up to 6 times to pass or fail. Does the DTC reset? If yes, go to next step. If no, system is okay at this time.
4. Check the 3-way catalytic converter for the following damage: Dents. Severe discoloration caused by excessive temperatures. Holes. Internal rattle caused by damaged catalyst substrate. Verify that the 3-way catalytic converter is a proper original equipment manufacturer part. Did your inspection reveal a condition? If yes, go to step 9 . If no, go to next step.
5. Check the exhaust system for leaks. See «EXHAUST LEAKAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-leakage) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Check the exhaust system for restrictions. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find any of the conditions? If yes, go to step 7 . If no, go to next step.
6. Check the oxygen sensors and the oxygen sensor wiring harness for damage. Did you find any of the conditions? If yes, go to step 8 . If no, go to step 9 .
7. Repair the exhaust system as necessary. After repair, go to step 10 .
8. Repair as necessary. After repair, go to step 10 .
9. Replace the three way catalytic converter. After repair, go to next step.
10. Clear the DTCs using a scan tool. Turn the A/C OFF. Start the engine. Allow the engine to warm for at least ten minutes, then above 1500 RPM for 5 additional minutes. (One minute for each additional attempt at 1500 RPM on same key cycle). The vehicle may be driven for the 5 minute run time. Fully open hood. Operate the vehicle within the Conditions For Running Test, as specified in the supporting text. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle the test may be aborted. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Test may need to be completed up to 6 times to pass or fail. Does the DTC reset? If yes, go to step 4 . If no, go to next step.
11. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The PCM will NOT enable the catalyst test until following conditions are met

1. The engine idle speed is within 150 RPM of the desired idle.
2. The throttle position is 1.5 percent or less.
3. The short term integrator is between -20 to 20 percent.

The catalyst test will abort if the vehicle falls outside the conditions listed below while the test is running

1. The engine idle speed is within 300 RPM of the desired idle, or within 150 RPM for the w/67.
2. The throttle position is 1.5 percent or less.
3. The short term integrator is between -20 to 20 percent.

The catalyst test may abort due to a change in the engine load from the A/C, the coolant fan, or other components. If this condition occurs, use the scan tool to force the cooling fans ON, then return to step 2 in the test.

When using a scan tool to command the cooling fans ON, use the next list and previous list soft keys to enter the catalyst data list. If the catalyst data list is not entered this way the cooling fan control will be canceled.

1. The number of attempted tests is limited to 18 per key cycle.
2. More than 6 tests may have to be attempted to achieve 6 completed tests. An aborted test counts as an attempted test.
3. If 18 tests have been attempted, and a decision has not been made this key cycle, turn ignition switch to position OFF for 30 seconds. Start the vehicle and perform the conditions for running the DTC, including the 10 minute engine run time.
4. After returning to an idle the HO2S 1 signal may stay rich or lean for several seconds causing the test to be delayed.

If the condition is intermittent, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0440: EVAPORATIVE EMISSION SYSTEM

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The PCM tests the Evaporative Emission (EVAP) system for a large leak. The PCM monitors the Fuel Tank Pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the PCM commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the PCM commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP table.

EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1106, P1107, P1112, P1114, P1115, P1121 or P1122 are not set.
2. The engine is running.
3. The ignition voltage is 10-18 volts.
4. The Barometric Pressure (BARO) sensor parameter is more than 75 kPa.
5. The Fuel Level sensor parameter is 15-85 percent.
6. The Engine Coolant Temperature (ECT) sensor parameter is 39-86°F (4-30°C).
7. The Intake Air Temperature (IAT) sensor parameter is 39-86°F (4-30°C).
8. The start-up ECT and IAT are within 16°F (9°C) of each other.
9. The Vehicle Speed Sensor (VSS) parameter is less than 75 MPH.

The EVAP system is not able to achieve or maintain vacuum during the diagnostic test.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM will turn the Malfunction Indicator Light (MIL) OFF during the first consecutive trip in which the diagnostic has been run and passed.
2. A last test failed (current DTC) clears when the PCM turns OFF the MIL.
3. The history DTC will clear after the PCM runs and passes 40 consecutive warm up cycles with no failure.
4. The DTC can be cleared by using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - This step verifies that a failure condition is active.
2. 4 - Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
3. 6 - This step verifies proper operation of the Fuel Tank Pressure (FTP) sensor.
4. 7 - A normal operating FTP sensor should increase above 5 in. H20 and stop between 6 and 7 in. H20.
5. 9 - This step tests the EVAP purge solenoid vacuum source between the EVAP purge solenoid and the Intake manifold for restrictions or blockages.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Perform the Service Bay Test. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the Service Bay Test passed? If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If yes, go to next step.
3. Check the Evaporative Emission (EVAP) system for the following conditions: Loose, missing, or damaged service port Schrader valve. Loose, incorrect, missing, or damaged fuel fill cap A damaged EVAP purge solenoid. Raise and support the vehicle on a hoist. Check the EVAP system for the following conditions: Disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses. A damaged EVAP vent solenoid or EVAP canister. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
4. Turn ignition switch to OFF position. Connect the Evaporative Emissions System Tester (EEST) (J 41413-200) power supply clips to a known good 12-volt source. Install the Fuel Tank Cap Adapter (J 41415-40) to the fuel fill pipe. Connect the fuel fill cap to the fuel tank cap adapter. Connect the EEST nitrogen/smoke supply hose to the fuel tank cap adapter. Turn ignition switch to RUN position, engine OFF. Command the EVAP vent solenoid closed using a scan tool. Turn the nitrogen/smoke valve on the EEST control panel to SMOKE. Use the remote switch to introduce smoke into the EVAP system. Use the EVAP Service Port Vent Fitting (J 41413-VLV) to open the EVAP service port. Remove the service port vent fitting once smoke is observed. Continue to introduce smoke into the EVAP system for an additional 60 seconds. Check the entire EVAP system for exiting smoke using the High Intensity White Light (J 41413-SPT). Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step 19 . If no, go to next step.
5. Disconnect the fuel tank cap adapter from the fuel fill pipe. Install the fuel fill cap to the fuel fill pipe. Connect the EEST nitrogen/smoke supply hose to the EVAP service port. Use the remote switch to introduce smoke into the EVAP system. Check the entire EVAP system for exiting smoke using the high intensity White light. Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step 19 . If no, go to next step.
6. Use the remote switch to stop introducing smoke. Install the fuel tank cap adapter to the fuel fill pipe. Connect the EEST nitrogen/smoke supply hose to the fuel tank cap adapter. Connect the vehicle fuel fill cap to the EEST. Command the EVAP vent solenoid open using a scan tool. Compare the Fuel Tank Pressure (FTP) sensor parameter, using a scan tool, to the EEST pressure/vacuum gauge. Is the scan tool FTP sensor parameter within one in. H2O of the EEST pressure/vacuum gauge? If yes, go to next step. If no, go to step 16 .
7. Seal the EVAP system using the EVAP Purge/Seal function using a scan tool. Turn the nitrogen/smoke valve on the EEST control panel to NITROGEN. Use the EEST to pressurize the EVAP system to 10 in. H2O. Is the FTP sensor parameter more than 5 in. H2O? If yes, go to next step. If no, go to step 16 .
8. Use the remote switch to stop introducing nitrogen into the EVAP system. Increase the EVAP purge solenoid to 100 percent. Is the FTP sensor parameter less than one in. H2O? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go to next step.
9. Disconnect the EVAP purge vacuum source from the EVAP purge solenoid. Is the FTP sensor parameter less than one in. H2O? If yes, go to step 13 . If no, go to next step.
10. Disconnect the EVAP purge pipe from the EVAP purge solenoid. Is the Fuel Tank Pressure sensor parameter less than one in. H2O? If yes, go to step 13 . If no, go to next step.
11. Disconnect the EVAP purge pipe at the EVAP canister. Is the FTP sensor parameter less than one in. H2O? If yes, go to step 15 . If no, go to next step.
12. Disconnect the EVAP vapor pipe at the EVAP canister. Is the Fuel Tank Pressure sensor parameter less than one in. H2O? If yes, go to step 18 . If no, go to step 14 .
13. Repair the pinched or obstructed EVAP purge solenoid vacuum source. After repair, go to step 19 .
14. Repair the pinched or obstructed EVAP vapor pipe. After repair, go to step 19 .
15. Repair the restriction in the EVAP purge pipe. After repair, go to step 19 .
16. Replace the FTP sensor. After repair, go to step 19 .
17. Replace the EVAP purge solenoid. After repair, go to step 19 .
18. Replace the EVAP canister. After repair, go to step 19 .
19. Perform the Service Bay Test. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the Service Bay Test passed? If yes, go to next step. If no, go to step 3 .
20. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. To help locate intermittent leaks, use the Evaporative Emissions System Tester (EEST) (J 41413-200), or equivalent, to introduce smoke into the EVAP system. Move all EVAP components while observing smoke using the High Intensity White Light (J 41413-SPT), or equivalent.
2. A temporary blockage in the EVAP purge solenoid, purge pipe or EVAP canister could cause an intermittent condition. Check and repair any restriction in the EVAP system.
3. To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles using the high intensity White light.
4. Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
5. For intermittent conditions, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0442: EVAPORATIVE EMISSION CONTROL SYSTEM - SMALL LEAK DETECTED

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

This DTC tests the Evaporative Emission (EVAP) system for a small leak. The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON and the EVAP vent valve ON. This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the EVAP canister purge valve OFF, sealing the system, and monitors the FTP sensor input to determine the EVAP system vacuum decay. If the PCM detects a leak larger than a calibrated amount, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE VALVE/VENT VALVE RELATIONSHIP table.

EVAP CANISTER PURGE VALVE/VENT VALVE RELATIONSHIP

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0443, P0449, P0452, P0453, P1106, P1107, P1112, P1114, P1115, P1121 or P1122 are not set.
2. The ignition voltage is 10-18 volts.
3. The Barometric Pressure (BARO) sensor parameter is more than 75 kPa.
4. The fuel level sensor parameter is 15-80 percent.
5. The Engine Coolant Temperature (ECT) sensor parameter is 39-86°F (4-30°C).
6. The Intake Air Temperature (IAT) sensor parameter is 39-86°F (4-30°C).
7. The start up ECT and IAT are within 16°F (9°C) of each other.
8. The Vehicle Speed Sensor (VSS) is less than 75 MPH.

