Home ReviewsRefund
Home/Pontiac/Firebird/Pontiac Firebird IV (1993-2002)/Repair manual/Testing & Diagnostics/Engine Control System - Tests W/codes - 3.8L: Diagnosis
Contents Wiring diagrams Section: Testing & Diagnostics All sections

Engine Control System - Tests W/codes - 3.8L: Diagnosis Pontiac Firebird IV

Testing & Diagnostics ~42853 words

SELF-DIAGNOSTIC SYSTEM

Note. For On-Board Diagnostic System Check see the BASIC TESTING - 3.8L article.

Note. Powertrain Control Module (PCM) may also be referred to as Vehicle Control Module (VCM) in some diagnostic text and illustrations. Terms may be used interchangeably.

PCM/VCM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, PCM/VCM will store a Diagnostic Trouble Code (DTC) and, in most cases, illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. Malfunctions are recorded as hard failures or as intermittent failures.

There are 4 types of DTC category

  1. Type "A" - Emissions related, turns on MIL the first time DTC sets.
  2. Type "B" - Emissions related, turns on MIL if fault is active for 2 consecutive driving cycles.
  3. Type "C" - Non-emissions related, does not turn on MIL, but will turn on SERVICE light.
  4. Type "D" - Non-emissions related, does not turn on MIL or SERVICE light.

DTC INFO MODE

Used to search for a specific type of stored DTC information. There are 7 choices in this mode. Technician may be instructed to test DTC(s) in a certain manner. Follow the affected DTC test procedures. To get complete description of any status, hit ENTER key before pressing the desired F-key.

DTC STATUS

This selection will display any DTC(s) that have not run during the current ignition cycle or have reported a test failure during this ignition up to a maximum of 33 DTCs. DTC test which run and passed will cause that affected DTC to be removed from scan tool screen.

LAST TEST FAIL

This selection will display only DTCs that have failed the last time the test ran. The last test may have ran during the previous ignition cycle, if a type "A" or "B" DTC is displayed. For type "C" DTCs, the last failure must have occurred during the current ignition cycle to be displayed as LAST TEST FAIL.

TEST FAIL SCC

Test Fail Since Code Clear selection will display all active and history DTCs that have reported a test failure since the last time DTCs were cleared. DTCs that last failed over 40 warm-up cycles before this option is selected will not be displayed.

TEST RAN AND PASSED

This message indicates the selected diagnostic test has

  1. Passed the last test.
  2. Ran and passed during this ignition cycle.
  3. Ran and passed since DTCs were last cleared.
  4. Test has not failed since DTCs were last cleared.

If this message is displayed, repair is done. If FAILED THIS IGN. message is displayed, repair is incomplete and further diagnosis is required.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order

  1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK must be performed before using specific DTC testing procedure. See the «BASIC TESTING - 3.8L»(ref-20653) article.
  2. If DTC(s) were displayed, determine whether codes are hard or intermittent trouble codes. Hard codes will cause MIL to illuminate continuously while engine is running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(ref-20509-S28325113342001010200000) . For diagnosing hard codes, proceed to appropriate DTC test. For diagnosing intermittent codes, proceed to INTERMITTENTS in the TESTS W/O CODES article.
  3. If no DTCs are present and a driveability problem exists, refer to SYMPTOMS in the TESTS W/O CODES article. Doing so will help identify proper system or component to check in the SYSTEM/COMPONENT TESTS article.
  4. After necessary repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation and ensure DTC does not reset.

READING TROUBLE CODES

Note. Use of Tech 1 or 2 scan tool is required to retrieve DTCs. Refer to user reference manuals supplied with scan tool.

TROUBLE CODE DEFINITIONS

Code No.Circuit Affected
P0101MAF System Performance
P0102MAF Sensor Circuit-Low Frequency
P0103MAF Sensor Circuit-High Frequency
P0107MAP Sensor Circuit Low Voltage
P0108MAP Sensor Circuit High Voltage
P0112IAT Sensor Circuit Low Voltage
P0113IAT Sensor Signal Voltage High
P0117ECT Sensor Circuit Low Voltage
P0118ECT Sensor Signal High Voltage
P0121TP Sensor System Performance
P0122TP Sensor Circuit Low Voltage
P0123TP Sensor Circuit High Voltage
P0125ECT Excessive Time To Closed Loop
P0131HO2S Circuit Low Voltage-Sensor 1
P0132HO2S 1 Circuit High Voltage
P0133HO2S Slow Response-Sensor 1
P0134HO2S Insufficient Activity-Sensor 1
P0135HO2S Heater Circuit-Sensor 1
P0137HO2S 2 Circuit High Voltage
P0140HO2S Insufficient Activity-Sensor 2
P0141HO2S Heater Circuit-Sensor 2
P0143HO2S Circuit Low Voltage-Bank 1, Sensor 3
P0144HO2S Circuit High Voltage-Bank 1, Sensor 3
P0146HO2S Circuit Insufficient Activity-Bank 1, Sensor 3
P0147HO2S Heater Circuit-Bank 1, Sensor 3
P0151HO2S Circuit Low Voltage-Bank 2, Sensor 1
P0152HO2S Circuit High Voltage-Bank 2, Sensor 1
P0153HO2S Slow Response-Bank 2, Sensor 1
P0154HO2S Circuit Insufficient Activity-Bank 2, Sensor 1
P0155HO2S Heater Circuit-Bank 2, Sensor 1
P0171Fuel Trim System Lean-Bank 1
P0172Fuel Trim System Rich
P0174Fuel Trim System Lean-Bank 2
P0175Fuel Trim System Rich-Bank 2
P0300Engine Misfire Detected
P0301Engine Misfire Detected
P0302Engine Misfire Detected
P0303Engine Misfire Detected
P0304Engine Misfire Detected
P0305Engine Misfire Detected
P0306Engine Misfire Detected
P0307Engine Misfire Detected
P0308Engine Misfire Detected
P0325Knock Sensor Module Circuit
P0326Knock Sensor High Voltage
P0327Knock Sensor Low Voltage
P033618X Reference Signal Circuit
P0341CMP Sensor Circuit
P0401EGR System Insufficient Flow
P0420TWC System Low Efficiency
P0441EVAP System-No Flow During Purge
P0500VSS Circuit-M/T
P0506IAC System RPM Low
P0507RPM Out Of Range &/Or IAC Valve IAC System RPM High
P0530A/C Refrigerant Pressure Sensor Circuit
P0560System Voltage
P0601PCM Memory
P0602PCM Not Programmed
P0704Clutch Switch Circuit
P1106MAP Sensor Circuit Intermittent High Voltage
P1107MAP Sensor Circuit Intermittently Low Voltage
P1111IAT Sensor Circuit Intermittent High Voltage
P1112IAT Sensor Circuit Intermittent Low Voltage
P1114ECT Sensor Circuit Intermittent Low Voltage
P1115ECT Sensor Circuit Intermittent High Voltage
P1121TP Sensor Intermittently High Voltage
P1122TP Sensor Intermittent Low Voltage
P1133HO2S Insufficient Switching-Sensor 1
P1134HO2S Transition Time Ratio-Bank 1, Sensor 1
P1153HO2S Insufficient Switching-Bank 2, Sensor 1
P1154HO2S Transition Time Ratio-Bank 2, Sensor 1
P1200Injector Control Circuit
P1336CKP System Variation Not Learned
P1350Ignition Control Circuit
P1361IC Circuit Not Toggling
P13743X Reference Circuit
P1380EBTCM DTC Detected Rough Road Data Unusable
P1441EVAP Control System Flow During Non-Purge
P1554Cruise Control Status Circuit
P1626Theft Deterrent System Fuel Enable Circuit
P1629Theft Deterrent System-Cranking Signal Malfunction
P16355-Volt Reference "A" Circuit
P16395-Volt Reference "B" Circuit
P1641MIL Control Circuit
P1651Fan No. 1 Relay Control Circuit
P1652Fan No. 2 Relay Control Circuit
P1654A/C Relay Control Circuit
P1655EVAP Purge Solenoid Control Circuit
P1662Cruise Control Inhibit Control Circuit
P1663Generator Light Control Circuit

TROUBLE CODE DEFINITION

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if DTC(s) are hard failure codes or intermittent failure codes. Diagnostic procedures will not always help analyze intermittent codes. To determine hard codes and intermittent codes

  1. Enter diagnostic mode. Read and record all stored DTCs. Exit diagnostic mode, and clear DTCs. See «CLEARING DIAGNOSTIC TROUBLE CODES (DTC)»(ref-20509-S07875881582001010200000) .
  2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. MIL should go out. Operate warm engine at specified RPM for 2 minutes and note MIL.
  3. If MIL illuminates, enter diagnostic mode. Read and record DTCs. This will reveal hard failure codes. Oxygen sensor related codes may require a road test to reset hard failure after DTCs were cleared.
  4. If MIL does not illuminate, all stored DTCs were intermittent failures, except as noted above. NOTE: DTCs will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some DTCs may not set in a service bay operational mode and may require road testing vehicle in order to duplicate conditions under which code will set.

CLEARING DIAGNOSTIC TROUBLE CODES (DTC)

To clear DTCs from memory, either to determine if malfunction will occur again or after making necessary repairs, disconnect power supply to ECM/PCM/VCM for at least 30 seconds or clear codes using a scan tool.

Diagnostic Aids

Diagnostic aids are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A scan tool plugged into DLC is used to read DTCs and check voltages in system on serial data line. A scan tool is REQUIRED to retrieve vehicle information.

Computerized engine control system is most easily diagnosed using scan tool; however, other tools may aid in diagnosing problems. These tools are a tachometer, test light, ohmmeter, digital voltmeter with a 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic test. In addition, special jumper harnesses or testers may be required by manufacturer to facilitate diagnosis.

SCAN TOOL USAGE

Note. Before connecting scan tool to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK located in the BASIC TESTING - 3.8L article. If vehicle does not pass OBD system check, information received may be invalid.

Scan tool is a specialized tester which, when plugged into 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 cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA . 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/VCM; 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. About 80 percent of driveability problems occur without DTCs. Sensors that are out of calibration will not set a DTC but will cause driveability problems.

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. See SCAN DATA.

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.

DIAGNOSTIC TROUBLE CODES

Note. Before clearing DTCs, perform On-Board Diagnostic (OBD) System Check. See the BASIC TESTING - 3.8L article. Record FREEZE FRAME and FAILURE RECORDS for reference during testing. Data will be erased when DTCs are cleared. If PCM/VCM is replaced, NEW PCM/VCM must be programmed using special manufacturer's equipment.

Diagnostic Procedures

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If DTC P1635 is also set, go to «DTC P1635»(ref-20509-S01348100382001010200000) . If DTC is not set, go to next step.
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0101 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0101 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Turn ignition on. Observe MAP and BARO parameter on scan tool. If reading is 65-105 kPa, go to next step. If not, go to step 8).
  5. Start engine. Observe MAP sensor display on scan tool with engine idling. If display is 29-48 kPa, go to next step. If not, go to step 7).
  6. Observe MAP sensor display on scan tool while slowly increasing engine speed to 3000 RPM. If MAP value increases with increase in RPM, go to step 9). If not, go to step 8).
  7. Check for throttle body inlet screen blockage. Check for vacuum leaks at intake manifold, throttle body, or EGR valve flange and pipes. Check for PCV valve faulty, missing or incorrectly installed. Repair faulty conditions as necessary. After repairs, go to step 22). If no faulty conditions exist, go to step 9).
  8. Replace MAP sensor. After replacing sensor, go to step 22).
  9. Turn ignition on, throttle closed. Using scan tool, read THROTTLE AT IDLE. If scan tool displays YES, go to next step. If scan tool does not display YES, go to «DTC P0121»(ref-20509-S09725176542001010200000) .
  10. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on, engine off. Using a DVOM, check voltage between MAF sensor harness connector signal circuit and chassis ground. If voltage is about 5 volts, go next step. If voltage is not as specified, go to step 12).
  11. Connect a test light between MAF sensor harness connector ignition feed and ground circuits. If test light illuminates, go to step 15). If test light does not illuminate, go to step 14).
  12. If voltage is less than 4.5 volts, go to step 16). If voltage is not less than 4.5 volts, go to next step.
  13. Turn ignition off. Disconnect PCM connectors. Turn ignition on, with engine off. Check voltage between PCM harness connector MAF signal circuit and chassis ground. If voltage reading is zero volts, go to step 21). If voltage is not zero volts, go to step 19)
  14. Connect test light between MAF sensor harness connector ignition feed circuit and chassis ground. If test light illuminates, go to step 17). If test light does not illuminate, go to step 18).
  15. Check for faulty connection at MAF sensor. Repair as necessary. After repairs, go to step 22). If connection is okay, go to step 20).
  16. Check MAF sensor signal circuit between PCM and MAF sensor for open or short. Repair signal circuit as necessary. After repairs, go to step 22). If signal circuit is okay, go to step 21).
  17. Locate and repair open MAF in the sensor ground circuit. After repairs, go to step 22).
  18. Locate and repair open MAF sensor ignition feed circuit. After repairs, go to step 22).
  19. Locate and repair short to voltage in MAF sensor signal circuit. After repairs, go to step 22).
  20. Replace MAF sensor. After replacing sensor, go to step 22).
  21. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  22. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0101. If scan tool displays DTC P0101 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0101 FAILED THIS IGN, repair is complete.