The EVAP system can achieve vacuum but a vacuum decay is detected during the diagnostic test.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - This step verifies that a failure condition is present.
2. 4 - Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
3. 6 - This step verifies that repairs are complete and that no other condition is present.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Perform the Service Bay Test. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to next step.
3. Check EVAP system for the following conditions: A loose, missing, or damaged service port Schrader valve. A loose, incorrect, missing, or damaged fuel fill cap. A damaged EVAP canister purge solenoid. Raise and support vehicle on hoist. Check EVAP system for the following conditions: Any disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses. A damaged EVAP canister vent solenoid or EVAP canister. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
4. Turn ignition switch to OFF position. Connect the Evaporative Emissions System Tester (EEST) (J 41413-200), or equivalent, power supply clips to a known good 12-volt source. Install the Fuel Tank Cap Adapter (J 41415-40), or equivalent, to the fuel fill pipe. Connect the fuel fill cap to the fuel tank cap adapter. Connect the EEST nitrogen/smoke supply hose to the fuel tank cap adapter. Turn ignition switch to RUN position, engine OFF. Command the EVAP vent solenoid closed using a scan tool. Turn the nitrogen/smoke valve on the EEST control panel to SMOKE. Use the remote switch to introduce smoke into the EVAP system. Use the EVAP Service Port Vent Fitting (J 41413-VLV), or equivalent, to open the EVAP service port. Remove the EVAP service port vent fitting once smoke is observed. Continue to introduce smoke into the EVAP system for an additional 60 seconds. Check the entire EVAP system for exiting smoke using the High Intensity White Light (J 41413-SPT), or equivalent. Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step 6 . If no, go to next step.
5. Disconnect the fuel tank cap adapter from the fuel fill pipe. Install the fuel fill cap to the fuel fill pipe. Connect the EEST nitrogen/smoke supply hose to the EVAP service port. Use the remote switch to introduce smoke into the EVAP system. Check the entire EVAP system for exiting smoke using the high intensity light. Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
6. Perform the Service Bay Test. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to next step. If no, go to step 3 .
7. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

To aid in locating intermittent leaks, use the EVAP Pressure/Purge Diagnostic Station (J 41413) to pressurize the EVAP system. Move all EVAP components while testing using the Ultrasonic Leak Detector (J 41416).

1. To help locate intermittent leaks, use the Evaporative Emissions System Tester (EEST) (J 41413-200), or equivalent, to introduce smoke into the EVAP system. Move all EVAP components while observing smoke using the High Intensity White Light (J 41413-SPT), or equivalent.
2. To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles using the high intensity White light.
3. For intermittent conditions, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0443: EVAP PURGE SOLENOID CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

An ignition voltage is supplied directly to the Evaporative Emission (EVAP) canister purge valve. The EVAP canister purge valve is Pulse Width Modulated (PWM). The scan tool displays the amount of ON time as a percentage. The Powertrain Control Module (PCM) monitors the status of the driver. The PCM controls the EVAP canister purge valve ON time by grounding the control circuit via an internal switch called a driver. If the PCM detects an incorrect voltage for the commanded state of the driver, this DTC sets.

1. The engine speed is more than 400 RPM.
2. The system voltage is 6-18 volts.

1. The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
2. The above conditions are present for a minimum of 5 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - This step tests if the concern is active. The EVAP purge solenoid is Pulse Width Modulated (PWM). Clicking should be heard or felt when the purge solenoid is commanded to 50 percent and should stop when the EVAP purge solenoid is commanded to zero percent. The rate at which the valve cycles should increase as the commanded state is increased and decreased as the commanded state is decreased. Repeat the commands as necessary.
2. 5 - This step tests if a ground is constantly being applied to the EVAP purge solenoid.
3. 6 - This step verifies that the control module is providing ground to the EVAP purge solenoid.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine OFF. Command the EVAP purge solenoid to 50 percent and then to zero percent using a scan tool. Do you hear or feel a clicking from the EVAP purge solenoid when the solenoid is commanded to 50 percent? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Turn ignition switch to RUN position, engine OFF. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the EVAP purge solenoid harness connector. Turn ignition switch to RUN position, engine OFF. Probe the EVAP purge solenoid ignition 1 voltage circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 11 .
5. Connect a test light between the EVAP purge solenoid control circuit and the EVAP purge solenoid ignition 1 voltage circuit. Command the EVAP purge solenoid to zero percent using a scan tool. Does the test light illuminate? If yes, go to step 8 . If no, go to next step.
6. Command the EVAP purge solenoid to 50 percent using a scan tool. Does the test light illuminate or pulse when the EVAP purge solenoid is commanded to 50 percent? If yes, go to step 9 . If no, go to next step.
7. Test the EVAP purge solenoid control circuit for an open or short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
8. Test the EVAP purge solenoid control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
9. Test for an intermittent and for poor connection at the EVAP purge solenoid. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
10. Test for an intermittent and for a poor connection at the control module. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
11. Repair the open or short to ground in the EVAP purge solenoid ignition 1 voltage circuit. After repair, go to step 14 .
12. Replace the EVAP purge solenoid. After repair, go to step 14 .
13. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After repair, go to next step.
14. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0446: EVAP VENT SYSTEM PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

This DTC tests the Evaporative Emission (EVAP) system for a restricted or blocked EVAP vent path. The PCM commands the EVAP canister purge solenoid Open and the EVAP canister vent solenoid Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the PCM commands the EVAP canister purge solenoid Closed and the EVAP canister vent solenoid Open. The PCM monitors the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near zero in. H2O in a calibrated time, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP table.

EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0443, P0449, P0452, P0453, P1106, P1107, P1112, P1114, P1115, P1121 or P1122 are not set.
2. The ignition voltage is 10-18 volts.
3. The Barometric Pressure (BARO) sensor parameter is more than 75 kPa.
4. The Fuel Level sensor parameter is 15-80 percent.
5. The Engine Coolant Temperature (ECT) sensor parameter is 39-86°F (4-30°C).
6. The Intake Air Temperature (IAT) sensor parameter is 39-86°F (4-30°C).
7. The start-up ECT and IAT are within 16°F (9°C) of each other.
8. The Vehicle Speed Sensor (VSS) parameter is less than 75 MPH.

1. The Fuel Tank Pressure (FTP) sensor is less than -10 in. H2O.
2. The condition is present for as long as 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 4 - This test determines if the failure is present or intermittent.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Perform the Service Bay Test. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go to next step.
3. Check the EVAP system for the following conditions: A damaged EVAP vent solenoid. A pinched EVAP vent hose. A damaged EVAP canister. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
4. Turn ignition switch to OFF position. Disconnect the purge line from the EVAP purge solenoid. Turn ignition switch to RUN position, engine OFF. Is the Fuel Tank Pressure (FTP) sensor parameter -1 to 1 in. H2O? If yes, go to next step. If no, go to step 9 .
5. Turn ignition switch to OFF position. Connect the EVAP purge pipe. Connect the Evaporative Emissions System Tester (EEST) (J 41413-200), or equivalent, power supply clips to a known good 12-volt source. Install the Fuel Fill Cap Adapter (J 41415-40) to the fuel fill pipe. Connect the fuel fill cap to the fuel fill cap adapter. Connect the EEST nitrogen/smoke supply hose to the fuel fill cap adapter. Turn ignition switch to RUN position, engine OFF. Command the EVAP vent solenoid closed using a scan tool. Turn the nitrogen/smoke valve on the EEST control panel to NITROGEN. Use the remote switch to pressurize the EVAP system to 5 in. H2O. Observe the FTP sensor parameter using a scan tool. Command the EVAP vent solenoid open. Is the FTP Sensor parameter less than 1 in. H2O? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go to next step.
6. Disconnect the EVAP vent hose from the EVAP vent solenoid. Is the FTP sensor parameter less than 1 in. H2O? If yes, go to step 11 . If no, go to next step.
7. Disconnect the EVAP vent hose from the EVAP canister. Is the FTP sensor parameter less than 1 in. H2O? If yes, go to next step. If no, go to step 12 .
8. Repair the pinched or restricted EVAP vent hose. After repair, go to step 13 .
9. Test for an intermittent and for a poor connection at the Powertrain Control Module (PCM). Did you find and correct the condition? If yes, go to 13 . If no, go to next step.
10. Replace the FTP sensor. After repair, go to step 13 .
11. Replace the EVAP vent solenoid. After repair, go to step 13 .
12. Replace the EVAP canister. After repair, go to next step.
13. Perform the Service Bay Test. Go to «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to next step. If no, go to step 3 .
14. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent solenoid inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.
2. For intermittent conditions, refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0449: EVAP VENT SOLENOID CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

An ignition voltage is supplied to the Evaporative Emission (EVAP) canister vent valve. The Powertrain Control Module (PCM) grounds the EVAP canister vent valve control circuit to close the valve by means of an internal switch called a driver. The scan tool displays the commanded state of the EVAP canister vent valve as ON or OFF. The PCM monitors the status of the driver. If the PCM detects an incorrect voltage for the commanded state of the driver, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister vent valve. See PCM TO EVAP CANISTER VENT VALVE RELATIONSHIP table.

PCM TO EVAP CANISTER VENT VALVE RELATIONSHIP

1. The engine speed is more than 400 RPM.
2. The system voltage is 6-18 volts.

1. The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
2. The above conditions are present for a minimum of 5 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - Listen or feel for a click when the EVAP vent solenoid operates. Ensure that both the ON and the OFF states are commanded. Repeat the commands as necessary.
2. 5 - This step verifies that the PCM is providing ground to the EVAP vent solenoid.
3. 6 - This step tests if the EVAP vent solenoid control circuit is grounded.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine OFF. Command the EVAP vent solenoid ON and OFF using the scan tool. Do you hear or feel a click from the EVAP vent solenoid when commanded ON and OFF? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Turn ignition switch to RUN position, engine OFF. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the EVAP vent solenoid. Turn ignition switch to RUN position, engine OFF. Probe the EVAP vent solenoid ignition 1 voltage circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 11 .
5. Connect a test light between the control circuit of the EVAP vent solenoid and the ignition 1 voltage circuit of the EVAP vent solenoid. Command the EVAP vent valve ON and OFF using a scan tool. Does the test light turn ON or OFF with each command? If yes, go to step 9 . If no, go to next step.
6. Does the test light remain illuminated with each command? If yes, go to step 8 . If no, go to next step.
7. Test the control circuit for an open or short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
8. Test the control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the EVAP vent solenoid. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
10. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
11. Repair the open or short to ground in the ignition 1 voltage circuit. Replace the fuse if necessary. After repair, go to step 14 .
12. Replace the EVAP vent solenoid. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0452: FUEL TANK PRESSURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Fuel Tank Pressure (FTP) sensor measures the difference between the air pressure or vacuum in the Evaporative Emission (EVAP) system, and the outside air pressure. The PCM supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage goes below a calibrated value, this DTC sets.

The following table illustrates the relationship between the FTP sensor signal voltage and the EVAP system pressure/vacuum. See FTP SENSOR SIGNAL VOLTAGE & EVAP SYSTEM PRESSURE/VACUUM RELATIONSHIP table.

FTP SENSOR SIGNAL VOLTAGE & EVAP SYSTEM PRESSURE/VACUUM RELATIONSHIP

The ignition switch is in RUN position.

1. The FTP sensor voltage is less than 0.1 volt.
2. All conditions are present for more than 5 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The Malfunction Indicator Light (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Using scan tool, clear DTCs.

The number below refers to the step number in the diagnostic procedure.