Check for skewed or stuck Throttle Position (TP) sensor. Using scan tool, read TP ANGLE value with throttle closed. If value is not zero percent, check for and repair the following condition(s)

  1. Throttle plate sticking or excessive deposits on throttle plate or throttle bore.
  2. TP sensor signal circuit shorted to voltage.
  3. Faulty connection or high resistance in TP sensor ground circuit.

If none of the listed conditions exist and TP ANGLE value is not zero percent, replace TP sensor.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

Check for plugged intake air duct or dirty air filter. A wide-open throttle acceleration from a stop should cause MAF reading on scan tool to increase from about 4-7 grams per second at idle to 100 grams per second or greater at time of 1-2 shift. If not, check for restriction.

Check for a skewed MAP sensor, which can cause Barometric (BARO) pressure reading to be incorrectly calculated. This condition may also cause high Idle Air Control (IAC) counts. If IAC counts are high, replace MAP sensor.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. Start engine. With engine at idle, use scan tool to read MAF FREQUENCY. If frequency is less than 1200 Hz, go to step 4). If frequency is not less than 1200 Hz, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0102 FAILED THIS IGN, go to next step. If DTC P0102 FAILED THIS IGN is not displayed, see DIAGNOSTIC AIDS.
  4. Check for MAF sensor inlet screen blockage. Check for vacuum leaks at intake manifold, throttle body or EGR valve flange and pipes. Check for PCV valve faulty, missing or incorrectly installed. Repair faulty conditions as necessary. After repairs, go to step 14). If no faulty conditions exist, go to next step.
  5. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on, engine off. Using a DVOM, check voltage between MAF sensor harness connector signal circuit and chassis ground. If voltage reading is about 5 volts, go next step. If voltage reading is not about 5 volts, go to step 9).
  6. Connect a test light between MAF sensor harness connector ignition feed and ground circuits. If test light illuminates, go to step 8). If test light does not illuminate, go to next step.
  7. Connect test light between MAF sensor harness connector ignition feed circuit and battery ground. If test light illuminates, go to step 10). If test light does not illuminate, go to step 11).
  8. Check for faulty connection at MAF sensor. Repair connection as necessary. After repairs, go to step 14). If connection is okay, go to step 12).
  9. Check MAF sensor signal circuit between PCM and MAF sensor for open or short. Repair signal circuit as necessary. After repairs, go to step 14). If signal circuit is okay, go to step 13).
  10. Locate and repair open in the MAF sensor ground circuit. After repairs, go to step 14).
  11. Locate and repair open MAF sensor ignition feed circuit. After repairs, go to step 14).
  12. Replace MAF sensor. After replacing sensor, go to step 14).
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0102. If scan tool displays DTC P0102 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0102 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

Check for plugged intake air duct or filter element. Check minimum airflow rate as follows

  1. Run engine and allow it to reach operating temperature.
  2. Disconnect IAC valve and install IAC Driver (J37027).
  3. With engine idling, command IAC valve to fully extended position (zero counts).
  4. Using scan tool, observe MASS AIRFLOW VALUE.
  5. If MAF value is less than 2.27 grams per second, clean or replace throttle body as necessary.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine. With engine at idle, use scan tool to read MAF FREQUENCY. If frequency is greater than 10,500 Hz, go to step 4). If frequency is less than specified, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0103 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0103 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  4. Turn ignition off. Disconnect MAF sensor harness connector. Turn engine on and allow it to idle. Using scan tool, read MAF FREQUENCY. If frequency is zero Hz, go to next step. If frequency is not as specified, go to step 7).
  5. Check for faulty connection at MAF sensor. Repair connection as necessary. After repairs, go to step 10). If connection is okay, go to next step.
  6. Replace MAF sensor. After replacing sensor, go to step 10).
  7. Ensure MAF sensor harness is not routed too close to high-voltage wires, such as spark plug cables, ignition coils or other high voltage components. Reroute harness if necessary. After repairs, go to step 10). If harness routing is okay, go to next step.
  8. Check MAF sensor signal circuit connection at PCM. Repair connection as necessary. After repairs, go to step 10). If connection is okay, go to next step.
  9. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  10. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0103. If scan tool displays DTC P0103 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0103 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read LAST TEST FAIL. If scan tool displays DTC P0107 and «DTC P1406»(ref-20509-S23982525182001010200000) , inspect and repair common circuit(s). If scan tool does not display P0107 and P1406, go to next step.
  3. Turn ignition off. Turn ignition on, engine off. Using scan tool, read MAP sensor voltage. If voltage is about zero volts, go to step 5). If voltage is not about zero volts, go to next step.
  4. With ignition on, engine off, use scan tool to read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0107 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0107 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Disconnect MAP sensor harness connector. Connect a jumper wire between MAP sensor harness connector 5-volt reference circuit and signal circuit. If scan tool voltage is about 4.95 volts, go to step 11). If voltage is not about 4.95 volts, go to next step.
  6. Turn ignition off. Remove jumper wire. Connect a test light between MAP sensor harness connector signal circuit and battery voltage. Turn ignition on. If voltage is now about 4.95 volts, go to next step. If voltage is not about 4.95 volts, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Check PCM harness connector 5-volt reference circuit for open or short to ground. If open or short is found, repair as necessary. After repairs, go to step 13). If circuit is okay, go to next step.
  8. Check for faulty connection of 5-volt reference circuit at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  9. Turn ignition off. Disconnect PCM connectors. Check PCM harness connector MAP signal circuit for open or short to ground. If open or short is found, repair as necessary. After repairs, go to step 13). If no open or short is found, go to next step.
  10. Check for faulty connection of MAP signal circuit at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  11. Replace MAP sensor. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  13. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0107. If scan tool displays DTC P0107 FAILED THIS IGN, return to step 3). If scan tool does not display DTC P0107 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read LAST TEST FAIL. If scan tool displays DTC P0123 and «DTC P1406»(ref-20509-S23982525182001010200000) , check and repair common circuits. If scan tool does not display «DTC P0123»(ref-20509-S12962672392001010200000) and DTC P1406, go to next step.
  3. Correct any engine idle or vacuum problems before proceeding. Turn engine on and allow it to idle. Using scan tool, read MAP sensor voltage. If voltage is greater than 3.5 volts, go to step 5). If voltage is not greater than 3.5 volts, go to next step.
  4. With ignition still on and with engine off, use scan tool to read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0108 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0108 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. If voltage is zero volts, go to next step. If voltage is not zero volts, go to step 7).
  6. Connect a test light between MAP sensor harness connector ground circuit and battery voltage. If test light illuminates, go to step 8). If test light does not illuminate, go to step 10).
  7. Check MAP sensor harness connector signal circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 17). If short to voltage is not found, go to step 12).
  8. Check for faulty connection of ground circuit at MAP sensor. If faulty connection is found, repair as necessary. After repairs, go to step 17). If connection is okay, go to next step.
  9. Check for plugged or leaking vacuum supply to MAP sensor. If vacuum supply is okay, go to step 13). If vacuum supply is not okay, go to step 16).
  10. Check for faulty MAP sensor ground circuit connection at PCM. If connection is faulty, repair as necessary. After repairs, go to step 17). If connection is okay, go to next step.
  11. Check continuity of MAP sensor ground circuit. If resistance is 5 ohms or greater, repair circuit as necessary. After repairs, go to step 17). If resistance is not 5 ohms or greater, go to step 12).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 17).
  13. Turn ignition off. Disconnect PCM connectors. Turn ignition on, engine off. Check PCM harness connector 5-volt reference circuit for short to voltage. If short is found, repair as necessary. After repairs, go to step 17). If circuit is okay, go to next step.
  14. Check for faulty connection at MAP sensor. If faulty connection is found, repair as necessary. After repairs, go to step 17). If connection is okay, go to next step.
  15. Replace MAP sensor. After replacing sensor, go to step 17).
  16. Repair faulty vacuum source. After repairs, go to next step.
  17. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0108. If scan tool displays DTC P0108 FAILED THIS IGN, return to step 3). If scan tool does not display DTC P0108 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on. Using scan tool, read INTAKE AIR TEMP. If temperature is greater than 266°F (130°C), go to step 4). If temperature is not greater than 266°F (130°C), go to next step.
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0112 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0112 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect IAT sensor harness connector. Using scan tool, read INTAKE AIR TEMP. If IAT sensor temperature is less than -36°F (-39°C), go to step 6). If temperature is not less than -36°F (-39°C), go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Check IAT sensor signal circuit for short to ground. If short is found, go to step 7). If no short is found, go to step 8).
  6. Replace IAT sensor. After replacing sensor, go to step 9).
  7. Repair IAT sensor signal circuit. After repairs, go to step 9).
  8. Replace PCM. Program replacement PCM using required equipment. After replacing and reprogramming PCM, go to next step.
  9. Turn ignition on, with engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0112. If scan tool displays DTC P0112 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0112 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed IAT sensor. See IAT TEMPERATURE-TO-RESISTANCE VALUES .

Temperature °F (°C)Ohms
212 (100)177
194 (90)241
158 (70)467
122 (50)973
104 (40)1459
86 (30)2238
68 (20)3520
50 (10)5670

IAT TEMPERATURE-TO-RESISTANCE VALUES

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on. Using scan tool, read INTAKE AIR TEMP. If temperature is less than -38°F (-39°C), go to step 4). If temperature is not less than -38°F (-39°C), go to next step.
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0113 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0113 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect IAT sensor harness connector. Connect a jumper wire between IAT sensor harness connector signal and ground circuits. Using scan tool, read INTAKE AIR TEMP. If temperature is 284°F (140°C) or greater, go to step 6). If not, go to next step.
  5. Connect jumper wire between chassis ground and IAT sensor harness connector signal circuit. Using scan tool, read INTAKE AIR TEMP. If temperature is 284°F (140°C) or greater, go to step 7). If not, go to step 8).
  6. Check for faulty connection at IAT sensor. If faulty connection is found, repair as necessary. After repairs, go to step 12). If connection is okay, go to step 10).
  7. Turn ignition off. Disconnect PCM connectors. Check IAT sensor ground circuit for an open. If open is found, repair as necessary. After repairs, go to step 12). If circuit is okay, go to step 9).
  8. Turn ignition off. Disconnect PCM connectors. Check IAT signal circuit for an open. If open is found, repair circuit as necessary. After repairs, go to step 12). If no open is found, go to next step.
  9. Check for faulty IAT signal or ground circuit connection at PCM. If problem is found, repair as necessary. After repairs, go to step 12). If no problem is found, go to step 11).
  10. Replace IAT sensor. After replacing sensor, go to step 12).
  11. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  12. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0113. If scan tool displays DTC P0113 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0113 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

If DTC cannot be duplicated, the information included in the Fail Records data can be used in determining vehicle mileage since DTC was last set.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on. Using scan tool, read ENG COOL TEMP. If temperature is 282°F (139°C) or greater, go to step 4). If not, go to next step.
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0117 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0117 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect ECT sensor harness connector. Using scan tool, read ENG COOL TEMP. If temperature is -38°F (-39°C) or less, go to step 6). If temperature is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Check ECT sensor signal circuit for short to ground. If short is found, repair as necessary. After repairs, go to step 8). If circuit is okay, go to step 7).
  6. Replace ECT sensor. After replacing sensor, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0117. If scan tool displays DTC P0117 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0117 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor.

If DTC cannot be duplicated, the information included in the Fail Records data can be used in determining vehicle mileage since DTC was last set.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on. Using scan tool, read ENG COOL TEMP. If temperature is -36°F (-38°C) or less, go to step 4). If not, go to next step.
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0118 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0118 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  4. Disconnect ECT sensor harness connector. Connect a jumper wire between ECT sensor harness connector signal and ground circuits. Using scan tool, read ENG COOL TEMP. If temperature is 284°F (140°C), go to step 6). If temperature is not as specified, go to next step.
  5. Connect jumper wire between chassis ground and ECT sensor harness connector signal circuit. Using scan tool, read ENG COOL TEMP. If temperature is 284°F (140°C), go to step 7). If temperature is not as specified, go to step 8).
  6. Check for faulty connection at ECT sensor. If faulty connection is found, repair as necessary. After repairs, go to step 12). If connection is okay, go to step 10).
  7. Turn ignition off. Disconnect PCM connectors. Check ECT sensor ground circuit for an open. If open is found, repair as necessary. After repairs, go to step 12). If circuit is okay, go to step 9).
  8. Turn ignition off. Disconnect PCM connectors. Check ECT signal circuit for an open. If open is found, repair as necessary. After repairs, go to step 12). If circuit is okay, go to next step.
  9. Check for faulty ECT signal or ground circuit connection at PCM. If problem is found, repair as necessary. After repairs, go to step 12). If no problem is found, go to step 11).
  10. Replace ECT sensor. After replacing sensor, go to step 12).
  11. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  12. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0118. If scan tool displays DTC P0118 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0118 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor.

If DTC cannot be duplicated, the information included in the Fail Records data can be used in determining vehicle mileage since DTC was last set.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If «DTC P1635»(ref-20509-S01348100382001010200000) is also set, go to that DTC. If not, turn ignition on, engine off. Using scan tool, read MAP value. If value is less than 65 kPa, go to next step. If not, go to step 6).
  3. Disconnect MAP sensor harness connector. Connect a test light between MAP sensor harness connector 5-volt reference and signal circuits. Using scan tool, read MAP value. If value is less than 65 kPa, go to step 5). If not, go to next step.
  4. Check MAP sensor signal circuit for open or short between PCM and MAP sensor. If problem is found, repair as necessary. After repairs, go to step 13). If no problem is found, go to step 12).
  5. Replace MAP sensor. After replacing sensor, go to step 13).
  6. Observe scan tool TP ANGLE value while moving throttle from closed to wide open throttle. If value increases steadily and evenly from closed to open throttle, see DIAGNOSTIC AIDS. If value does not increase as specified, go to next step.
  7. Disconnect TP sensor harness connector. If TP voltage is zero volts, go to next step. If not, go to step 9).
  8. Connect a test light between TP sensor harness connector 5-volt reference and signal circuits. Using scan tool, read TP sensor voltage. If scan tool voltage is 5 volts, go to step 11). If voltage is not as specified, go to step 10).
  9. Check TP sensor signal circuit for short to ground, ground circuit for high resistance and poor connection. Repair as necessary and go to step 13). If no problem is found, go to step 12).
  10. Check TP sensor 5-volt reference circuit for poor connection or high resistance between PCM and TP sensor. Repair as necessary and go to step 13). If no problem is found, go to step 12).
  11. Replace TP sensor. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  13. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for «DTC P0117»(ref-20509-S27543127092001010200000) . If scan tool displays DTC P0117 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0117 FAILED THIS IGN, repair is complete.

Check for and repair the following condition(s)

  1. Throttle plate sticking or excessive deposits on throttle plate or throttle bore.
  2. Check TP sensor harness connector terminals for damage.
  3. A steady throttle movement from a stop should cause TP ANGLE value reading on scan tool to increase smoothly as throttle is opened.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed MAP signal or faulty MAP sensor.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read LAST TEST FAIL. If scan tool displays DTC P0107 and «DTC P1406»(ref-20509-S23982525182001010200000) , check and repair common circuits. If scan tool does not display «DTC P0107»(ref-20509-S19896188752001010200000) and DTC P1406, go to next step.
  3. Turn ignition off. Turn ignition on, engine off. With throttle closed, use scan tool to read TP sensor voltage. If voltage is less than 0.16 volt, go to step 5). If voltage is not less than 0.16 volt, go to next step.
  4. With ignition still on, engine off, use scan tool to read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0122 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0122 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Disconnect TP sensor harness connector. Connect a jumper wire between TP sensor harness connector 5-volt reference and signal circuits. If scan tool voltage reading is 5 volts, go to step 11). If not, go to next step.
  6. Turn ignition off. Remove jumper wire. Connect a test light between TP sensor harness connector signal circuit and battery voltage. If scan tool voltage reading is 5 volts, go to next step. If not, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Check PCM harness connector 5-volt reference circuit for open or short to ground. If open or short is found, repair as necessary. After repairs, go to step 14). If circuit is okay, go to next step.
  8. Turn ignition off. Check for faulty connection of 5-volt reference circuit at PCM. If faulty connection is found, repair connection as necessary. After repairs, go to step 14). If connection is okay, go to step 13).
  9. Turn ignition off. Disconnect PCM connectors. Check PCM harness connector TP signal circuit for open or short to ground. If open or short is found, repair as necessary. After repairs, go to step 14). If circuit is okay, go to next step.
  10. Check for faulty connection of TP signal circuit at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 14). If connection is okay, go to step 13).
  11. Check for faulty connection of TP signal circuit at TP sensor. If faulty connection is found, repair as necessary. After repairs, go to step 14). If connection is okay, go to step 13).
  12. Replace TP sensor. After replacing sensor, go to step 14).
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0122. If scan tool displays DTC P0122 FAILED THIS IGN, return to step 3). If scan tool does not display DTC P0122 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read LAST TEST FAIL. If scan tool displays DTC P0108 and «DTC P1406»(ref-20509-S23982525182001010200000) , check and service common circuits. If scan tool does not display «DTC P0108»(ref-20509-S27088437472001010200000) and DTC P1406, go to next step.
  3. Turn ignition on, engine off. Using scan tool, read TP sensor voltage. If voltage is greater than 4.71 volts, go to step 5). If voltage is not greater than 4.71 volts, go to next step.
  4. Turn ignition on, with engine off. Use scan tool to read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0123 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0123 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Disconnect TP sensor harness connector. If voltage is about zero volt, go to next step. If voltage is not as specified, go to step 7).
  6. Connect a test light between TP sensor harness connector ground circuit and battery voltage. If test light illuminates, go to step 8). If test light does not illuminate, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Check TP sensor harness connector signal circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 14). If circuit is okay, go to step 13).
  8. Turn ignition on. While monitoring scan tool TP SENSOR display, disconnect each component (one at a time) that shares common 5-volt reference circuit. If display changes, replace component that causes change. After repairs, go to step 14). If display does not change, go to next step.
  9. Turn ignition off. Disconnect PCM connectors. Turn ignition on, engine off. Check PCM harness connector 5-volt reference circuit for short to voltage. If short is found, repair as necessary. After repairs, go to step 14). If no short is found, go to next step.
  10. Check for faulty connection at TP sensor. If faulty connection is found, repair as necessary. After repairs, go to step 14). If connection is okay, go to next step.
  11. Turn ignition off. Disconnect PCM connectors. Check for faulty TP sensor ground circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 14). If connection is okay, go to next step.
  12. Replace TP sensor. After replacing sensor, go to step 14).
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0123. If scan tool displays DTC P0123 FAILED THIS IGN, return to step 3). If scan tool does not display DTC P0123 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high-voltage wires, such as spark plug cables. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

Turn ignition on, engine off. Using scan tool TP SENSOR display, slowly depress accelerator to wide open throttle. If voltage is greater than 4.71 volts at any time, replace TP sensor.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Allow engine to cool completely. Turn engine on and allow it to idle. Using scan tool, monitor ENG COOL TEMP. If temperature increases to 70°F (21°C) within 2 minutes, see DIAGNOSTIC AIDS. If specified temperature is not reached within 2 minutes, go to next step.
  3. If any ECT DTCs are set, diagnose affected DTC before proceeding. If no ECT DTCs are set, go to next step.
  4. Allow engine to cool. Turn ignition on and observe cooling fans. If cooling fans are off, go to next step. If cooling fans are on, diagnose and repair cooling fan problem.
  5. Check coolant level. If coolant level is low, go to step 9) If coolant level is okay, go to next step.
  6. Check thermostat operation. If thermostat is operating correctly, go to next step. If thermostat is not operating correctly, go to step 9).
  7. Compare actual coolant temperature with scan tool ECT value. If temperatures are within 5°F (3°C) of each other, go to step 9). If temperatures are not within 5°F (3°C) of each other, go to next step.
  8. Check for high resistance in wiring related to ECT sensor and for poor connections at ECT sensor and PCM. If a problem is found with connections, go to step 10). If no problem is found, go to step 11).
  9. Repair cooling system as necessary. After repairs, go to step 12).
  10. Repair as necessary. After repairs, go to step 12).
  11. Replace ECT sensor. After replacing sensor, go to next step.
  12. Allow engine to cool completely. Using scan tool, clear DTCs. Turn engine on and allow it to idle. Using scan tool, monitor ENG COOL TEMP. If temperature increases to 70°F (21°C) within 2 minutes, repair is complete. If specified temperature is not reached within 2 minutes, return to step 2).

Check coolant level. Ensure thermostat and cooling fans are operating properly. Check for high resistance in wiring related to ECT sensor. Check for skewed ECT sensor by comparing actual coolant temperature with scan tool display, and replace ECT sensor if temperatures are not close.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 1 voltage. If voltage stays less than 0.3 volt, go to step 4). If voltage does not stay less than 0.3 volt, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0131 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0131 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 1 connector. Connect jumper wire between HO2S 1 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Check HO2S sensor harness connector signal circuit for short to ground. If short is found, go to next step. If no short is found, go to step 7).
  6. Repair circuit as necessary. After repairs, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0131. If scan tool displays DTC P0131 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0131 FAILED THIS IGN, repair is complete.

Ensure HO2S 1 sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Perform A-6, FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform A-7, INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check for vacuum leaks at intake manifold, throttle body, EGR system and crankcase ventilation system. Check for exhaust leaks in front of HO2S 1. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor. Check for fuel contamination. See BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. If no faults are found, replace HO2S 1.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 1 voltage. If voltage stays greater than 0.8 volt, go to step 5). If voltage does not stay at greater than 0.8 volt, go to next step.
  3. Operate vehicle in deceleration fuel mode (vehicle speed greater than 25 MPH and TP ANGLE less than 3%) while monitoring HO2S 1 voltage. If voltage stays greater than 0.11 volt, go to step 5). If voltage does not stay at greater than 0.11 volt, go to next step.
  4. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0132 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0132 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Disconnect HO2S 1 connector. Connect a jumper wire between HO2S 1 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  6. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector HO2S 1 signal circuit and chassis ground. If voltage is greater than 0.6 volt, go to next step. If voltage is not greater than 0.6 volt, go to step 8).
  7. Repair short to voltage in HO2S 1 signal circuit. After repairs, go to step 9).
  8. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  9. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0132. If scan tool displays DTC P0132 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0132 FAILED THIS IGN, repair is complete.