1. 5 - This step tests for the proper operation of the circuit in the high voltage range.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Idle the engine for one minute. Monitor the Diagnostic Trouble Codes (DTC) information using the scan tool. Did DTC P1635 or P1639 fail this ignition? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
3. Observe the Fuel Tank Pressure (FTP) sensor voltage using a scan tool. Is the FTP sensor parameter less than 0.1 volt? If yes, go to step 5 . If no, go to next step.
4. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. Go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Turn ignition switch to OFF position. Disconnect FTP sensor harness connector. Connect a 3-amp fused jumper wire between the FTP sensor 5-volt reference circuit and the FTP sensor signal circuit. Turn ignition switch to RUN position, engine OFF. Observe the FTP sensor using a scan tool. Is the FTP sensor parameter 4.8-5.2 volts? If yes, go to step 8 . If no, go to next step.
6. Test the FTP 5-volt reference circuit for a short to ground, for high resistance, or for an open. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
7. Test the FTP signal circuit for a short to ground, for high resistance, or for an open. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 9 .
8. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace the FTP sensor. After repair, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0453: FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Fuel Tank Pressure (FTP) sensor measures the difference between the air pressure or vacuum in the Evaporative Emission (EVAP) system, and the outside air pressure. The PCM supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage increases above a calibrated value, this DTC sets.

The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum. See FTP SENSOR SIGNAL VOLTAGE & EVAP SYSTEM PRESSURE/VACUUM RELATIONSHIP table.

The ignition switch is in RUN position.

The FTP sensor voltage is more than 4.9 volts for more than 5 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The Malfunction Indicator Light (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Using scan tool, clear DTCs.

The number below refers to the step number in the diagnostic procedure.

1. 2 - If DTC P1639 set, the 5-volt reference circuit may be shorted to a voltage.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Idle the engine for one minute. Monitor the Diagnostic Trouble Code (DTC) Information using the scan tool. Did DTC P1635 or P1639 fail this ignition? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, go to next step.
3. Turn ignition switch to RUN position, engine OFF. Observe the Fuel Tank Pressure (FTP) sensor parameter using a scan tool. Is the FTP sensor parameter more than 4.3 volts? If yes, go to step 5 . If no, go to next step.
4. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Turn ignition switch to OFF position. Disconnect the FTP sensor harness connector. Turn ignition switch to RUN position, engine OFF. Observe the FTP sensor parameter using a scan tool. Is the FTP sensor parameter more than 4.3 volts? If yes, go to next step. If no, go to step 7 .
6. Test the FTP signal circuit for a short to voltage or a short to a 5-volt reference circuit. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
7. Probe the FTP sensor low reference circuit using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 9 . If no, go to next step.
8. Test the FTP sensor low reference circuit for an open. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
9. Check for poor connections at the FTP sensor harness connector. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 11 .
10. Check for poor connections at the PCM harness connectors. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
11. Replace FTP sensor. After repair, go to step 13 .
12. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
13. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
14. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0506: IDLE SPEED LOW

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is supplied current by two circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts using a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed Diagnostic Trouble Code (DTC) sets.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0401, P0403, P0404, P0405 or P0502 are not set.
2. The Engine Run Time parameter is more than 2 minutes.
3. The Engine Coolant Temperature (ECT) sensor parameter is more than 158°F (70°C).
4. The Idle Air Temperature (IAT) sensor parameter is more than -0.4°F (-18°C).
5. The Barometric Pressure (BARO) sensor parameter sensor parameter is more than 70 kPa.
6. The Ignition 1 Signal parameter is 9-18 volts.
7. The Throttle Position (TP) sensor parameter is less than 1.5 percent.
8. The Vehicle Speed Sensor (VSS) parameter is less than 3 MPH.
9. The above conditions are met for more than 8 seconds.

1. The Engine Speed parameter is 100 RPM less than the Desired Idle Speed parameter for more than 8 seconds for each test.
2. The PCM detects the IAC test failed 4 consecutive times in one ignition cycle.
3. The vehicle must enter the above criteria and then leave the criteria for one second to complete one IAC test.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - This test will determine the ability of the PCM and IAC valve control circuits to control the IAC valve.
2. 7 - This test will determine the ability of the PCM to provide the IAC valve control circuits with a ground. On a normal operating system, the test light should not flash while the IAC Counts are incrementing.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Set parking brake and block drive wheels. Start the engine. Turn all accessories OFF. Use scan tool RPM CONTROL function to slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit RPM CONTROL function. Does engine speed stabilized within 100 RPM of the commanded RPM? If yes, go to next step. If no, go to step 4 .
3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within code enable criteria or as close to FREEZE FRAME/FAILURE RECORDS data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Turn ignition switch to OFF position. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J 37027-A), or equivalent, to the IAC valve. Start the engine. Use IAC motor driver to command IAC valve in until 600 RPM is reached. Use IAC motor driver to command IAC valve out until 1700 RPM is reached. Return engine speed to desired idle as indicated on scan tool data list. Did the engine speed parameter steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the IAC valve was commanded in and out? If yes, go to next step. If no, go to step 11 .
5. Connect a test light between one of the IAC valve control circuits and a good ground. Start the engine. Observe the IAC Counts parameter using a scan tool. Command high RPM with the IAC Motor Driver until the IAC Counts parameter starts to increment. Command low RPM with the IAC Motor Driver until the IAC Counts parameter starts to increment. Return the Engine Speed parameter to the Desired Idle Speed parameter. Repeat the above procedure for the other three IAC valve control circuits. Did the test light remain illuminated, never flashing, while the IAC Counts were incrementing for any of the IAC valve control circuits? If yes, go to step 10 . If no, go to next step.
6. Did the test light remain OFF, never flashing, while the IAC counts where incrementing at any of the IAC valve control circuits during the test? If yes, go to step 9 . If no, go to next step.
7. Connect a test light between the IAC coil "A" low circuit and the IAC coil "A" high circuit. Observe the IAC Counts parameter using a scan tool and observe the test light. Command high RPM using the IAC Motor Driver until the IAC Counts parameter starts to increment. Command low RPM using the IAC Motor Driver until the IAC Counts parameter starts to increment. Return the Engine Speed parameter to the Desired Idle Speed parameter. Repeat the above procedure using the test light connected between the IAC coil "B" low control circuit and the IAC coil "B" high control circuit. Did the test light stay illuminated and never flashing while the IAC Counts were incrementing for any of the IAC valve control circuits? If yes, go to next step. If no, go to step 16 .
8. Check for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 12 .
9. Turn ignition switch to OFF position. Disconnect PCM harness connectors. Using a DMM, test the circuit where test light remained OFF for an open circuit, short to ground, or short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 12 .
10. Turn ignition switch to RUN position, engine off. Using a DMM, test the circuit where the test light remained ON for the following: A short to voltage, or short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 12 .
11. Visually/Physically inspect for the following: Throttle body damage and tampering. Throttle lever screw tampering (if equipped). Restricted air intake system. Check for a possible collapsed or clogged air intake duct before and after air filter element, restricted air filter element, or restriction at throttle body intake screen, if equipped. Remove IAC valve. Check for the following: A clogged IAC passage. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Excessive deposits on IAC valve pintle. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 14 .
12. Check for a poor connection at the PCM harness connectors. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
13. Disconnect PCM harness connectors. Using a DMM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 16 .
14. Check for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
15. Replace IAC valve. When complete, go to step 17 .
16. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
17. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
18. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

Check for the following conditions

1. A high resistance in an IAC control circuit.
2. A restricted air intake system.
3. Proper operation and installation of all air intake components.
4. Any collapsed, clogged, or loose air intake ducts.
5. A clogged air filter.
6. Proper operation of the Mass Airflow (MAF) sensor, if equipped.
7. A tampered with or damaged throttle stop screw.
8. A tampered with or damaged throttle plate, throttle shaft, or throttle linkage.
9. Objects blocking the IAC passage or throttle bore.
10. Excessive deposits in the IAC passage or on the IAC pintle.
11. Excessive deposits in the throttle bore or on the throttle plate.
12. Vacuum leaks.
13. A low or unstable idle condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve.
14. If the problem is determined to be intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0507: IDLE SPEED HIGH

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is supplied current by two circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts using a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed Diagnostic Trouble Code (DTC) sets.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0401, P0403, P0404, P0405 or P0502 are not set.
2. The Engine Run Time parameter is more than 2 minutes.
3. The Engine Coolant Temperature (ECT) sensor parameter is more than 158°F (70°C).
4. The Idle Air Temperature (IAT) sensor parameter is more than -0.4°F (-18°C).
5. The Barometric Pressure (BARO) sensor parameter sensor parameter is more than 70 kPa.
6. The Ignition 1 Signal parameter is 9-18 volts.
7. The Throttle Position (TP) sensor parameter is less than 1.5 percent.
8. The Vehicle Speed Sensor (VSS) parameter is less than 3 MPH.
9. The above conditions are met for more than 8 seconds.

1. The Engine Speed parameter is 150 RPM more than the Desired Idle Speed parameter for more than 8 seconds for each test.
2. The PCM detects the IAC test failed 4 consecutive times in one ignition cycle.
3. The vehicle must enter the above criteria and then leave the criteria for one second to complete one IAC test.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - This test will determine the ability of the PCM and IAC valve circuits to control the IAC valve.
2. 7 - This test will determine the ability of the PCM to provide the IAC valve circuits with a ground. On a normally operating system, the test light should not flash while the IAC counts are incrementing.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Set parking brake and block drive wheels. Install scan tool. Start the engine. Turn off all accessories. Use scan tool RPM CONTROL function to slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit RPM CONTROL function. Does the engine speed stabilize within 200 RPM of the commanded RPM during the test? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test, and within the parameters observed in the freeze Frame/Failure Records. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC fail this ignition? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Turn ignition switch to OFF position. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J 37027-A) to IAC valve. Start the engine. Use IAC motor driver to command IAC valve in until 600 RPM is reached. Use IAC motor driver to command IAC valve out until 1700 RPM is reached. Return engine to desired idle speed as indicated on scan tool data list. Did the engine speed steadily decrease to about 600 RPM and steadily increase to about 1700 RPM when the IAC valve was commanded in and out? If yes, go to next step. If no, go to step 11 .
5. Connect the test light between one of the IAC valve control circuits and a good ground. Start the engine. Observe the IAC Counts parameter using a scan tool and observe the test light. Command high RPM using the IAC Motor Driver until the IAC counts parameter starts to increment. Command low RPM using the IAC Motor Driver until the IAC Counts parameter starts to increment. Return the engine speed parameter to the desired idle speed parameter. Repeat the above procedure for the other three IAC valve control circuits. Did the test light remain ON, never flashing, while the IAC Counts were incrementing for any of the IAC valve control circuits? If yes, go to step 10 . If no, go to next step.
6. Did test light remained off (never flashing) while IAC counts were incrementing at any of IAC valve circuits during the test? If yes, go to step 9 . If no, go to next step.
7. Connect a test light between the IAC coil "A" low control circuit and the IAC coil "A" high control circuit. Observe the IAC counts parameter using a scan tool and observe the test light. Command high RPM using the AC Motor Driver until the IAC counts parameter starts to the increment. Command low RPM using the AC Motor Driver until the IAC Counts parameter starts to increment. Return the Engine Speed parameter to the Desired Idle Speed parameter as indicated on the scan tool data list. Repeat the above procedure using the test light connected between the IAC coil "B" low control circuit and the IAC coil "B" high control circuit. Did the test light stay illuminated and never flashing while the IAC Counts were incrementing for any of the IAC valve control circuits? If yes, go to next step. If no, go to step 16 .
8. Check for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 12 .
9. Turn ignition switch to OFF position. Disconnect PCM harness connectors. Using a DMM, test the circuit where test light remained OFF for an open circuit, short to ground or short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 12 .
10. Turn ignition switch to RUN position, engine off. Using a DMM, test the circuit where the test light remained ON for a short to voltage or short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 12 .
11. Visually/Physically inspect for the following: Throttle body damage and tampering. Throttle lever screw tampering (if equipped). Vacuum leaks. Faulty, incorrectly installed PCV valve and hose (if equipped). Throttle shaft binding. Throttle linkage or cruise control linkage binding (if equipped). Remove IAC valve. Check for the following: Debris in the IAC passage. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Excessive deposits on IAC valve pintle. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 14 .
12. Check for an intermittent and a poor connection at the PCM harness connectors. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
13. Disconnect PCM harness connectors. Check all IAC valve control circuits for high resistance. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 16 .
14. Check for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
15. Replace IAC valve. After repair, go to step 17 .
16. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
17. Using scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
18. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

Check for the following conditions

1. A high resistance in an IAC control circuit.
2. A restricted air intake system.
3. Proper operation and installation of all air intake components.
4. Any collapsed, clogged, or loose air intake ducts.
5. A clogged air filter.
6. Proper operation of the Mass Airflow (MAF) sensor, if equipped.
7. A tampered with or damaged throttle stop screw.
8. A tampered with or damaged throttle plate, throttle shaft, or throttle linkage.
9. Objects blocking the IAC passage or throttle bore.
10. Excessive deposits in the IAC passage or on the IAC pintle.
11. Excessive deposits in the throttle bore or on the throttle plate.
12. Vacuum leaks.
13. A low or unstable idle condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve.
14. If the problem is determined to be intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683 OR P2610: ECU MALFUNCTION

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Note. DTC P0601, P0602 or P1621 may not be applicable to all vehicles.

This diagnostic applies to internal microprocessor integrity conditions within the Powertrain Control Module (PCM). This diagnostic also addresses if the PCM is not programmed.

The number below refers to the step number in the diagnostic procedure.

1. 2 - A DTC P0602 indicates the PCM is not programmed.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0602 set? If yes, go to next step. If no, go to step 5 .
3. Program PCM. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. Does DTC P0602 reset? If yes, go to next step. If no, go to step 6 .
4. Ensure all tool connections are secure. Ensure programming equipment is operating correctly. Ensure correct software/calibration package is used. Attempt to program PCM. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. Does DTC P0602 reset? If yes, go to next step. If no, go to step 6 .
5. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
6. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
7. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P0650: MIL CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Malfunction Indicator light (MIL) is located on the Instrument Panel Cluster (IPC). The MIL informs the driver that an emission system fault has occurred and that the engine control system requires service. The Powertrain Control Module (PCM) monitors the MIL control circuit for conditions that are incorrect for the commanded state of the MIL. For example, a failure condition exists if the PCM detects low voltage when the MIL is commanded OFF, or high voltage when the MIL is commanded ON. If the PCM detects an improper voltage on the MIL control circuit, DTC P0650 will set.

The ignition switch is in RUN position.

1. The PCM detects that the commanded state of the MIL driver and the actual state of the control circuit do not match.
2. The conditions are present for a minimum of 30 seconds.

1. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 - This step tests for a short to ground in the MIL control circuit. With the Powertrain Control Module (PCM) disconnected and the ignition ON, the MIL should be OFF.
2. 6 - This step tests for a short to voltage on the MIL control circuit. With the fuse removed, there should be no voltage on the MIL control circuit.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Verify whether the instrument cluster is operational. If the Instrument Panel (IP) is completely inoperative, go to Instrument Cluster Diagnostic System Check in appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Command the MIL ON and OFF using a scan tool. Does the MIL turn ON and OFF when commanded using a scan tool? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Check the fuse that supplies battery voltage to the MIL. Is the fuse open? If yes, go to step 12 . If no, go to next step.
5. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position. Is the MIL OFF? If yes, go to next step. If no, go to step 13 .
6. Turn ignition switch to OFF position. Remove the fuse that supplies voltage to the MIL. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the MIL control circuit in the PCM to a good ground. Is the voltage less than 0.3 volt? If yes, go to next step. If no, go to step 14 .
7. Turn ignition switch to OFF position. Install the fuse that supplies voltage to the MIL. Turn ignition switch to RUN position, engine OFF. Connect a 3-amp fused jumper wire between the MIL control circuit of the PCM and a good ground. Is the MIL illuminated? If yes, go to step 11 . If no, go to next step.
8. Turn ignition switch to OFF position. Remove the Instrument Panel Cluster (IPC). Probe the MIL battery positive voltage circuit of the IPC harness connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 15 .
9. Test the MIL control circuit for an open or high resistance. Did you find and correct a condition? If yes, go to step 18 . If no, go to next step.
10. Test for an intermittent and for a poor connection at the IPC. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
11. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
12. Repair the short to ground in the battery positive voltage circuit. After repair, go to step 18 .
13. Repair the short to ground in the MIL control circuit. After repair, go to step 18 .
14. Repair the short to voltage in the MIL control circuit. After repair, go to step 18 .
15. Repair the open in the MIL battery positive voltage. After repair, go to step 18 .
16. Replace the IPC. After repair, go to step 18 .
17. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
18. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
19. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1106: MAP SENSOR CIRCUIT INTERMITTENT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition switch is in RUN position, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned to RUN position, engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is intermittently high, DTC P1106 sets.

1. DTCs P0121, P0122 or P0123 are not set.
2. The engine has been running for a period of time that is determined by the start-up coolant temperature. The time ranges from 2 minutes at less than -22°F (-30°C) to one second at more than 86°F (30°C).
3. The throttle angle is less than 2 percent when the engine speed is less than 3000 RPM or the throttle angle is less than 30 percent when the engine speed is more than 3000 RPM.

The PCM detects that the MAP sensor voltage is intermittently more than 4.2 volts.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number on the diagnostic procedure.

1. 3 - Many intermittent open or shorted circuits occur with harness/connector movement caused by vibration, by engine torque, and by bumps. This step attempts to recreate this condition.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Monitor the Diagnostic Trouble Code (DTC) information using the scan tool. Does the scan tool display DTC P1635 or P0108 set? If yes, go to appropriate DTC. If no, go to next step.
3. Observe the MAP sensor parameter using the scan tool. Attempt to induce the fault that set the DTC by manipulating the following items: The MAP sensor wiring harness. The MAP sensor connector. The PCM connector. Is the MAP sensor voltage affected during any part of the test? If yes, go to next step. If no, go to step 8 .
4. Test the low reference circuit between the PCM and the MAP sensor for an intermittent open or a high resistance. Did you find and correct the condition? If yes, go to next step. If no, go to step 8 .
5. Test the MAP sensor signal circuit between the PCM and the MAP sensor for an intermittent short to voltage. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
6. Test for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
7. Test for an intermittent and for a poor connection at the PCM. Repair as necessary. After repair, go to next step.
8. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
9. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1107: MAP SENSOR CIRCUIT INTERMITTENT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition switch is in RUN position, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned to RUN position, engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is intermittently high, DTC P1106 sets.

1. DTCs P0121, P0122 or P0123 are not set.
2. The ignition switch is in RUN position.
3. The throttle angle is more than zero percent when the engine speed is less than 1000 RPM or the throttle angle is more than 10 percent when the engine speed is more than 1000 RPM.

The PCM detects that the MAP sensor voltage is intermittently less than 0.1 volt.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number on the diagnostic procedure.

1. 3 - Many intermittent open or shorted circuits come and go with harness/connector movement caused by vibration, by engine torque, and by bumps. This step attempts to recreate this condition.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Monitor the Diagnostic Trouble Code (DTC) information using the scan tool. Does the scan tool display DTC P1107 or P1635? If yes, go to appropriate DTC. If no, go to next step.
3. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor parameter using the scan tool. Attempt to induce the fault that set the DTC by manipulating the following items: The MAP sensor wiring harness. The MAP sensor connector. The PCM connector. Is the MAP sensor voltage affected during any part of the test? If yes, go to next step. If no go to step 8 .
4. Test the 5-volt reference circuit between the PCM and the MAP sensor for an intermittent open or a high resistance. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
5. Test the MAP sensor signal circuit between the PCM and the MAP sensor for the following conditions: A short to ground. An open. High resistance. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
6. Test for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
7. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? After repair, go to next step.
8. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
9. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1111: IAT SENSOR CIRCUIT INTERMITTENT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an intermittent high IAT signal voltage, indicating a low temperature, DTC P1111 sets.

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0502 or P0503 are not set.
2. The Vehicle Speed Sensor (VSS) is less than 35 MPH.
3. The Mass Airflow (MAF) is less than 12 g/s.
4. The Engine Coolant Temperature (ECT) sensor parameter is more than 140°F (60°C).
5. The engine run time is more than 180 seconds.

The PCM detects that the Intake Air Temperature (IAT) sensor parameter is less than -36°F (-38°C) intermittently for more than 3 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the DTC Information using a scan tool. Is DTC P0113 set? If yes, go to «DTC P0113: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0113-intake-air-temperature-sensor) . If no, go to next step.
3. Test for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
4. Test the IAT signal circuit between the IAT sensor and the PCM for an intermittent open. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
5. Test the IAT signal circuit between the IAT sensor and the PCM for an intermittent short to voltage. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
6. Test the low reference circuit for an intermittent open. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
7. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
8. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
9. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1112: IAT SENSOR CIRCUIT INTERMITTENT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an intermittent low IAT signal voltage, indicating a high temperature, DTC P1112 sets.

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0502 or P0503 are not set.
2. The engine run time is more than 10 seconds.
3. The Vehicle Speed Sensor (VSS) indicates that vehicle speed is more than 25 MPH.

The PCM detects that the Intake Air Temperature (IAT) sensor parameter is more than 253°F (123°C) intermittently for more than 20 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the DTC information using a scan tool. Is DTC P0112 set? If yes, go to step «DTC P0112: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0112-intake-air-temperature-sensor) .
3. Test for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step 5 . If no, go to next step.
4. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
5. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
6. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1114: ECT SENSOR CIRCUIT INTERMITTENT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P1114 sets.

The engine run time is more than 5 seconds.

The PCM detects that the ECT sensor parameter is more than 282°F (139°C) intermittently for more than 5 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the DTC information using a scan tool. Is DTC P0117 set? If yes, go to «DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0117-engine-coolant-temperature-sensor) . If no, go to next step.
3. Observe the Engine Coolant Temperature (ECT) parameter using a scan tool while moving the ECT sensor connector and the Powertrain Control Module (PCM) connector. Does the scan tool indicate an abrupt change in value? If yes, go to step 5 . If no, go to next step.
4. Observe the ECT parameter using a scan tool while moving the wiring harness at the ECT sensor and the PCM. Does the scan tool indicate an abrupt change in value? If yes, go to step 6 . If no, go to step 7 .
5. Repair the connector/terminal as necessary. After repair, go to step 7 .
6. Repair the harness/wiring as necessary. After repair, go to next step.
7. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
8. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1115: ECT SENSOR CIRCUIT INTERMITTENT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high signal voltage, which is a low temperature indication, DTC P1115 sets.