Ensure HO2S 1 sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 1 signal or ground circuits. Check for internally shorted HO2S 1. Check HO2S 1 for silicon (powdery white deposit) contamination. Check for faulty PCM grounds. See BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check EVAP canister for fuel saturation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor. Check for fuel in fuel pressure regulator vacuum line.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other HO2S DTCs (except P0153, P1133, P1134, P1135, P1136, P1153, P1155 or P1156) are set, diagnose affected DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0133 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  3. If scan tool also displays DTC P0153, P1133, P1134, P1135, P1136, P1153, P1154, P1155 and/or P1156 FAILED THIS IGN, go to step 8). If scan tool does not display these DTCs, go to next step.
  4. Visually inspect exhaust system for leaks near HO2S 1. If leaks are found, repair as necessary. After repairs, return to step 2). If no leaks are found, go to next step.
  5. Visually inspect HO2S 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S 1 and PCM. Check for damaged wiring. If a problem is found, go to step 9). If no problem is found, go to next step.
  6. Disconnect HO2S 1 connector. Connect a jumper wire betweenHO2S 1 harness connector ground circuit and chassis ground. Using scan tool, read HO2S 1 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 10).
  7. Connect a jumper wire between HO2S 1 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.3 volt, go to step 12). If voltage is not less than 0.3 volt, go to step 11).
  8. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After replacing sensor, go to step 13).
  9. Repair condition as necessary. After repairs, go to step 13).
  10. Repair open HO2S 1 ground circuit or HO2S 1 signal circuit shorted to ground. After repairs, go to step 13).
  11. Repair open HO2S 1 signal circuit or faulty PCM connections as necessary. After repairs, go to step 13).
  12. Replace HO2S 1. After replacing sensor, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0133. If scan tool displays DTC P0133 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0133 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Place gear selector in Park or Neutral, and apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 1 voltage. If voltage is varying outside of 0.4-0.5 volt range, go to next step. If not, go to step 4)
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0134 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0134 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Connect a jumper wire between HO2S 1 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.15 volt, go to step 8). If voltage is not less than 0.15 volt, go to next step.
  5. Remove jumper wire. Using DVOM, check voltage between HO2S 1 harness connector signal and heater ground circuits. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 7).
  6. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 1 harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection and go to step 13). If resistance is not greater than 5 ohms, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 1 harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13). If resistance is not greater than 5 ohms, go to step 10).
  8. Check for faulty connection at HO2S 1. If faulty connection is found, repair as necessary. After repairs, go to step 13). If no faulty connection is found, go to step 11).
  9. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If no faulty connection is found, go to step 12).
  10. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If no faulty connection is found, go to step 12).
  11. Replace HO2S 1. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0134. If scan tool displays DTC P0134 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0134 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check HO2S 1 heater operation.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step. NOTE: If engine has been operating, allow engine to cool for about 30 minutes before proceeding with tests.
  2. Turn ignition on, with engine off. Using scan tool, read HO2S 1 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  3. Inspect HO2S 1 ignition feed fuse. If fuse is open, go to step 15). If fuse is okay, go to next step.
  4. Turn ignition off. Raise and support vehicle. Disconnect HO2S 1 harness connector. Connect a test light between ground and HO2S 1 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  5. Connect test light between HO2S 1 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
  6. Allow HO2S 1 to cool for at least 10 minutes. Using DVOM, check resistance between ignition feed and heater ground circuits at HO2S 1. If resistance is 3-10 ohms, go to step 9). If resistance is not as specified, go to step 14).
  7. Repair open in HO2S 1 ignition feed circuit. After repairs, go to step 16).
  8. Repair open in HO2S 1 heater ground circuit. After repairs, go to step 16).
  9. Check for faulty connection at HO2S 1. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  10. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 1 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16). If resistance is 5 ohms or less, go to next step.
  11. Check for faulty connection at HO2S 1 harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  12. Check for faulty ground circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  13. Check for faulty HO2S 1 signal circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  14. Replace HO2S 1. After replacing sensor, go to step 16).
  15. Locate and repair short to ground in HO2S 1 ignition feed circuit, replace fuse. After repairs, go to next step.
  16. Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 1 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, repair is complete. If voltage is not as specified, return to step 2).

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 2 voltage. If voltage stays less than 0.075 volt, go to step 4). If voltage does not stay less than 0.075 volt, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0137 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0137 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 2 connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Check HO2S 2 sensor harness connector signal circuit for short to ground. If short is found, go to next step. If no short is found, go to step 7).
  6. Repair circuit as necessary. After repairs, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0137. If scan tool displays DTC P0137 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0137 FAILED THIS IGN, repair is complete.

Ensure HO2S 2 sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Perform FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check for vacuum leaks at intake manifold, throttle body, EGR system and crankcase ventilation system. Check for exhaust leaks in front of HO2S 2. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor. Check for fuel contamination. See FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 2 voltage. If voltage stays greater than 999 mV, go to step 4). If voltage does not stay at greater than 999 mV, go to next step.
  3. Turn ignition on. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0138. If scan tool displays DTC P0138 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0138 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector HO2S 2 signal circuit and chassis ground. If voltage is greater than 999 mV, go to next step. If voltage is not greater than 999 mV, go to step 7).
  6. Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0138. If scan tool displays DTC P0138 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0138 FAILED THIS IGN, repair is complete.

Ensure HO2S 2 sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 2 signal or ground circuits. Check for internally shorted HO2S 2. Check HO2S 2 for silicone (powdery white deposit) contamination. Check for faulty PCM grounds. See BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check EVAP canister for fuel saturation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor. Check for fuel in fuel pressure regulator vacuum line.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start and warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 2 voltage. If voltage is not switching from greater than 0.475 to less than 0.425 volt, go to next step. If voltage is switching as specified, go to step 4).
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0140 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0140 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.15 volt, go to step 8). If voltage is not less than 0.15 volt, go to next step.
  5. Remove jumper wire. Using DVOM, check voltage between HO2S 2 harness connector signal and heater ground circuits. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 7).
  6. Turn ignition off. Disconnect PCM harness connectors. Check resistance of HO2S 2 harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection. After repairs, go to step 13). If resistance is not greater than 5 ohms, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 2 harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13). If resistance is not greater than 5 ohms, go to step 10).
  8. Check for faulty connection at HO2S 2. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 11).
  9. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  10. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  11. Replace HO2S No. 2. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0140. If scan tool displays DTC P0140 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0140 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check HO2S 2 heater operation.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step. NOTE: If engine has been operating, allow engine to cool for about 30 minutes before proceeding with tests.
  2. Turn ignition on, engine off. Using scan tool, read HO2S 2 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  3. Inspect HO2S 2 ignition feed fuse. If fuse is open, go to step 15). If fuse is okay, go to next step.
  4. Turn ignition off. Raise and support vehicle. Disconnect HO2S 2 harness connector. Connect a test light between ground and HO2S 2 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  5. Connect test light between HO2S 2 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
  6. Allow HO2S 2 to cool for at least 10 minutes. Using DVOM, check resistance between ignition feed and heater ground circuits at HO2S 2. If resistance is 3-10 ohms, go to step 9). If resistance is not as specified, go to step 14).
  7. Repair open HO2S 2 ignition feed circuit. After repairs, go to step 16).
  8. Repair open HO2S 2 heater ground circuit. After repairs, go to step 16).
  9. Check for faulty connection at HO2S 2. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  10. Turn ignition off. Disconnect PCM harness connectors. Check resistance of HO2S 2 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16). If resistance is 5 ohms or less, go to next step.
  11. Check for faulty connection at HO2S 2 harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  12. Check for faulty ground circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  13. Check for faulty HO2S 2 signal circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  14. Replace HO2S 2. After replacing sensor, go to step 16).
  15. Locate and repair short to ground in HO2S 2 ignition feed circuit, replace fuse and go to next step.
  16. Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 2 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, repair is complete. If voltage is not as specified, return to step 2).

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 3 voltage. If voltage stays less than 0.075 volt, go to step 4). If not, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0143 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0143 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 3 connector. Connect jumper wire between HO2S 3 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Check HO2S 3 sensor harness connector signal circuit for short to ground. If short is found, go to next step. If circuit is okay, go to step 7).
  6. Repair circuit as necessary. After repairs, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0143. If scan tool displays DTC P0143 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0143 FAILED THIS IGN, repair is complete.

Ensure HO2S 3 sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Perform A-6, FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform A-7, INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check for vacuum leaks at intake manifold, throttle body, EGR system and crankcase ventilation system. Check for exhaust leaks in front of HO2S 3. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor. Check for fuel contamination. See BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 3 voltage. If voltage stays greater than .999 volt, go to step 4). If voltage does not stay at greater than .999 volt, go to next step.
  3. Turn ignition on. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0144. If scan tool displays DTC P0144 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0144 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 3 connector. Connect a jumper wire between HO2S 3 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector HO2S 3 signal circuit and chassis ground. If voltage is greater than .999 volt, go to next step. If voltage is not greater than .999 volt or less, go to step 7).
  6. Repair short to voltage in HO2S 3 signal circuit. After repairs, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0144. If scan tool displays DTC P0144 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0144 FAILED THIS IGN, repair is complete.

Ensure HO2S 3 sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 3 signal or ground circuits. Check for internally shorted HO2S 3. Check HO2S 3 for silicone (powdery white deposit) contamination. Check for faulty PCM grounds. Perform FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check EVAP canister for fuel saturation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor. Check for fuel in fuel pressure regulator vacuum line.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 3 voltage. If voltage is not switching from greater than 0.475 to less than 0.425 volt, go to next step. If voltage is switching as specified, go to step 4)
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0146 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0146 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S 3 harness connector. Connect a jumper wire between HO2S 3 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.15 volt, go to step 8). If voltage is not less than 0.15 volt, go to next step.
  5. Remove jumper wire. Using DVOM, check voltage between HO2S 3 harness connector signal and heater ground circuits. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 7).
  6. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 3 harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13). If resistance is not greater than 5 ohms, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 3 harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13). If resistance is not greater than 5 ohms, go to step 10).
  8. Check for faulty connection at HO2S 3. If faulty connection is found, repair as necessary. After repairs, go to step 13). If sensor connection is okay, go to step 11).
  9. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If PCM connection is okay, go to step 12).
  10. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  11. Replace HO2S 3. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0146. If scan tool displays DTC P0146 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0146 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check HO2S 3 heater operation.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step. NOTE: If engine has been operating, allow engine to cool for about 30 minutes before proceeding with tests.
  2. Turn ignition on, engine off. Using scan tool, read HO2S 3 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  3. Inspect HO2S 3 ignition feed fuse. If fuse is open, go to step 15). If fuse is okay, go to next step.
  4. Turn ignition off. Raise and support vehicle. Disconnect HO2S 3 harness connector. Connect a test light between chassis ground and HO2S 3 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  5. Connect test light between HO2S 3 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
  6. Allow HO2S 3 to cool for at least 10 minutes. Using DVOM, check resistance between ignition feed and heater ground circuits at HO2S 3. If resistance is 3-10 ohms, go to step 9). If resistance is not as specified, go to step 14).
  7. Repair open HO2S 3 ignition feed circuit. After repairs, go to step 16).
  8. Repair open HO2S 3 heater ground circuit. After repairs, go to step 16).
  9. Check for faulty connection at HO2S 3. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  10. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S 3 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16). If resistance is not greater than 5 ohms, go to next step.
  11. Check for faulty connection at HO2S 3 harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  12. Check for faulty ground circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  13. Check for faulty HO2S 3 signal circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  14. Replace HO2S 3. After replacing sensor, go to step 16).
  15. Locate and repair short to ground in HO2S 3 ignition feed circuit, replace fuse and go to next step.
  16. Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 3 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, repair is complete. If voltage is not as specified, return to step 2).

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Warm engine to operating temperature. Run vehicle under conditions required to set DTC. Using scan tool, read HO2S voltage. If voltage stays less than 0.3 volt, go to step 4). If voltage does not stay less than 0.3 volt, go to next step.
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0151 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0151 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect HO2S connector. Connect a jumper wire between HO2S harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  5. Turn ignition off. Disconnect PCM connectors. Check HO2S sensor harness connector signal circuit for short to ground. If short is found, go to next step. If circuit is okay, go to step 7).
  6. Repair circuit as necessary. After repairs, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0151. If scan tool displays DTC P0151 FAILED THIS IGN, return to step 2). If not, repair is complete.