The engine run time is more than 5 seconds.

The PCM detects that the ECT sensor parameter is less than -36°F (-38°C) intermittently for more than 5 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the DTC information using a scan tool. Is DTC P0118 set? If yes, go to «DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0118-engine-coolant-temperature-sensor) . If no, go to next step.
3. Observe the Engine Coolant Temperature (ECT) parameter using a scan tool while moving the ECT sensor connector and the Powertrain Control Module (PCM) connector. Does the scan tool indicate an abrupt change in value? If yes, go to step 5 . If no, go to next step.
4. Observe the ECT parameter using a scan tool while moving the wiring harness at the ECT sensor and the PCM. Does the scan tool indicate an abrupt change in value? If yes, go to step 6 . If no, go to step 7 .
5. Repair the connector/terminal as necessary. After repair, go to step 7 .
6. Repair the harness/wiring as necessary. After repair, go to next step.
7. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
8. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1121: TP SENSOR CIRCUIT - INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with three circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A TP sensor signal circuit.

The PCM provides the TP sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from below 1.0 volt to greater than 4.0 volts through the TP sensor signal circuit. If the PCM detects an intermittent excessively high signal voltage, DTC P1121 sets.

The ignition switch is in RUN position.

The PCM detects that the TP sensor voltage is intermittently more than 4.9 volts.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the DTC using a scan tool.

The number below refers to the step number in the diagnostic procedure.

1. 7 - This test will determine an intermittent faulty TP sensor utilizing the DMMs MIN MAX, 100 millisecond capture mode.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to OFF position. Disconnect the Throttle Position (TP) sensor harness connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the TP sensor 5-volt reference circuit to a good ground using a DMM. Lightly touch and move the related engine wiring harnesses and connectors for all 5-volt reference circuits while observing voltage. Any change in voltage indicates the area where a short to voltage may be found. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
3. Measure the voltage from the TP sensor signal circuit to a good ground using a DMM. Lightly touch and move the related engine wiring harnesses and connectors while observing voltage. Any change in voltage indicates the area where a short to voltage may be found. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
4. Measure the resistance from the TP sensor low reference circuit to a good ground using a DMM. Lightly touch and move the related engine wiring harnesses and connectors while observing resistance. Any change in resistance indicates the area where an open or high resistance may be found. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
5. Test for poor connections at the TP sensor harness connector. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
6. Test for poor connections at the Powertrain Control Module (PCM) harness connector. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
7. Turn ignition switch to OFF position. Measure the resistance between the TP sensor signal terminal and the TP sensor low reference terminal using the MIN MAX function on the DMM. Slowly depress the accelerator pedal to the Wide Open Throttle (WOT) position, then release the pedal back to the closed throttle position several times. Did you observe a MAX value of infinite ohms or a MIN value of zero ohms? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
8. Replace the TP sensor. After repair, go to next step.
9. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
10. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1122: TP SENSOR CIRCUIT INTERMITTENT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with three circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A TP sensor signal circuit.

The PCM provides the TP sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from below 1.0 volt to greater than 4.0 volts through the TP sensor signal circuit. If the PCM detects an intermittent excessively high signal voltage, DTC P1121 sets.

The ignition switch is in RUN position.

The PCM detects that the TP sensor voltage is intermittently less than 0.1 volt.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
3. Clear the DTC using a scan tool.

The number below refers to the step number on the diagnostic procedure.

1. 6 - This test will determine an intermittent faulty TP sensor utilizing the DMMs MIN MAX, 100 millisecond capture mode.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to OFF position. Disconnect the Throttle Position (TP) sensor harness connector. Probe the TP sensor 5-volt reference circuit using a test light connected to a good ground. Turn ignition switch to RUN position, engine off. Lightly touch and move the related engine wiring harnesses and connectors for all 5-volt reference circuits while observing the test light. Any change in illumination indicates the area where an open, a high resistance or a short to ground in the 5-volt reference circuit may be found. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
3. Connect the TP sensor. Install a scan tool and observe the TP sensor voltage parameter. Lightly touch and move the related engine wiring harnesses and connectors for the TP sensor signal circuit while observing voltage. Any change in voltage indicates the area where an open, a high resistance, or a short to ground in the TP sensor signal circuit may be found. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
4. Test for poor connections at the TP sensor harness connector. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
5. Test for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Measure the resistance between the TP sensor signal terminal and the 5-volt reference terminal at the TP sensor using the MIN MAX function on the DMM. Slowly depress the accelerator pedal to the Wide Open Throttle (WOT) position, then release the pedal back to the closed throttle position several times. Did you observe a MAX value of infinite ohms or a MIN value of zero ohms? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
7. Replace the TP sensor. After repair, go to next step.
8. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
9. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1133: HO2S 1 - INSUFFICIENT SWITCHING

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If the PCM detects that the HO2S 1 voltage did not switch enough times during a calibrated time period, DTC P1133 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The vehicle is not in Park or Neutral.
3. The Engine Run Time parameter is at least 60 seconds.
4. The Loop Status parameter is closed.
5. The MAF sensor parameter is 13-30 g/s.
6. The Engine Speed parameter is 1300-3000 RPM.
7. The ECT Sensor parameter is more than 158°F (70°C).
8. The system voltage is 9-18 volts.

The PCM detects that the HO2S 1 voltage switched from rich-to-lean fewer than 20 times within a 100 monitoring period or the PCM detects that the HO2S 1 voltage switched from lean-to-rich fewer than 20 times within a 100 monitoring period.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 4 - A voltage reading other than the specified amount in this step indicates an open circuit condition in the high signal circuit or the PCM.
3. 6 - This step tests the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
4. 8 - This step tests for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control is controlled by the PCM. The engine must be running to enable the HO2S heater.
5. 9 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Operate engine at normal operating temperature. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Does the HO2S 1 voltage fluctuate rapidly above and below 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. Go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect HO2S 1 harness connector. Turn ignition switch to RUN position, engine off. Measure the voltage between the HO2S 1 high signal circuit on the PCM side to a good ground. Is the HO2S 1 voltage 0.425-0.500 volt? If yes, go to next step. If no, go to step 6 .
5. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit and HO2S 1 low signal circuit. Turn ignition switch to RUN position, engine off. Observe the HO2S 1 voltage using a scan tool. Is the HO2S 1 voltage less than 25 mV? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Disconnect both PCM connectors. Measure the resistance of each of the following circuits with a DMM: HO2S 1 high signal circuit between HO2S connector and the PCM connector. HO2S 1 low reference circuit between HO2S connector and the PCM connector. Low reference loop between PCM harness connector C1 terminal No. 29 and PCM harness connector C2 terminal No. 80. Is the resistance of each circuit less than 5 ohms? If yes, go to step 11 . If no, go to next step.
7. Repair the circuit that measured a high resistance or an open. After repair, go to step 14 .
8. Remove the jumpers from the HO2S 1 terminals. Connect a test light between the HO2S heater ignition voltage circuit, and HO2S heater low control circuit terminals, on the engine harness side. Start the engine. Does the test light illuminate? If yes, go to next step. If no, go to «DTC P0135: HO2S 1 HEATER PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0135-ho2s-1-heater-performance) .
9. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. See «INSPECTION/MAINTENANCE EVAPORATIVE EMISSION SYSTEM SET PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
10. Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace HO2S 1. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1134: HO2S 1 TRANSITION TIME RATIO

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The PCM calculates a transition time ratio for rich-to-lean and lean-to-rich HO2S voltage switches. If the PCM detects that the calculated transition time ratio is incorrect, DTC P1134 will set.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

1. DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
2. The vehicle is not in Park or Neutral.
3. The Engine Run Time parameter is at least 60 seconds.
4. The Loop Status parameter is closed.
5. The MAF sensor parameter is 13-30 g/s.
6. The Engine Speed parameter is 1300-3000 RPM.
7. The ECT Sensor parameter is more than 158°F (70°C).
8. The system voltage is 9-18 volts.

The PCM detects that the average transition time ratio is not within 0.4-4.2 during a 100 second monitoring period.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 - A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
2. 4 - A voltage reading other than the specified amount in this step indicates an open circuit condition in the high signal circuit or the PCM.
3. 6 - This step tests the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
4. 8 - This step tests for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control is controlled by the PCM. The engine must be running to enable the HO2S heater.
5. 9 - The conditions listed in the test may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 1 voltage parameter using a scan tool. Does the HO2S 1 voltage fluctuate rapidly above and below 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. Go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
4. Turn ignition switch to OFF position. Disconnect the HO2S 1 harness connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the high signal circuit of the HO2S 1 harness connector on the engine harness side to a good ground using a DMM. Is the HO2S 1 voltage 0.425-0.500 volt? If yes, go to next step. If no, go to step 6 .
5. Turn ignition switch to OFF position. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit and the HO2S 1 low reference signal circuit. Turn ignition switch to RUN position, engine off. Observe the HO2S 1 voltage using a scan tool. Is the HO2S 1 voltage less than 25 mV? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Disconnect both PCM harness connectors. Measure the resistance of each of the following circuits using a DMM: HO2S 1 high signal circuit between HO2S 1 harness connector and the PCM harness connector. HO2S 1 low reference circuit between HO2S 1 harness connector and the PCM harness connector. Low reference loop between PCM harness connector C1 terminal No. 29 and PCM harness connector C2 terminal No. 80. Is the resistance of each circuit less than 5 ohms? If yes, go to step 11 . If no, go to next step.
7. Repair the circuit that measured a high resistance or an open. After repair, go to step 14 .
8. Remove the jumpers from the HO2S 1 terminals. Connect a test light between the HO2S heater ignition voltage circuit, and HO2S heater low control circuit terminals on the engine harness side. Start the engine. Does the test light illuminate? If yes, go to next step. If no, go to «DTC P0135: HO2S 1 HEATER PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0135-ho2s-1-heater-performance) .
9. Check for the following that may affect the HO2S operation: HO2S for contamination. Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring. The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions. Exhaust system leaks or restrictions. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Evaporative Emissions (EVAP) system malfunction. See «INSPECTION/MAINTENANCE EVAPORATIVE EMISSION SYSTEM SET PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
10. Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace the HO2S 1 sensor. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1336: CRANKSHAFT POSITION SYSTEM VARIATION NOT LEARNED

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Crankshaft Position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft and the CKP sensors. The calculated error allows the Powertrain Control Module (PCM) to accurately compensate for reference period variations. This enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load.

The PCM stores the CKP system variation values after a learn procedure has been performed. If the CKP system variation values are not stored in the PCM memory, DTC P1336 sets.

1. DTCs P0336, P0341 or P1374 are not set.
2. The Engine Coolant Temperature (ECT) sensor parameter is more than 158°F (70°C).

The CKP system variation values are not stored in the PCM memory.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Perform the CKP system variation learn procedure. Is the action complete? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
4. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

The CKP system variation compensating values are stored in PCM memory after a learn procedure has been performed. If the actual CKP variation is not within the CKP system variation compensating values stored in the PCM, DTC P0300 may set.

The CKP system variation learn procedure is also required when the following service procedures have been performed, regardless of whether DTC P1336 is set.

1. Engine replacement.
2. PCM replacement.
3. A harmonic balancer replacement.
4. Crankshaft replacement.
5. CKP sensor replacement.
6. Any engine repairs which disturb the crankshaft to CKP sensor relationship.

If the CKP system variation learn procedure cannot be performed successfully, inspect for the following conditions and correct as necessary

1. A damaged reluctor wheel.
2. Excessive crankshaft runout.
3. A damaged crankshaft.
4. Interference in the signal circuit of the CKP sensor.
5. A coolant temperature not within the Condition For Running the DTC.
6. The ignition switch is in the RUN position until the battery is drained.
7. A PCM power disconnect with the ignition switch in the RUN position may erase the stored value and set the DTC P1336.

DTC P1351: IGNITION COIL CONTROL CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Ignition Control Module (ICM) has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consists of the following circuits

1. The Ignition Control (IC) timing signal.
2. The IC timing control.
3. The low resolution engine speed signal.
4. The low reference signal.

The ICM sends 3X signals to the PCM and controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions occur

1. The PCM receives the second 3X signal.
2. The PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

If the PCM detects an open in the IC timing control circuit, DTC P1351 sets.

The engine speed is greater than 600 RPM.

1. The PCM detects an open in the IC timing control circuit.
2. The condition is present for 300 3X reference periods, 100 crankshaft revolutions.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. Go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position, engine OFF. Measure the resistance from the Ignition Control (IC) timing control circuit of the Ignition Control Module (ICM) to the low reference circuit of the ICM using a DMM. Is the resistance 100-600 ohms? If yes, go to step 6 . If no, go to next step.
4. Turn ignition switch to OFF position. Leave the PCM disconnected. Disconnect the ICM harness connector. Test the IC timing control circuit for an open. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
5. Test for an intermittent and poor connections at the ICM. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
6. Test for an intermittent and poor connection at the PCM. Did you find and correct the condition? If yes, go to step 9 . If no, go to step 8 .
7. Replace the ICM. After repair, go to step 9 .
8. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
9. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
10. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1352: IGNITION BYPASS CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Ignition Control Module (ICM) has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consists of the following circuits

1. The Ignition Control (IC) timing signal.
2. The IC timing control.
3. The low resolution engine speed signal.
4. The low reference signal.

The ICM sends 3X signals to the PCM and controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions occur

1. The PCM receives the second 3X signal.
2. The PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

If the PCM detects an open in the IC timing control circuit, DTC P1352 sets.

The engine is running.

1. The PCM detects an open circuit in the IC timing signal circuit.
2. The condition is present for 300 3X reference periods, 106 crankshaft revolutions.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Measure the resistance between the Ignition Control (IC) timing control and the Ignition Control Module (ICM) low reference circuits. Turn ignition switch to RUN position, engine OFF. Probe the IC timing signal circuit using a test light connected to battery voltage. Is the resistance 6-10 k/ohms? If yes, go to step 6 . If no, go to next step.
4. Turn ignition switch to OFF position. Leave the PCM disconnected. Disconnect the ICM harness connector. Test the ICM IC timing signal circuit for an open. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
5. Test for an intermittent and poor connection at the ICM. Did you find and correct the condition? If yes, go to step 9 . If no, go to step 7 .
6. Test for an intermittent and poor connection at the PCM. Did you find and correct the condition? If yes, go to step 9 . If no, go to step 8 .
7. Replace the ICM. After repair, go to step 9 .
8. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
9. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
10. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1361: IGNITION CONTROL CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Ignition Control Module (ICM) has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consist of the following circuits

1. The Ignition Control (IC) timing signal.
2. The IC timing control.
3. The low-resolution engine speed signal.
4. A low reference signal.

The ICM sends 3x signals to the PCM. The ICM controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

1. The PCM receives the second 3x signal.
2. The PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

If the PCM does not detect IC pulses while IC mode spark advance is commanded, DTC P1361 sets.

1. The engine speed is more than 600 RPM.
2. DTC P1351 did not set.

1. The PCM does not detect IC pulses while IC mode spark advance is commanded.
2. The condition is present for 300 3X reference periods, 100 crankshaft revolutions.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Is DTC P1362 also set? If yes, go to step 6 . If no, go to next step.
4. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM). Turn ignition switch to RUN position, engine OFF. Probe the Ignition Control Module (ICM) Ignition Control (IC) timing control circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 5 . If no, go to step 16 .
5. Turn ignition switch to OFF position. Leave the PCM disconnected. Disconnect the ICM harness connector. Turn ignition switch to RUN position, engine OFF. Probe the ICM IC timing control circuit using a test light connected to ground. Does the test light illuminate? If yes, go to step 12 . If no, go to step 10 .
6. Turn ignition switch to OFF position. Disconnect the ICM. Probe the IC timing control circuit at the PCM using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 13 . If no, go to next step.
7. Leave the ignition switch in OFF position. Leave the ICM disconnected. Probe the IC timing signal circuit of the ICM using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 14 . If no, go to next step.
8. Leave the ignition switch in OFF position. Leave the PCM disconnected. Leave the ICM disconnected. Test for a short between the IC timing control and IC timing signal circuits. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
9. Leave the ignition switch in OFF position. Connect the ICM. Leave the PCM disconnected. Turn ignition switch to RUN position, engine OFF. Measure the resistance between the IC timing control circuit of the ICM and a good ground. Observe the DMM while probing the IC timing signal circuit of the ICM using a test light connected to battery positive voltage. Does the resistance switch between 100-600 ohms to 6-10 k/ohms? If yes, go to step 11 . If no, go to next step.
10. Test for shorted terminals or poor connections at the ICM. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 15 .
11. Test for shorted terminals or poor connections at the PCM. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 16 .
12. Repair the short to voltage in the IC timing control circuit of the ICM. After repair, go to step 17 .
13. Repair the short to ground in the low reference circuit in the IC timing control circuit of the ICM. After repair, go to step 17 .
14. Repair the short to ground in the low reference circuit in the IC timing signal circuit of the ICM. After repair, go to step 17 .
15. Replace the ICM. After repair, go to step 17 .
16. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
17. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
18. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1362: IGNITION CONTROL CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Ignition Control Module (ICM) has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consist of the following circuits

1. The Ignition Control (IC) timing signal.
2. The IC timing control.
3. The low-resolution engine speed signal.
4. A low reference signal.

The ICM sends 3x signals to the PCM. The ICM controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

1. The PCM receives the second 3x signal.
2. The PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

If the PCM detects a short to voltage in the IC timing signal circuit, DTC P1362 sets.

The engine is running.

1. The PCM detects a short to voltage in the IC timing signal circuit.
2. The condition is present for 300 3X reference periods, 100 crankshaft revolutions.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Is DTC P1361 also set? If yes, go to step 6 . If no, go to next step.
4. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM). Turn ignition switch to OFF position, engine OFF. Probe the Ignition Control Module (ICM) Ignition Control (IC) timing control circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 11 .
5. Turn ignition switch to OFF position. Leave the PCM disconnected. Disconnect the ICM harness connector. Turn ignition switch to RUN position, engine OFF. Probe the IC timing control circuit of the ICM using a test light connected to ground. Does the test light illuminate? If yes, go to step 12 . If no, go to step 10 .
6. Turn ignition switch to OFF position. Disconnect the ICM. Probe the IC timing control circuit at the PCM using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 13 . If no, go to next step.
7. Leave the ignition switch in OFF position. Leave the ICM disconnected. Probe the IC timing signal circuit of the ICM using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 14 . If no, go to next step.
8. Leave the ignition switch in OFF position. Leave the PCM disconnected. Leave the ICM disconnected. Test for a short between the IC timing control and IC timing signal circuits. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
9. Leave the ignition switch in OFF position. Connect the ICM. Leave the PCM disconnected. Turn ignition switch to RUN position, engine OFF. Measure the resistance between the IC timing control circuit of the ICM and a good ground. Observe the DMM while probing the IC timing signal circuit of the ICM using a test light connected to battery positive voltage. Does the resistance switch between 100-600 ohms to 6-10 k/ohms? If yes, go to step 11 . If no, go to next step.
10. Test for shorted terminals or poor connections at the ICM. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 15 .
11. Test for shorted terminals or poor connections at the PCM. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 16 .
12. Repair the short to voltage in the IC timing control circuit of the ICM. After repair, go to step 17 .
13. Repair the short to ground in the low reference circuit in the IC timing control circuit of the ICM. After repair, go to step 17 .
14. Repair the short to ground in the low reference circuit in the IC timing signal circuit of the ICM. After repair, go to step 17 .
15. Replace the ICM. After repair, go to step 17 .
16. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
17. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
18. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1374: CKP HIGH TO LOW RESOLUTION FREQUENCY CORRELATION

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

A 3X reference signal is produced by the Ignition Control Module (ICM). The ICM calculates the 3X reference signal by dividing the Crankshaft Position (CKP) sensor 7X pulses by 2 when the engine is running and the CKP synchronizing pulses are being received. The Powertrain Control Module (PCM) uses the 3X reference signal to calculate the engine RPM and the CKP at engine speeds above 1600 RPM. The PCM also uses these pulses to initiate injector pulses. The PCM compares the 3X reference pulses to the 24X CKP pulses and the Camshaft Position (CMP) pulses. The PCM will use the 24X CKP reference circuit for fuel and ignition control. The engine will continue to start and run using only the 24X CKP and CMP sensor signals. If the PCM detects an incorrect number of pulses on the low resolution engine speed signal circuit, DTC P1374 sets.

The engine is running, and the 24X reference pulses are being received.

1. The ratio of 24X reference pulses to 3X reference pulses received by the PCM does not equal 8.
2. The ratio of 24X reference pulses to CMP PCM input pulses received by the PCM equals 48.
3. The conditions are present for more than 10 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Attempt to start the engine. Does the engine start and run? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Does the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
4. Turn ignition switch to OFF position. Disconnect Control Module (ICM) harness connector. Remove the injector fuse. Turn ignition switch to RUN position, engine OFF. Momentarily probe the low resolution engine speed signal circuit at the ignition module harness connector using a test light connected to battery voltage. Observe the ENGINE SPEED parameter using a scan tool. Is an Engine Speed displayed? If yes, go to step 8 . If no, go to step 6 .
5. Did the test light illuminate? If yes, go to step 8 . If no, go to next step.
6. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position, engine OFF. Test the ICM low resolution engine speed signal circuit for an open, a short to voltage or high resistance. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 9 .
7. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Test the low resolution engine speed signal circuit of the ICM for a short to ground or for high resistance. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 9 .
8. Test for an intermittent and for a poor connection at the ICM. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace the ICM. After repair, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

DTC P1374 can be caused by secondary components leaking high voltage into the IC module. Check for the following conditions

1. Incorrect harness routing near secondary ignition components.
2. Ignition coil arcing to wiring harness or IC module. Check the ignition coils for cracks, carbon tracking or other signs of damage.
3. Secondary ignition wires arcing to the wiring harness.
4. If the DTC is determined to be intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1380: MISFIRE DETECTED - ROUGH ROAD DATA NOT AVAILABLE (CENTURY & MALIBU)

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) detects engine misfire events by monitoring variations in the crankshaft rotation speed. Wheel speed changes caused by rough road conditions can cause changes in crankshaft speed. By monitoring the wheel speed sensors, the Anti-Lock Brake System (ABS) can determine if the vehicle is operating on a rough road. If the ABS is detecting a rough road condition severe enough to affect misfire detection, a rough road signal is sent to the PCM on the serial data circuit. If DTC P0300 is set and the rough road information is not available due to an ABS malfunction, DTC P1380 will set.