Ensure HO2S sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Perform FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S voltage. If voltage stays at greater than 0.8 volt, go to step 5). If voltage does not stay at greater than 0.8 volt, go to next step.
  3. Operate vehicle in deceleration fuel mode (vehicle speed more than 25 MPH and TP ANGLE less than 3 percent) while monitoring HO2S 4 voltage. If voltage stays at greater than 0.11 volt, go to step 5). If voltage does not stay at greater than 0.11 volt, go to next step.
  4. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0152 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0152 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Disconnect HO2S connector. Connect a jumper wire between HO2S harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see DIAGNOSTIC AIDS. If voltage is not as specified, go to next step.
  6. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector HO2S 4 signal circuit and chassis ground. If voltage is greater than 0.6 volt, go to next step. If voltage is not greater than 0.6 volt, go to step 8).
  7. Repair short to voltage in HO2S 4 signal circuit. After repairs, go to step 9).
  8. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  9. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0152. If scan tool displays DTC P0152 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0152 FAILED THIS IGN, repair is complete.

Ensure HO2S sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S signal or ground circuits. Check for internally shorted HO2S. Check HO2S for silicone (powdery white deposit) contamination. Check for faulty PCM grounds. Perform FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

Check EVAP canister for fuel saturation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor. Check for fuel in fuel pressure regulator vacuum line.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other HO2S DTCs (except P0133, P1133, P1134, P1135, P1136, P1153, P1154, P1155, and/or P1156) are set, diagnose affected DTCs. Start engine and allow it to reach operating temperature. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0153 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0153 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  3. If scan tool also displays DTC P0153, P1133, P1134, P1135, P1136, P1153, P1154, P1155, and/or P1156 FAILED THIS IGN, go to step 8). If scan tool does not display these DTCs, go to next step.
  4. Visually inspect exhaust system for leaks near HO2S. If leaks are found, repair as necessary and return to step 2). If no leaks are found, go to next step.
  5. Visually inspect HO2S for secure installation or corrosion on terminals. Check terminal tension at HO2S and PCM. Check for damaged wiring. If a problem is found, go to step 9). If no problem is found, go to next step.
  6. Disconnect HO2S connector. Connect a jumper wire between HO2S harness connector ground circuit and chassis ground. Using scan tool, read HO2S 4 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 10).
  7. Connect a jumper wire between HO2S harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.3 volt, go to step 12). If voltage is not less than 0.3 volt, go to step 11).
  8. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After repairs, go to step 13).
  9. Repair condition as necessary. After repairs, go to step 13).
  10. Repair open HO2S ground circuit or HO2S signal circuit shorted to ground. After repairs, go to step 13).
  11. Repair open HO2S signal circuit or faulty PCM connections as necessary. After repairs, go to step 13).
  12. Replace HO2S. After replacing sensor, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0153. If scan tool displays DTC P0153 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0153 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start and warm engine to normal operating temperature. Place gear selector in Park or Neutral, and apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 4 voltage. If voltage is outside of 0.4-0.5 volt range, go to next step. If voltage is within 0.4-0.5 volt range, go to step 4)
  3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0154 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0154 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Connect a jumper wire between HO2S harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.15 volt, go to step 8). If voltage is not less than 0.15 volt, go to next step.
  5. Remove jumper wire. Using DVOM, check voltage between HO2S harness connector signal and heater ground circuits. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 7).
  6. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13). If resistance is not greater than 5 ohms, go to step 9).
  7. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13). If resistance is 5 ohms or less, go to step 10).
  8. Check for faulty connection at HO2S. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 11).
  9. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  10. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 13). If connection is okay, go to step 12).
  11. Replace HO2S. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0154. If scan tool displays DTC P0154 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0154 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check HO2S heater operation.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step. NOTE: If engine has been operating, allow engine to cool for about 30 minutes before proceeding with tests.
  2. Turn ignition on, engine off. Using scan tool, read HO2S 4 voltage. If voltage is varying from less than 0.3 volt to greater than 0.6 volt, go to DIAGNOSTIC AIDS. If voltage is within a range of 0.3-0.6 volt, go to next step.
  3. Inspect HO2S ignition feed fuse. If fuse is open, go to step 15). If fuse is okay, go to next step.
  4. Turn ignition off. Raise and support vehicle. Disconnect HO2S harness connector. Connect a test light between chassis ground and HO2S ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  5. Connect test light between HO2S harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
  6. Allow HO2S to cool for at least 10 minutes. Using DVOM, check resistance between ignition feed and heater ground circuits at HO2S. If resistance is 3-10 ohms, go to step 9). If resistance is not as specified, go to step 14).
  7. Repair open HO2S ignition feed circuit. After repairs, go to step 16).
  8. Repair open HO2S heater ground circuit. After repairs, go to step 16).
  9. Check for faulty connection at HO2S. If faulty connection is found, repair as necessary and go to step 16). If connection is okay, go to next step.
  10. Turn ignition off. Disconnect PCM connectors. Check resistance of HO2S signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary and go to step 16). If resistance is not greater than 5 ohms, go to next step.
  11. Check for faulty connection at HO2S harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  12. Check for faulty ground circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  13. Check for faulty HO2S signal circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  14. Replace HO2S. After replacing sensor, go to step 16).
  15. Locate and repair short to ground in HO2S ignition feed circuit, replace fuse. After repairs, go to next step.
  16. Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, repair is complete. If voltage is not as specified, return to step 2).

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

Circuit Description

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) FUEL TRIM values.

ST FUEL TRIM values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT FUEL TRIM values change in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim. LT and ST fuel trim can be read by using a scan tool.

Ideal FUEL TRIM value is about zero. Fuel trim value greater than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

Conditions required to set DTC are

  1. No IAC DTCs set at idle.
  2. No ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs set.
  3. No EVAP DTCs set.
  4. No misfire or injector circuit DTCs set.
  5. Engine speed 500-4000 RPM.
  6. ECT 68-230°F (20-110°C).
  7. IAT 0-104°F (-18 to 40°C).
  8. BARO greater than 10.7 psi (0.75 kg/cm 2 ).
  9. MAP 2.6-12.8 psi (0.18-0.90 kg/cm 2 )
  10. TP angle less than 90 percent.
  11. MAF 9-180 grams per second.
  12. Long term fuel trim about maximum authority (16).
  13. Short term fuel trim about maximum authority (20).
  14. Vehicle speed less than 70 MPH.
  15. Listed conditions met in FUEL TRIM CELLS 0, 1, 2, 6, and/or 7.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other DTCs (except P0171 and P0174) are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 LT and BANK 1 ST FUEL TRIM values. If BANK 1 LT FUEL TRIM value is about 16 and BANK 1 ST FUEL TRIM value is about 20, go to step 5). If values are not as specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool displays DTC P0171 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0171 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. If DTC P0174 is also present, go to next step. If DTC is not present, go to step 17).
  6. Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  7. Check PCV valve for proper installation. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  8. Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  9. Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 12).
  10. Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is greater than 5 counts, go to step 12). If value is 5 counts or less, go to next step.
  11. Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. After repairs, go to step 23) If no problem is found, go to next step.
  12. Check IAC valve for proper operation. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  13. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination and go to step 23). If fuel is okay, go to next step.
  14. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  15. Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 ST FUEL TRIM. If BANK 1 ST FUEL TRIM decreases to about zero, go to step 22). If BANK 1 ST FUEL TRIM does not decrease to about zero, go to next step.
  16. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in the «BASIC TESTING - 3.8L»(ref-20653) article. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  17. Perform EVAP SYSTEM CHECK. See FUEL EVAPORATION CONTROL, under EMISSION SYSTEMS & SUB-SYSTEMS in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  18. Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  19. Check bank 1 exhaust system for corrosion, loose or missing hardware. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  20. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, go to next step.
  21. Ensure bank 1 HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary. After repairs, go to step 23). If no problem is found, see DIAGNOSTIC AIDS.
  22. Replace MAF sensor. After replacing sensor, go to next step.
  23. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0171. If scan tool displays DTC P0171 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0171 FAILED THIS IGN, repair is complete.

Ensure HO2S wiring is routed correctly and not contacting exhaust system. Check for faulty PCM-to-engine ground connections. Check fuel pressure. Check fuel injector operation. Check for vacuum and exhaust leaks. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor.

Check for fuel contamination. See FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 1 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) FUEL TRIM values.

ST FUEL TRIM values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT FUEL TRIM values change in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim. LT and ST fuel trim can be read by using a scan tool.

Ideal FUEL TRIM value is about zero. Fuel trim value greater than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

Conditions required to set DTC are

  1. No IAC DTCs set at idle.
  2. No ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs set.
  3. No EVAP DTCs set.
  4. No misfire or injector circuit DTCs set.
  5. Engine speed 500-4000 RPM.
  6. ECT 68-230°F (20-110°C).
  7. IAT 0-104°F (-18 to 40°C).
  8. BARO greater than 10.7 psi (0.75 kg/cm 2 ).
  9. MAP 2.6-12.8 psi (0.18-0.90 kg/cm 2 )
  10. TP angle less than 90 percent.
  11. MAF 9-180 grams per second.
  12. Long term fuel trim about maximum authority (-23).
  13. Short term fuel trim about maximum authority (-11).
  14. Vehicle speed less than 70 MPH.
  15. Listed conditions met in FUEL TRIM CELLS 0, 1, 2, 6, and/or 7.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other DTCs (except P0172 and P0175) are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 LT and BANK 1 ST FUEL TRIM values. If BANK 1 LT FUEL TRIM value is about -23 and BANK 1 ST FUEL TRIM value is about -11, go to step 5). If values are not as specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0172 test runs. If scan tool displays DTC P0172 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0172 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  5. If DTC P0175 is also set, go to next step. If not, go to step 18).
  6. Check air filter element condition. Replace air filter element if necessary. After replacing filter, go to step 22). If air filter element is okay, go to next step.
  7. Check air intake duct for being collapsed or restricted. If a problem is found, repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  8. Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  9. Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 12).
  10. Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is less than 100 counts, go to step 12). If value is not less than 100 counts, go to next step.
  11. Turn ignition off. Check throttle body bore, throttle plate and IAC passages for coking and foreign objects. If a problem is found, repair as necessary. After repairs, go to step 22) If no problem is found, go to next step.
  12. Check IAC valve for proper operation. If a problem is found, repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  13. Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator and go to step 22). If no fuel is present, go to next step.
  14. Turn ignition on, engine off. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from zero percent at closed throttle to 100 percent at wide open throttle, go to next step. If TP ANGLE does not increase as specified, to step 20).
  15. Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 LT and ST FUEL TRIM. If both FUEL TRIM values decrease to about 0, go to step 21). If FUEL TRIM values do not decrease to about 0, go to next step.
  16. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in the «BASIC TESTING - 3.8L»(ref-20653) article. If a problem is found, repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  17. Perform EVAP SYSTEM CHECK. See FUEL EVAPORATION CONTROL, under EMISSION SYSTEMS & SUB-SYSTEMS in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  18. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  19. Remove HO2S 1 and HO2S 4, and check them for silicone (powdery white deposit) contamination. If HO2S is contaminated, replace HO2S and go to step 22). If HO2S is not contaminated, see DIAGNOSTIC AIDS.
  20. Check and tighten TP sensor mounting screws. If mounting screws are tight, replace TP sensor. After replacing sensor, go to step 22).
  21. Replace MAF sensor. After replacing sensor, go to next step.
  22. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0172. If scan tool displays DTC P0172 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0172 FAILED THIS IGN, repair is complete.

Check fuel pressure. Check fuel injector operation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor.

Check for faulty TP sensor operation. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 1 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. If any other DTCs (except P0171 and P0174) are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Operate vehicle in closed loop mode while using scan tool to read BANK 2 LT and ST fuel trim values. If LT fuel trim value is about 16 and ST fuel trim value is about 20, go to step 5). If values are not as specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0174 test runs. If scan tool displays DTC P0174 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0174 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  5. If DTC P0171 is also set, go to «DTC P0171»(ref-20509-S41595520412001010200000) . If DTC is not set, go to next step.
  6. Perform EVAP SYSTEM CHECK. See FUEL EVAPORATION CONTROL, under EMISSION SYSTEMS & SUB-SYSTEMS in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary and go to step 11). If no problem is found, go to next step.
  7. Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary and go to step 11). If no problem is found, go to next step.
  8. Check exhaust system for corrosion, loose or missing hardware. If a problem is found, repair as necessary and go to step 11). If no problem is found, go to next step.
  9. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary and go to step 11). If no problem is found, go to next step.
  10. Ensure HO2S 4 is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary and go to next step. If no problem is found, go to DIAGNOSTIC AIDS.
  11. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0174. If scan tool displays DTC P0174 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0174 FAILED THIS IGN, repair is complete.