1. The vehicle speed is more than 10 MPH.
2. The engine load is less than 87 percent.
3. The engine misfire is detected and DTC P0300 set.
4. The engine speed is less than 5000 RPM.

An ABS malfunction exists preventing the PCM from receiving rough road detection data.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to DIAGNOSTIC SYSTEM CHECK - ABS in appropriate ANTI-LOCK BRAKES article.

DTC P1381: MISFIRE DETECTED NO EBTCM/PCM SERIAL DATA (CENTURY & MALIBU)

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) detects engine misfire events by monitoring variations in the crankshaft rotation speed. Wheel speed changes caused by rough road conditions can cause changes in crankshaft speed. By monitoring the wheel speed sensors, the Anti-Lock Brake System (ABS) can determine if the vehicle is operating on a rough road. If the ABS is detecting a rough road condition severe enough to affect misfire detection, a rough road signal is sent to the PCM on the serial data circuit. If DTC P0300 is set and the rough road information is not available due to an ABS malfunction, DTC P1381 will set.

1. The vehicle speed is more than 10 MPH.
2. The engine load is less than 87 percent.
3. The engine misfire is detected and DTC P0300 set.
4. The engine speed is less than 5000 RPM.

1. Serial data malfunction exists preventing the PCM from receiving rough road detection data.
2. The above condition is met for 5 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number on the diagnostic procedure.

1. 1 - This step will diagnose a malfunction in the serial data.

Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to DIAGNOSTIC SYSTEM CHECK - ABS in appropriate ANTI-LOCK BRAKES article.

The Exhaust Gas Recirculation (EGR) valve position sensor is monitored by the Powertrain Control Module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. When the ignition switch is turned to RUN position, the PCM records the EGR Learned Minimum Position. The PCM compares the EGR Learned Minimum Position parameter to the EGR Position Sensor parameter. If the PCM detects that the EGR valve is still open when the PCM is commanding the EGR valve closed, DTC P1404 sets.

1. The engine is running.
2. The Ignition 1 Signal voltage parameter is 11-18 volts.
3. The EGR valve is commanded to zero percent for 20 seconds after the EGR valve has been commanded to open more than 40 percent for 0.5 second.

1. The EGR Position Sensor parameter is 0.2 volt more than the EGR Learned Minimum Position parameter when the Desired EGR Position parameter is commanded to zero percent for 20 seconds.
2. The EGR Position Sensor parameter is more than 40 percent and is steady for 0.5 seconds after a test failure and before the next test will be run.
3. The above conditions are met 4 times.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

The number below refers to the step number on the diagnostic procedure.

1. 1 - This step verifies that the malfunction is present.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P1635 also set? If yes, go to «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) or «DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p1635-5-volt-reference-1-circuit) . If no, go to next step.
3. Start the engine. Observe the EGR Position Sensor parameter using a scan tool. Is the EGR position sensor parameter less than one percent? If yes, go to next step. If no, go to step 6 .
4. Turn ignition switch to RUN position, engine OFF. Command the EGR valve from zero percent to 100 percent using a scan tool. Is the EGR Position Variance parameter less than 15 percent? If yes, go to next step. If no, go to step 7 .
5. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
6. Turn ignition switch to OFF position. Disconnect the EGR valve. Turn ignition switch to RUN position, engine OFF. Observe the EGR Position Sensor parameter using a scan tool. Is the EGR Position Sensor parameter less than one percent? If yes, go to next step. If no, go to step 10 .
7. Connect a test light between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve. Does the test light illuminate? If yes, go to next step. If no, go to step 9 .
8. Connect a 3-amp fused jumper wire from the EGR valve 5-volt reference circuit to the EGR valve position signal circuit. Is the EGR position sensor parameter on the scan tool more than 99 percent? If yes, go to step 14 . If no, go to step 12 .
9. Connect a test light between the 5-volt reference circuit of the EGR valve and a good ground. Does the test light illuminate? If yes, go to step 11 . If no, go to step 13 .
10. Test the EGR valve position signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
11. Test the EGR valve position sensor low reference circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
12. Test the EGR valve position signal circuit for high resistance or for a high resistance short to ground. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
13. Test the 5-volt reference circuit of the EGR valve for an open or for high resistance. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 15 .
14. Test for an intermittent and for a poor connection at the EGR valve. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
15. Test all 5-volt reference circuits for a short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
16. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 18 .
17. Replace the EGR valve. After repair, go to step 19 .
18. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
19. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
20. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. Check for excessive deposits on the EGR valve pintle or seat. Remove the EGR valve and check for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
2. If the problem is intermittent, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1441: EVAPORATIVE EMISSION SYSTEM FLOW DURING NON-PURGE

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

This DTC tests for undesired intake manifold vacuum flow to the Evaporative Emission (EVAP) system. The PCM seals the EVAP system by commanding the EVAP canister purge valve Closed and the EVAP canister vent valve Closed. The PCM monitors the Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If vacuum in the EVAP system is more than a predetermined value within a predetermined time, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE VALVE/VENT VALVE RELATIONSHIP table.

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1106, P1107, P1112, P1114, P1115, P1121 or P1122 are not set.
2. The ignition voltage is 10-18 volts.
3. The Barometric Pressure (BARO) sensor parameter is more than 75 kPa.
4. The Fuel Level sensor parameter is 15-85 percent.
5. The Engine Coolant Temperature (ECT) sensor parameter is 39-86°F (4-30°C).
6. The Intake Air Temperature (IAT) sensor parameter is 39°-86°F (4-30°C).
7. The start-up ECT and IAT are within 16°F (9°C) of each other.
8. The Vehicle Speed Sensor (VSS) parameter is less than 75 MPH.

The PCM detects vacuum during a non-purge condition.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Perform the Service Bay Test. See «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to step 8 . If no, go to next step.
3. Turn ignition switch to OFF position. Disconnect the purge line from the EVAP purge solenoid. Turn ignition switch to RUN position, engine OFF. Is the FTP sensor parameter -1 to 1 in. H2O? If yes, go to next step. If no, go to step 5 .
4. Connect a hand held vacuum gauge to the EVAP purge port. Disconnect the EVAP canister purge valve harness connector. Monitor vacuum on the vacuum gauge. Start the engine and allow the engine to idle. Increase the idle to 1200-1500 RPM. Does the vacuum gauge indicate an increase in vacuum? If yes, go to step 7 . If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
5. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
6. Replace the FTP sensor. After repair, go to step 8 .
7. Replace the EVAP canister purge solenoid. After repair, go to next step.
8. Perform the Service Bay Test. See «SERVICE BAY TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to next step. If no, go to step 3 .
9. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. The EVAP system tests run when the engine is first started and meets the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . An intermittent condition could be caused by an improperly installed or damaged EVAP canister purge solenoid, or by a temporary blockage in the EVAP canister purge solenoid.
2. For intermittent conditions, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (CENTURY & GRAND PRIX)

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) provides 5 volts to the following sensors

1. The Manifold Absolute Pressure (MAP) sensor.
2. The Exhaust Gas Recirculation (EGR) valve.
3. The Throttle Position (TP) sensor.
4. The Exhaust Gas Recirculation (EGR) valve position sensor (Grand Prix only)

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects the voltage is out of tolerance, DTC P1635 sets.

The engine is running.

1. The PCM detects a voltage out of tolerance condition on the 5-volt reference circuit.
2. The condition is met for more than 10 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Turn ignition switch to OFF position. Disconnect Exhaust Gas Recirculation (EGR) valve. Turn ignition switch to RUN position, engine OFF. Command the EGR valve to 100 percent using a scan tool. Measure the voltage from the 5-volt reference circuit of the EGR valve to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step 5 . If no, go to next step.
4. Is the voltage more than 5.2 volts? If yes, go to step 8 . If no, go to step 6 .
5. Connect the EGR valve. Disconnect the Manifold Absolute Pressure (MAP) sensor harness connector. Command the EGR valve to 100 percent using a scan tool. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go to step 10 .
6. Monitor the DMM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. If the voltage changes when one of the devices is disconnected, replace the component. Did you replace a component? If yes, go to step 12 . If no, go to next step.
7. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Test the 5-volt reference circuits for a short to ground or any sensor low reference circuit. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
8. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position, engine OFF. Test all the 5-volt reference circuits' the MAP sensor signal circuit and on Grand Prix, the FTP sensor signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 12 . If no, go to next step.
9. On all models, check for a short between the EGR 5-volt reference circuit and the EGR solenoid control high circuit. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace the EGR valve. After repair, go to step 12 .
11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
12. On all Models, using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
13. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. If any sensor using a 5-volt bias voltage, such as the Intake Air Temperature (IAT) sensor or fuel level sensor, is shorted to voltage, DTC P1639 may set in addition to DTC P1635.
2. For intermittent conditions, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT (MALIBU)

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) provides 5 volts to the following sensors

1. The Manifold Absolute Pressure (MAP) sensor.
2. The Exhaust Gas Recirculation (EGR) valve.
3. The Throttle Position (TP) sensor.
4. The Exhaust Gas Recirculation (EGR) valve position sensor (Grand Prix only)

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects the voltage is out of tolerance, DTC P1635 sets.

The engine is running.

1. The PCM detects a voltage out of tolerance condition on the 5-volt reference circuit.
2. The condition is met for more than 10 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
3. Turn ignition switch to OFF position. Disconnect the Exhaust Gas Recirculation (EGR) valve position sensor harness connector. Turn ignition switch to RUN position, engine OFF. Command the EGR solenoid to 100 percent using a scan tool. Measure the voltage from the 5-volt reference circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step 5 . If no, go to next step.
4. Is the voltage measured in the previous step more than 5.2 volts? If yes, go to step 8 . If no, go to step 6 .
5. Connect the EGR valve harness connector. Disconnect the Manifold Absolute Pressure (MAP) sensor. Command the EGR solenoid to 100 percent using a scan tool. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . If no, go to step 11 .
6. Monitor a DMM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. If voltage changes when one of the devices are disconnected (MAP, FTP or TP sensors), replace the component. Was a component replaced? If yes, go to step 13 . If no, go to next step.
7. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
8. Monitor the DMM while disconnecting the MAP sensor and FTP sensor, one at a time. If the voltage returns to within 4.8-5.2 volts when one of the devices are disconnected, test that sensors signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
9. Test the 5-volt reference circuits for a short to voltage. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
10. Test for a short between the EGR 5-volt reference circuit and the EGR control high circuit. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
11. Replace the EGR valve. After repair, go to step 13 .
12. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
13. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
14. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. If any sensor using a 5-volt bias voltage, such as the Intake Air Temperature (IAT) sensor or fuel level sensor, is shorted to voltage, DTC P1639 may set in addition to DTC P1635.
2. For intermittent conditions, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1639: 5-VOLT REFERENCE 2 CIRCUIT (CENTURY)

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) provides 5 volts to the following sensors

1. The Air Conditioning (A/C) pressure sensor.
2. The Fuel Tank Pressure (FTP) sensor.

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuit. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P1639 sets.