Ensure HO2S wiring is routed correctly and not contacting exhaust system. Check for faulty PCM-to-engine ground connections. Check fuel pressure. Check fuel injector operation. Check for vacuum and exhaust leaks. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor.

Check for fuel contamination. See FUEL SYSTEM DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in the BASIC TESTING - 3.8L article. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 4 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other DTCs (except P0172 and P0175) are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Operate vehicle in closed loop mode while using scan tool to read LT and ST fuel trim values. If LT fuel trim value is about -23 and ST fuel trim value is about -11, go to step 5). If values are not as specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0175 test runs. If scan tool displays DTC P0175 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0175 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  5. If DTC P0172 is also set, go to «DTC P0172»(ref-20509-S14215568642001010200000) . If DTC is not set, go to next step.
  6. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary and go to step 8). If no problem is found, go to next step.
  7. Remove HO2S 4 and check for silicone (powdery white deposit) contamination. If HO2S 4 is contaminated, replace HO2S 4 and go to next step. If HO2S 4 is not contaminated, go to DIAGNOSTIC AIDS.
  8. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0172. If scan tool displays DTC P0172 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0172 FAILED THIS IGN, repair is complete.

Check fuel pressure. Check fuel injector operation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor.

Check for faulty TP sensor operation. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 4 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If DTC P1200 is also set, go to «DTC P1200»(ref-20509-S28122983642001010200000) . If DTC P1200 is not set, go to next step.
  3. Start engine and allow it to idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, go to next step. If MISFIRE CUR # is not increasing, see DIAGNOSTIC AIDS.
  4. If MISFIRE HIST # displays a very large number for more than one cylinder, go to next step. If MISFIRE HIST # does not display a very large number for more than one cylinder, go to step 14).
  5. Check vacuum hoses for splits, kinks, or improper connections. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  6. Check PCV valve for improper installation or damaged "O" rings. If a problem is found, go to step 27). If no problem is found, go to next step.
  7. Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  8. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  9. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination and go to step 27). If fuel is okay, go to next step.
  10. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  11. Disconnect MAF sensor harness connector. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, go to next step. If MISFIRE CUR # is not increasing, go to step 25).
  12. Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  13. Remove EGR valve and inspect valve, seat and passages for damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  14. Perform INJECTOR CIRCUIT TEST under FUEL SYSTEM DIAGNOSIS in the «BASIC TESTING - 3.8L»(ref-20653) article. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  15. Check ignition wire(s) associated with cylinder(s) that is misfiring. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  16. Install a spark tester on spark plug wire at spark plug end for cylinder indicating most severe misfire. Connect a jumper wire between engine ground and companion cylinder spark plug wire at spark plug end. Companion cylinders are 1 and 4, 2 and 5, and 3 and 6. Crank engine and check for crisp, Blue spark at tester. Repeat procedure for each affected cylinder. If spark is okay on all cylinders, go to step 21). If spark is not okay on any cylinder, go to next step.
  17. Remove ignition coil(s) associated with misfiring cylinder(s). Check ignition coils for cracks or carbon tracking. If a problem is found, replace damaged coil(s) and go to step 27). If no problem is found, go to next step.
  18. Check ignition coil secondary resistance. If resistance is not 5000-8000 ohms, replace ignition coil. After replacing coil, go to step 27). If resistance is as specified, go to next step.
  19. Remove ignition wire(s) associated with misfiring cylinder(s). Check ignition wire(s) boot for carbon tracking or damaged insulation. If a problem is found, replace faulty ignition wire(s). After replacing ignition wire(s), go to step 27). If no problem is found, go to next step.
  20. Check resistance of ignition wire(s) associated with misfiring cylinder(s). If resistance is greater than 30,000 ohms, replace ignition wire(s). After repairs, go to step 27). If resistance is not greater than 30,000 ohms, go to step 26).
  21. Remove spark plug(s) associated with misfiring cylinder(s). Check spark plugs for excessive fouling. If spark plugs are excessively fouled, diagnose and repair mechanical engine problem. If spark plugs are not excessively fouled, go to next step.
  22. Check spark plug insulation for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug(s). After replacing spark plug(s), go to step 27). If no problem is found, go to next step.
  23. Diagnose mechanical engine problem. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, go to next step.
  24. Check for transmission DTCs. See the TRANSMISSION SERVICING article. If a problem is found, repair as necessary. After repairs, go to step 27). If no problem is found, see DIAGNOSTIC AIDS.
  25. Replace MAF sensor. After replacing sensor, go to step 27).
  26. Replace ignition control module. After replacing module, go to next step.
  27. Using scan tool, read and record FREEZE FRAME data. Clear DTCs. Start engine and allow it to idle. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, return to step 2). If MISFIRE CUR # is not increasing, repair is complete.

Check secondary ignition wires. Check for damaged or faulty ignition coil. Substitute a known-good ignition coil. Check system grounds. Check MAF sensor, air induction system, fuel pressure, injectors, and EGR valve.

Extended idle periods or short trip driving could leave deposits on HO2S. Deposits could cause HO2S to respond slowly, affecting fuel control and causing misfire at idle.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If engine knock can be heard, repair engine mechanical problem before proceeding with test. Operate vehicle within conditions required to set DTC. Using scan tool, select DTC, SPECIFIC function and enter DTC P0325. If scan tool displays DTC P0325 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P0325 FAILED THIS IGN, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Read and record FAIL RECORDS data for DTC P0325. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0325 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0325 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Ensure KS harness is not routed too close to high-voltage wires, such as spark plug cables, ignition coils or other high-voltage components. Reroute harness if necessary. After repairs, go to step 8). If harness routing is okay, go to next step.
  5. Ensure KS module is fully seated and installed properly. If a problem is found, repair as necessary. After repairs, go to step 8). If no problem is found, go to next step.
  6. Replace KS module. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. Monitor scan tool until DTC P0325 test runs. If scan tool displays DTC P0325 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0325 FAILED THIS IGN, go to step 8).
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0325. Monitor scan tool until DTC P0325 test runs. If scan tool displays DTC P0325 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0325 FAILED THIS IGN, repair is complete.

Check for faulty connection at PCM. Check KS connector for damage. Ensure KS is installed properly.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If engine knock can be heard, repair engine mechanical problem before proceeding with test. Operate vehicle within conditions required to set DTC. Using scan tool, select DTC, SPECIFIC function and enter DTC P0326. If scan tool displays DTC P0326 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P0326 FAILED THIS IGN, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Read and record FAIL RECORDS data for DTC P0326. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0326 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0326 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect KS connector. Using a DVOM, check voltage between engine ground and terminal at each KS. If voltage is about 5 volts, go to next step. If voltage is not as specified, go to step 9).
  5. Using DVOM in 400 k/ohm scale, check resistance between engine ground and terminal at each KS. If resistance is about 100 k/ohms, go to next step. If resistance is not as specified, go to step 10).
  6. Turn ignition off. Using DVOM in 2-volt AC scale, check voltage between engine ground and bank 1 KS terminal. Start engine and allow it to idle. Repeat procedure for bank 2 KS. If any signal is present for either KS, go to step 10). If signal is not present, go to next step.
  7. With DVOM still connected between KS terminal and engine ground, tap on engine while observing DVOM. If any signal is present, go to next step. If signal is not present, go to step 10).
  8. Check KS harness connector signal circuit for incorrect routing near secondary wires or faulty terminal connection at KS. If a problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to step 11).
  9. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on and check KS signal circuit between PCM and KS harness connector for open, short to voltage or short to ground. If a problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to step 11).
  10. Replace affected KS. After replacing sensor, go to step 14).
  11. Turn ignition off. Disconnect PCM connectors. Check KS signal circuit for proper terminal connection at PCM. Repair or replace terminal as necessary. After repairs, go to step 14). If terminal is okay, go to next step.
  12. Replace KS module. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. Monitor scan tool until DTC P0326 test runs. If scan tool displays DTC P0326 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0326 FAILED THIS IGN, go to step 14).
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Read and record FAIL RECORDS data for DTC P0326. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0326 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0326 FAILED THIS IGN, repair is complete.

Check for faulty connection at PCM. Check KS and PCM connectors for damage. Ensure KS harness is not routed too close to high-voltage wires, such as spark plug cables, ignition coils or other high-voltage components. Ensure KS is installed properly.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Operate vehicle within conditions required to set DTC. Using scan tool, select DTC, SPECIFIC function and enter DTC P0327. If scan tool displays DTC P0327 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P0327 FAILED THIS IGN, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Read and record FAIL RECORDS data for DTC P0327. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0327 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0327 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Disconnect both KS connectors. Using a DVOM, check voltage between engine ground and terminal at each KS. If voltage is 5 volts for both KS, go to next step. If voltage is not as specified, go to step 9).
  5. Using DVOM in 400 k/ohm scale, check resistance between engine ground and terminal at each KS. If resistance is about 100 k/ohms for both KS, go to next step. If resistance is not as specified, go to step 10).
  6. Connect DVOM to bank 1 KS terminal and ground. Select 2-volt AC scale on DVOM. Engine idling, observe DVOM. Repeat for bank 2 KS. If voltage is indicated on DVOM for either KS, go to step 10). If not, go to next step.
  7. With DVOM still connected between KS terminal and engine ground, tap on engine while observing DVOM. If any signal is present, go to next step. If signal is not present, go to step 10).
  8. Check KS harness connector for incorrect routing or faulty terminal connection at KS. If a problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to step 11).
  9. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on and check KS signal circuit between PCM and KS harness connector for open, short to voltage or short to ground. If a problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to step 11).
  10. Replace affected KS. After replacing sensor, go to step 14).
  11. Turn ignition off. Disconnect PCM connectors. Check KS signal circuit for proper terminal connection at PCM. Repair or replace terminal as necessary. After repairs, go to step 14). If terminal is okay, go to next step.
  12. Replace KS module. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. Monitor scan tool until DTC P0327 test runs. If scan tool displays DTC P0327 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0327 FAILED THIS IGN, go to step 14).
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Read and record FAIL RECORDS data for DTC P0327. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0327 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0327 FAILED THIS IGN, repair is complete.

Check for faulty connection at PCM. Check KS and PCM connectors for damage. Ensure KS harness is not routed too close to high-voltage wires, such as spark plug cables, ignition coils or other high-voltage components. Insure KS is installed properly.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start and run, see ENGINE DOES NOT START in the «BASIC TESTING - 3.8L»(ref-20653) article.
  3. Using scan tool, clear DTC P0336. Start engine and allow to idle for one minute. Read DTCs. If DTC P0336 resets, go to next step. If DTC does not reset, go to DIAGNOSTIC AIDS.
  4. Disconnect ICM and PCM harness connectors. Check for open or short to ground in 18X reference circuit between ICM and PCM harness connectors. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to next step.
  5. Reconnect ICM connector. Using DVOM, check voltage on 18X reference circuit at PCM harness connector while cranking engine. If voltage is about 3 volts, go to step 8). If voltage is not as specified, go to next step.
  6. Check for faulty connections at ICM. If a faulty connection is found, repair as necessary. After repairs, go to step 11). If connections are okay, go to next step.
  7. Replace ICM. After replacing module, go to step 11).
  8. Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to next step.
  9. Check for faulty connections at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connections are okay, go to next step.
  10. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  11. Read and record FAIL RECORDS data for DTC P0336. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0336 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0336 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe a voltmeter connected to 18X reference circuit at PCM harness connector while moving all related harness and connectors. A change in voltage indicates fault location.

Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read and record FAIL RECORDS data for DTC P0341. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0341 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0341 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  3. Turn ignition off. Disconnect PCM connectors. Using DVOM, check voltage on CMP sensor signal circuit at PCM harness connector. Turn ignition on. If voltage is about 5 volts, go to next step. If voltage is not as specified, go to step 5).
  4. Remove CMP sensor, leaving harness connector connected. Place a magnet on sensor. If voltage is now about zero volts, go to step 16). If voltage is not as specified, go to step 8).
  5. If voltage is greater than 5 volts, go to step 7). If voltage is 5 volts or less, go to next step.
  6. Turn ignition off. Disconnect Ignition Control Module (ICM) connector. Leave PCM connector disconnected. Turn ignition on. Connect a test light between battery voltage and ICM harness connector CMP sensor signal and CMP sensor input circuits. If test light illuminates, locate and repair short to ground in CMP sensor signal or input circuit and go to step 24). If test light does not illuminate, go to step 13).
  7. Turn ignition off. Disconnect Ignition Control Module (ICM) connector. Leave PCM connector disconnected. Turn ignition on. Connect a test light between engine ground and ICM harness connector CMP sensor input circuit. If test light illuminates, locate and repair short to voltage in CMP sensor input circuit. After repairs, go to step 24). If test light does not illuminate, go to step 18).
  8. Disconnect CMP sensor. Check voltage between CMP sensor harness connector sensor feed and sensor ground circuit. If voltage is about battery voltage, go to next step. If voltage is not as specified, go to step 12).
  9. Check voltage CMP sensor harness connector sensor signal and sensor ground circuits. If voltage is 5-7 volts, go to next step. If voltage is not as specified, go to step 11).
  10. Check voltage on PCM harness connector CMP sensor input signal circuit. Connect a test light to CMP sensor harness connector sensor signal circuit. Repeatedly touch other end of test light to engine ground. If voltage switches from zero to 5 volts, go to step 15). If voltage does not switch, go to step 14).
  11. Turn ignition off. Disconnect Ignition Control Module (ICM) connector. Leave CMP sensor connector disconnected. Turn ignition on. Check CMP sensor signal circuit for open or short to voltage. Check CMP sensor input signal circuit for short to voltage. If a problem is found, repair as necessary. After repairs, go to step 24). If no problem is found, go to step 14).
  12. Turn ignition off. Disconnect ICM and CMP sensor connectors. Check sensor feed and sensor ground circuits for open between ICM and CMP sensor. If a problem is found, repair as necessary. After repairs, go to step 24). If no problem is found, go to step 14).
  13. Check for open in CMP sensor input signal circuit between ICM and PCM. If open is found, repair as necessary. After repairs, go to step 24). If open is not found, go to next step.
  14. Check for faulty connection at ICM. If faulty connection is found, repair as necessary. After repairs, go to step 24). If ICM connection is okay, go to step 17).
  15. Check for faulty connection at CMP sensor. If faulty connection is found, repair as necessary. After repairs, go to step 24). If connection is okay, go to step 19).
  16. Check for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 24). If PCM connection is okay, go to step 20).
  17. Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness. If a problem is found, repair as necessary. After repairs, go to step 24). If no problem is found, go to next step.
  18. Replace ICM. After replacing module, go to step 24).
  19. Replace CMP sensor. After replacing sensor, go to step 24).
  20. Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness. If a problem is found, repair as necessary. After repairs, go to step 24). If no problem is found, go to next step.
  21. Reinstall CMP sensor. Using DVOM, check voltage on CMP sensor input signal circuit while cranking engine. If voltage switches from zero to 4 volts, go to next step. If voltage does not switch, go to step 23).
  22. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 24).
  23. Replace faulty or missing CMP sensor. After repairs, go to next step.
  24. Read and record FAIL RECORDS data for DTC P0341. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0341 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0341 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe a voltmeter connected to CMP sensor input circuit at PCM harness connector while moving all related harness and connectors. A change in voltage indicates fault location.

Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness.

PCM tests Exhaust Gas Recirculation (EGR) valve by momentarily commanding valve on while monitoring engine MAP. PCM will illuminate MIL and store DTC P0401 if expected increase is not seen under certain conditions during deceleration.

Conditions required to set DTC are

  1. No ECT, IAT, MAP, or TP sensor DTCs set.
  2. No misfire, linear EGR (pintle position) or vehicle speed sensor DTCs set.
  3. BARO is greater than 10 psi (0.7 kg/cm 2 ).
  4. ECT greater than 180°F (80°C).
  5. Vehicle speed greater than 25 MPH.
  6. Engine speed is 800-1400 RPM.
  7. IAC position steady.
  8. TP angle less than one percent.
  9. Commanded state of A/C relay is steady.
  10. MAP changes monitored during EGR flow test indicate insufficient EGR flow.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Inspect exhaust system for modifications or leaks. If a problem is found, repair as necessary. After repairs, go to step 5). If no problem is found, go to next step.
  3. Remove EGR valve and check pintle, valve and passages and adapter for excessive deposits or restriction. Check EGR valve gasket and pipes for leaks. If a problem is found, repair as necessary. After repairs, go to step 5). If no problem is found, go to next step.
  4. Remove EGR inlet and outlet pipes from exhaust and intake manifolds. Inspect manifold EGR ports and pipes for blockage or damage. If a problem is found, repair as necessary. After repairs, go to next step. If no problem is found, see DIAGNOSTIC AIDS.
  5. Read and record FAIL RECORDS data for DTC P0401. Clear DTCs and monitor EGR TEST COUNT while operating vehicle within conditions noted in DIAGNOSTIC AIDS until 9-12 test counts have been taken. Read SPECIFIC DTC. If scan tool displays DTC P0401 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0401 TEST RAN AND PASSED, return to step 2).

PCM will only run EGR flow test during gradual deceleration, a closed throttle condition and with vehicle speed greater than 25 MPH. Accelerate vehicle to greater than 25 MPH, and gradually decelerate 9-12 times.

Check for faulty connections or damaged harness. Inspect PCM harness connector EGR control circuit for backed-out terminal. Observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

If EGR valve shows signs of excessive heat, check exhaust system for blockage or plugged catalytic converter.

Three-Way Catalyst (TWC) system is used to control emission. PCM uses signal from Heated Oxygen Sensors (HO2S) to read efficiency of TWC. PCM will set DTC P0420 if TWC oxygen storage capacity is less than a predetermined threshold.

Conditions required to set DTC are

  1. IAT greater than 32°F (0°C).
  2. ECT greater than 167°F (75°C).
  3. MAF 15-32 gm/sec.
  4. Engine load less than 63 percent and steady.
  5. Engine speed less than 4000 RPM.
  6. Conditions are present for up to 4 minutes.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Diagnose any other DTCs present before proceeding. If no other DTCs are present, go to next step.
  3. Ensure TWC is an original equipment part. Check TWC for dents or discoloration caused by excessive heat. Ensure no internal damaged catalyst rattle exists. If a problem is found, repair as necessary. After repairs, go to step 6). If no problems are found, go to next step.
  4. Check exhaust system for leaks, damage, loose or missing hardware. If a problem is found, repair as necessary. After repairs, go to step 7). If no problems are found, go to next step.
  5. Ensure HO2S 2 is securely installed and that harness is not damaged or contacting exhaust. If a problem is found, repair as necessary. After repairs, go to step 7). If no problems are found, go to next step.
  6. Replace TWC. Check for possible engine misfire DTC or engine mechanical problem, and go to next step.
  7. Read and record FAIL RECORDS data for DTC P0401. Clear DTCs. Start engine and allow it to reach 167F (75C). Run engine while monitoring scan tool IAC RPM control function to maintain MAF at 12-15 grams per second for at least 2 minutes. Using scan tool, monitor TWC MONITOR TEST COUNTER while operating vehicle within conditions required to set DTC. Continue operating vehicle until TWC MONITOR TEST COUNTER reaches 49 and returns to zero 2 times. Read SPECIFIC DTC. If scan tool displays DTC P0420 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0420 TEST RAN AND PASSED, return to step 2).

Check for faulty connections or damaged harness. Inspect PCM harness connector EGR control circuit for backed-out terminal. Observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

Ensure engine has reached operating temperature. Place gear selector in Park. Using scan tool, monitor HO2S 1 and HO2S 2 values while using scan tool IAC RPM function to maintain MAF at 10 grams per second. Compare activity between HO2S 1 and HO2S 2 for 30 seconds. If activity between both HO2S is about equal, a problem exists. Repeat DTC P0420.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn engine on and allow it to idle. Using scan tool, command EVAP purge solenoid on, while monitoring EVAP VACUUM SW on ENG 2 data list. If scan tool displays PURGE, go to next step. If scan tool does not display PURGE, go to step 4).
  3. Turn ignition on, engine off. Using scan tool, read and record FAIL RECORDS data for DTC P0441. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0441 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0441 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Plug vacuum line between EVAP purge canister and EVAP vacuum switch. Turn engine on and allow it to idle. Using scan tool, command EVAP purge solenoid on, while monitoring EVAP VACUUM SW on ENG 2 data list. If scan tool displays PURGE, go to next step. If scan tool does not display PURGE, go to step 6).
  5. Check vacuum line to canister for damage or improper connections. If a problem is found, repair as necessary. After repairs, go to step 20). If no problem is found, go to step 14).
  6. Turn ignition off. Connect a vacuum gauge between EVAP purge solenoid and vacuum switch. Start engine and allow it to idle. Using scan tool, command EVAP purge solenoid on. If vacuum gauge reads 12 in. Hg, go to next step. If vacuum is not as specified, go to step 8).
  7. Turn ignition off. Disconnect vacuum switch harness connector. turn ignition on. Observe EVAP VACUUM SW. If scan tool displays PURGE, go to step 15). If scan tool does not display PURGE, go to step 9).
  8. Turn ignition off. Connect a vacuum gauge to EVAP purge solenoid vacuum source. Start engine and allow it to idle. If vacuum gauge reads 12 in. Hg, go to step 10). If vacuum is not as specified, go to step 16).
  9. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Check for short to voltage in EVAP vacuum switch input circuit. If a problem is found, repair as necessary. After repairs, go to step 20). If no problem is found, go to step 19).
  10. Turn ignition off. Disconnect EVAP purge solenoid harness connector. Connect a test light across EVAP purge solenoid harness connector signal and ground circuits. Turn ignition on. Using scan tool, command EVAP solenoid on. If test light illuminates, go to step 17). If test light does not illuminate, go to next step.
  11. Turn ignition off. Disconnect PCM connectors. Connect a test light across EVAP purge solenoid harness connector signal and ground circuits. Turn ignition on. Connect a jumper wire between EVAP purge solenoid harness connector driver circuit and PCM harness connector ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
  12. Check for faulty connection at PCM. If connection is faulty, repair as necessary. After repairs, go to step 20). If connection is okay, go to step 19).
  13. Repair EVAP purge solenoid ignition feed circuit for open or short to ground, or EVAP purge solenoid driver circuit for open. After repairs, go to step 20).
  14. Replace EVAP canister. After replacing canister, go to step 20).
  15. Replace EVAP vacuum switch. After replacing switch, go to step 20).
  16. Locate and repair cause of no vacuum. After repairs, go to step 20).
  17. Check for faulty connection at EVAP purge solenoid. If faulty connection is found, repair as necessary. After repairs, go to step 20). If connection is okay, go to next step.
  18. Replace EVAP purge solenoid. After replacing EVAP solenoid, go to step 20).
  19. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  20. Read and record FAIL RECORDS data for DTC P0441. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0441 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0441 FAILED THIS IGN, repair is complete.

Check vacuum canister and hoses for damage. Check for faulty connections or damaged harness. Observe scan tool EVAP VACUUM SW display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Retrieve and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition off. Raise and support vehicle. Start engine and idle in gear. Using scan tool, read VSS SIGNAL. If scan tool displays greater than zero MPH, see DIAGNOSTIC AIDS. If scan tool displays zero MPH, go to next step.
  3. With engine still idling in gear, observe speedometer. If speedometer displays greater than zero MPH, go to step 7). If speedometer displays zero MPH, go to next step.
  4. Turn ignition off. Connect Signal Generator (J33431-B) to VSS harness connector. Turn ignition on. Turn signal generator on. If scan tool displays greater than zero MPH, go to step 6). If scan tool does not display zero MPH, go to next step.
  5. Turn ignition off. Disconnect PCM harness connectors. Check VSS harness connector signal and ground circuits for open or shorts. If a problem is found, repair as necessary. After repairs, go to step 8). If no problem is found, go to step 7).
  6. Replace VSS. After replacing sensor, go to step 8)
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Turn ignition off. Raise and support vehicle. Start engine and idle in gear. Using scan tool, read VSS SIGNAL. If scan tool displays greater than zero MPH, repair is complete. If scan tool displays zero MPH, return to step 3).