The engine is running.

1. The Powertrain Control Module (PCM) detects a voltage out of tolerance condition on the 5-volt reference circuit.
2. The condition is present for longer than 2 seconds.

1. The Powertrain Control Module (PCM) illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The Powertrain Control Module (PCM) turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition cycle? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Turn ignition switch to OFF position. Disconnect the Air Conditioning (A/C) pressure sensor harness connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the 5-volt reference circuit of the A/C pressure sensor to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step 5 .
4. Connect the A/C pressure sensor. Disconnect the Fuel Tank Pressure (FTP) sensor. Measure the voltage from the 5-volt reference circuit of the FTP sensor to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step 12 .
5. Is the voltage measured in the previous step more than 5.2 volts? If yes, go to step 8 . If no, go to next step.
6. Monitor the DMM while disconnecting the FTP sensor. Does the voltage return to 4.8-5.2 volts when the FTP sensor is disconnected? If yes, go to step 11 . If no, go to next step.
7. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
8. Monitor the DMM while disconnecting the FTP sensor. Does the voltage return to 4.8-5.2 volts when the FTP sensor is disconnected? If yes, go to step 10 . If no, go to next step.
9. Test all 5-volt reference circuits for a short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
10. Test the FTP sensor signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
11. Replace the FTP sensor. After repair, go to step 14 .
12. Replace the A/C pressure sensor. See REFRIGERANT PRESSURE SENSOR in appropriate AIR CONDITIONING & HEATING article. After repair, go to step 14 .
13. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
15. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. If any sensor using a 5-volt bias voltage, such as the Intake Air Temperature (IAT) sensor or fuel level sensor, is shorted to voltage, DTC P1635 may set in addition to DTC P1639.
2. For intermittent conditions, Go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1639: 5-VOLT REFERENCE 2 CIRCUIT (GRAND PRIX & MALIBU)

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Powertrain Control Module (PCM) provides 5 volts to the Air Conditioning (A/C) pressure sensor. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P1639 sets.

The engine is running.

1. The PCM detects a voltage out of tolerance condition on the 5-volt reference circuit.
2. The condition is present for longer than 10 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) .
3. Turn ignition switch to OFF position. Disconnect the Air Conditioning (A/C) pressure sensor. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the A/C pressure sensor 5-volt reference circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step 9 . If no, go to next step.
4. Is the voltage measured in the previous step more than 5.2 volts? If yes, go to next step. If no, go to step 8 .
5. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM) harness connectors. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the 5-volt reference circuit of the A/C pressure sensor to a good ground using a DMM. Is the voltage more than zero volts? If yes, go to next step. If no, go to step 7 .
6. Test the 5-volt reference circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 11 .
7. Test the 5-volt reference circuit for a short to any other circuit within the harness to the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
8. Turn ignition switch to RUN position. Disconnect the PCM harness connectors. Test the 5-volt reference circuit for a short to ground or a short to any other circuit within the harness to the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace the A/C pressure sensor. After repair, go to step 11 .
10. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
11. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
12. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

1. If any sensor using a 5-volt bias voltage, such as the Intake Air Temperature (IAT) sensor or fuel level sensor, is shorted to voltage, DTC P1635 may set in addition to DTC P1639.
2. For intermittent conditions, Go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1640: PCM OUTPUT "A" CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). The ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. The ODM 1 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the ignition 1 input. Any incorrect current on a circuit to the ODM will cause the ODM to report this DTC.

The ignition switch is in RUN position.

1. The ODM has detected a voltage greater than 33 volts.
2. Or, excessive current is detected on any circuit to the ODM.
3. The conditions are present for 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0560 set? If yes, diagnose engine electrical system. Go to appropriate GENERATORS & REGULATORS article in ELECTRICAL. If no, go to next step.
3. Using a scan tool, select the OUTPUT DRIVER DATA list. Observe the parameters on the scan tool. Do any parameters indicate a fault present? If yes, go to next step. If no, go to step 5 .
4. Test for a short to voltage on the control circuit of the component that indicated a fault. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
5. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
6. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
7. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

An over charging condition may set this DTC. Check charging system. See appropriate GENERATORS & REGULATORS in ELECTRICAL.

Thoroughly inspect any circuitry suspected of causing the intermittent complaint. Repair the circuits as necessary. Go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1650: PCM OUTPUT "B" CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). The ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. The ODM 2 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the battery input. Any incorrect current on a circuit to the ODM will cause the ODM to report this DTC.

The ignition switch is in RUN position.

1. The ODM has detected a voltage greater than 33 volts.
2. Or, excessive current is detected on any circuit to the ODM.
3. The conditions are present for 30 seconds.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The PCM turns OFF the Malfunction Indicator Light (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0560 set? If yes, diagnose engine electrical system. Go to appropriate GENERATORS & REGULATORS article in ELECTRICAL. If no, go to next step.
3. Using a scan tool, select the OUTPUT DRIVER DATA list. Observe the parameters on the scan tool. Do any parameters indicate a fault present? If yes, go to next step. If no, go to step 5 .
4. Test for a short to voltage on the control circuit of the component that indicated a fault. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
5. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
6. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
7. Using the scan tool, observe the stored information in CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

An over charging condition may set this DTC. Check charging system. See appropriate GENERATORS & REGULATORS in ELECTRICAL.

Thoroughly inspect any circuitry suspected of causing the intermittent complaint. Repair the circuits as necessary. Go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1660: PCM OUTPUT "C" CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). The ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. The ODM 3 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the ignition 1 input. Any incorrect current on a circuit to the ODM will cause the ODM to report this DTC.

The ignition switch is in RUN position.

1. The ODM has detected a voltage greater than 33 volts.
2. Or, excessive current is detected on any circuit to the ODM.
3. The conditions are present for 30 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0560 set? If yes, diagnose engine electrical system. See appropriate GENERATORS & REGULATORS article in ELECTRICAL. If no, go to next step.
3. Using a scan tool, select the OUTPUT DRIVER DATA list. Observe the parameters on the scan tool. Do any parameters indicate a fault present? If yes, go to next step. If no, go to step 5 .
4. Test for a short to voltage on the control circuit of the component that indicated a fault. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
5. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
6. Use scan tool to clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
7. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay at this time.

An over charging condition may set this DTC. Check charging system. See appropriate GENERATORS & REGULATORS in ELECTRICAL.

Thoroughly inspect any circuitry suspected of causing the intermittent complaint. Repair the circuits as necessary. Go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

DTC P1670: PCM OUTPUT "D" CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

The Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). The ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. The ODM 4 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the ignition 1 input. Any incorrect current on a circuit to the ODM will cause the ODM to report this DTC.

The ignition switch is in RUN position.

1. The ODM has detected a voltage greater than 33 volts.
2. Or, excessive current is detected on any circuit to the ODM.
3. The condition is present for 30 seconds.

1. The PCM stores the DTC information into memory when the diagnostic runs and fails.
2. The Malfunction Indicator Light (MIL) will not illuminate.
3. The PCM records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
4. The Driver Information Center (DIC), if equipped, may display a message.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear DTC using a scan tool.

1. Perform diagnostic system check - engine controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
2. Is DTC P0560 set? If yes, diagnose engine electrical system. See appropriate GENERATORS & REGULATORS article in ELECTRICAL. If no, go to next step.
3. Using a scan tool select the Output Driver Data list. Observe the parameters on the scan tool. Do any parameters indicate a fault present? If yes, go to next step. If no, go to step 5 .
4. Test for a short to voltage on the circuit to the component that indicated a fault. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
5. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING. After replacing PCM, go to next step.
6. Use scan tool to clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running Test. See «CONDITIONS FOR RUNNING TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
7. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) . If no, system is okay.

An over charging condition may set this DTC. Check charging system. See appropriate GENERATORS & REGULATORS in ELECTRICAL.

Thoroughly inspect any circuitry suspected of causing the intermittent complaint. Repair the circuits as necessary. Go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

CENTURY

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

GRAND PRIX

See ENGINE PERFORMANCE under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

MALIBU

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

See also:
• NO-START DIAGNOSIS
• TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU
• INTERMITTENTS
• MANIFOLD ABSOLUTE PRESSURE SENSOR
• EXHAUST RESTRICTION
• EXHAUST SYSTEM CHECK
• EMISSION SYSTEMS & SUB-SYSTEMS
• FUEL SYSTEM DIAGNOSIS
• EXHAUST GAS RECIRCULATION
• ELECTRONIC IGNITION SYSTEM DIAGNOSIS
• EXHAUST LEAKAGE
• DIAGNOSTIC STARTING POINT - ENGINE CONTROLS
• DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS
• DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683 OR P2610: ECU MALFUNCTION
• DIAGNOSTIC TROUBLE CODE DEFINITIONS
• MIL INOPERATIVE
• MIL ALWAYS ON
• SERVICE PROGRAMMING SYSTEM REMOTE PROCEDURE
• SERVICE PROGRAMMING SYSTEM PASS-THRU PROCEDURE
• SERVICE PROGRAMMING SYSTEM OFF BOARD REMOTE PROCEDURE
• SERVICE PROGRAMMING SYSTEM OFF BOARD PASS-THRU PROCEDURE
• CKP SYSTEM VARIATION LEARN PROCEDURE
• DTC P1336: CRANKSHAFT POSITION SYSTEM VARIATION NOT LEARNED
• INSPECTION/MAINTENANCE SYSTEM DTCS
• CONDITIONS FOR RUNNING TEST (COLD START)
• CONDITIONS FOR RUNNING TEST
• CONDITIONS FOR RUNNING
• P0030
• P0103
• P0107
• P0108
• P0112
• P0113
• P0116
• P0117
• P0118
• P0122
• P0123
• P0125
• P0128
• P0130
• P0131
• P0132
• P0133
• P0134
• P0135
• P0137
• P0138
• P0140
• P0141
• P0171
• P0172
• P0201-P0206
• P0300
• P0325
• P0327
• P0336
• P0341
• P0401
• P0403
• P0404
• P0405
• P0420
• P0440
• P0442
• P0443
• P0446
• P0449
• P0452
• P0453
• P0506
• P0507
• P0650
• P1106
• P1107
• P1111
• P1112
• P1114
• P1115
• P1121
• P1122
• P1133
• P1134
• P1351
• P1352
• P1361
• P1362
• P1374
• P1380
• P1381
• P1441
• P1635
• P1639
• P1640
• P1650
• P1660
• P1670
• CODE TYPES