Check for faulty connection at VSS and PCM connectors. Check for damaged harness. Check for loose or damaged VSS rotor.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read DTCs. If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. If ENGINE SPEED remains within 100 RPM of desired RPM for each command, see DIAGNOSTIC AIDS. If ENGINE SPEED is not as specified, to next step.
  4. Disconnect IAC harness connector. Install IAC Node Light (J37027) in IAC harness connector. Monitor node lights while commanding engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. Both node lights should cycle Green and Red, but not off as RPM changes from 500-1500 RPM. If lights flash as specified, go to step 6). If lights do not flash as specified, go to next step.
  5. Check IAC "A" high and low, and "B" high and low circuits for open, short to voltage or short to ground. If a problem is found, repair as necessary. After repairs, go to step 11). If circuits are okay, go to step 9).
  6. Ensure throttle stop screw has not been tampered with. Check for stuck IAC valve or throttle linkage. Check for restrictions, collapse or blockage in air intake system, air ducts or air filter. Check throttle body bore and IAC for excessive deposits. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to next step.
  7. Check for faulty connection at IAC harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to next step.
  8. Replace IAC valve. After replacing IAC valve, go to step 11).
  9. Check for faulty connection at PCM harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to next step.
  10. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  11. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. If ENGINE SPEED remains within 100 RPM of desired RPM for each command, repair is complete. If ENGINE SPEED is not as specified, return to step 2).

Check for faulty connection at IAC and PCM connectors. Check for damaged harness. Check for restrictions, collapse or blockage in air intake system, air ducts or air filter. Check throttle body bore and IAC for excessive deposits. Check for large vacuum leak, such as incorrectly installed PCV valve or disconnected brake booster hose. Check for restricted air intake system.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read DTCs. If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. If ENGINE SPEED remains within 100 RPM of desired RPM for each command, see DIAGNOSTIC AIDS. If ENGINE SPEED is not as specified, to next step.
  4. Disconnect IAC harness connector. Install IAC Node Light (J 37027) in IAC harness connector. Monitor node lights while commanding engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. Both node lights should cycle Green and Red, but not OFF as RPM changes from 500-1500 RPM. If lights flash as specified, go to step 6). If lights do not flash as specified, go to next step.
  5. Check IAC "A" high and low, and "B" high and low circuits for open, short to voltage or short to ground. If a problem is found, repair as necessary. After repairs, go to step 11). If circuits are okay, go to step 9).
  6. Check for vacuum leaks. Ensure throttle stop screw has not been tampered with. Check for throttle plate or shaft binding. Check accelerator and speed control cables for misadjustment or binding. Check for faulty, missing or incorrectly installed PCV valve. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to next step.
  7. Check for faulty connection at IAC harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to next step.
  8. Replace IAC valve. After replacing IAC valve, go to step 11).
  9. Check for faulty connection at PCM harness connector. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to next step.
  10. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  11. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. If ENGINE SPEED remains within 100 RPM of desired RPM for each command, repair is complete. If ENGINE SPEED is not as specified, return to step 2).

Check for faulty connection at IAC and PCM connectors. Check for damaged harness. Check for vacuum leaks. Check throttle body bore and IAC for excessive deposits. Check throttle plate for sticking.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, read A/C refrigerant pressure sensor voltage. If voltage is less than 0.1 volt, go to step 5). If voltage is not less than 0.1 volt, go to next step.
  3. If voltage is greater than 4.8 volts, go to next step. If voltage is not greater than 4.8 volts, go to DIAGNOSTIC AIDS.
  4. While observing scan tool, disconnect A/C refrigerant pressure sensor connector. If voltage is about zero volts, go to step 12). If voltage is not as specified, go to step 11).
  5. Disconnect A/C refrigerant pressure sensor connector. Connect a fused jumper wire between A/C refrigerant pressure sensor harness connector 5-volt reference and signal circuit. If voltage is about 5 volts, go to step 16). If voltage is not as specified, go to next step.
  6. Using a DVOM, check voltage between A/C pressure sensor harness connector 5-volt reference and ground circuits. If voltage is about 5 volts, go to step 9). If voltage is not as specified, go to next step.
  7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 17). If connection is okay, go to next step.
  8. Check for open or a faulty splice in 5-volt reference circuit. If problem is found, go to step 18). If no problem is found, go to step 13).
  9. Check A/C refrigerant signal circuit for faulty connection at PCM. If faulty connection is found, go to step 17). If connection is okay, go to next step.
  10. Check A/C refrigerant pressure signal circuit between A/C refrigerant pressure sensor connector and PCM for open or short to ground. If problem is found, go to step 18). If no problem is found, go to step 20)
  11. Check A/C refrigerant pressure signal circuit between A/C refrigerant pressure sensor connector and PCM for short to voltage. If problem is found, go to step 18). If no problem is found, go to step 20)
  12. Check 5-volt reference circuit for short to voltage. If problem is found, repair as necessary. After repairs, go to step 18). If no problem is found, go to next step.
  13. Check for faulty sensor ground circuit terminal connection at PCM. If faulty connection is found, go to step 17). If connection is okay, go to next step.
  14. Check for faulty sensor ground circuit terminal connection at A/C refrigerant pressure sensor connector. If faulty connection is found, go to step 17). If connection is okay, go to next step.
  15. Check for open or faulty splice in sensor ground circuit. If a problem is found, go to step 18). If no problem is found, go to step 19).
  16. Check for faulty 5-volt reference or A/C refrigerant pressure signal circuit terminal connection at A/C refrigerant pressure sensor. If faulty connection is found, go to next step. If connections are okay, go to step 19).
  17. Replace faulty harness connector terminal. After repairs, go to step 21).
  18. Locate and repair open/short circuit in wiring harness as necessary. After repairs, go to step 21).
  19. Replace A/C refrigerant pressure sensor. After replacing sensor, go to step 21).
  20. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  21. Using scan tool, clear DTCs. Read A/C refrigerant pressure sensor voltage. If voltage is 0.1-4.8 volts, repair is complete. If voltage is not as specified, return to step 2).

Check for faulty connections or damaged harness. Observe scan tool A/C refrigerant pressure sensor display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If DTC P1635 is also set, diagnose DTC P1635 before proceeding. If DTC is not set, go to next step.
  3. Start and run engine at greater than 1000 RPM. Using scan tool, observe IGNITION 1 voltage on ENG. 2 DATA LIST. If voltage is 10-16 volts, go to step 5). If voltage is not as specified, go to next step.
  4. Read and record FAIL RECORDS data for DTC P0560. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0560 test runs. If scan tool displays DTC P0560 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0560 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Install DVOM between battery terminals. Monitor DVOM while running engine at greater than 1000 RPM. If voltage is 10-16 volts, go to next step. If voltage is not as specified, go to step 7).
  6. Turn headlights on and place A/C switch on high. Monitor DVOM while running engine at greater than 2000 RPM. If voltage is 10-16 volts, go to step 8). If voltage is not as specified, go to next step.
  7. Turn ignition off. Disconnect generator electrical connector. Turn ignition on. Connect DVOM between generator harness connector control circuit and engine ground. Using scan tool, command GEN L TERM on. If voltage is 10-16 volts, go to step 12). If voltage is not as specified, go to step 10).
  8. Compare IGNITION 1 voltage display on scan tool with DVOM voltage reading. If both values are close, see DIAGNOSTIC AIDS. If both values are not close, go to next step.
  9. Check PCM ignition feed circuit for poor connection between ignition switch and PCM. If problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to step 13).
  10. Check generator control circuit for open or short to ground between generator and PCM. If problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to next step.
  11. Check generator control circuit for faulty connection at PCM. If problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, go to step 13).
  12. Check generator control circuit for faulty connection at generator. If problem is found, repair as necessary. After repairs, go to step 14). If no problem is found, see DIAGNOSTIC AIDS.
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Clear DTCs. Start and run engine at greater than 1000 RPM. Using scan tool, observe IGNITION 1 voltage on ENG. 2 DATA LIST. If voltage is 10-16 volts, repair is complete. If voltage is not as specified, return to step 2).

Check for faulty connections or damaged harness. Observe scan tool IGNITION 1 voltage display while moving all related harness and connectors. A change in scan tool display indicates fault location.

PCM uses an Electrically Erasable Programmable Read Only Memory (EEPROM). EEPROM contains program information and calibrations required for engine, transaxle, and powertrain diagnostics operation.

Condition required to set DTC is

  1. PCM detects an internal program fault (check sum error).
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, repeat OBD system check.

Only possible repair is replacement and programming of PCM.

PCM uses an Electrically Erasable Programmable Read Only Memory (EEPROM). EEPROM contains program information and calibrations required for engine, transaxle, and powertrain diagnostics operation.

Condition required to set DTC is

  1. PCM does not contain correct program(s) required to operate vehicle.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using special equipment, program PCM with correct software. Using scan tool, retest for DTC P0602. If DTC P0602 sets, go to next step. If DTC does not set, repair is complete.
  3. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, repeat OBD system check.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on, engine off. Using scan tool, observe CLUTCH PEDAL SWITCH state. If scan tool displays RELEASED, go to next step. If scan tool does not display RELEASED, go to step 6).
  3. Depress clutch pedal. If scan tool displays APPLIED, go to DIAGNOSTIC AIDS. If scan tool does not display APPLIED, go to next step.
  4. Disconnect CA switch harness connector. If scan tool displays APPLIED, go to step 13). If scan tool does not display APPLIED, go to next step.
  5. Turn ignition off. Disconnect PCM. Connect a test light between battery voltage and PCM harness connector CA switch input circuit. If test light illuminates, go to step 9). If test light does not illuminate, go to step 15).
  6. Disconnect clutch pedal switch connector. Connect test light between battery voltage and CA switch harness connector ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
  7. Connect a fused jumper wire between CA switch harness connector input and ground circuits. If scan tool displays RELEASED, go to step 11). If not, go to next step.
  8. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Check clutch input circuit for open or short to voltage between PCM and CA switch. If a problem is found, repair as necessary. After repairs, go to step 16). If no problem is found, go to step 14).
  9. Locate and repair short to ground in clutch pedal input circuit. After repairs, go to step 16).
  10. Locate and repair open in CA switch ground circuit. After repairs, go to step 16).
  11. Check CA switch adjustment. If a problem is found, adjust CA switch and go to step 16). If no problem is found, go to next step.
  12. Check for faulty connection and CA switch. If a faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  13. Replace clutch pedal switch. After replacing switch, go to step 16).
  14. Check for faulty connection at PCM. If a faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to next step.
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  16. Turn ignition on, engine off. Using scan tool, observe CLUTCH PEDAL SWITCH state. If scan tool displays RELEASED, go to next step. If scan tool does not display RELEASED, return to step 6).
  17. Depress clutch pedal. If scan tool displays APPLIED, repair is complete. If scan tool does not display APPLIED, return to step 4).

Check for faulty connections or damaged harness. Observe scan tool CA switch display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0108 is also set, diagnose DTC P0108 before proceeding. If DTC is not set, go to next step.
  3. If DTC P1111, P1115, and/or P1121 is also set, go to step 6). If none of these DTCs are set, go to next step.
  4. Check for faulty sensor ground circuit terminal at MAP sensor. If problem is found, go to step 9). If no problem is found, go to next step.
  5. Check MAP signal circuit between MAP sensor harness connector and PCM for intermittent short to voltage. If a problem is found, go to step 10). If no problem is found, go to step 8).
  6. Check for intermittent short to voltage on 5-volt reference circuit between PCM and MAP, EGR and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
  7. Check for faulty ground circuit terminal connection at PCM. If problem is found, go to step 9). If no problem is found, go to next step.
  8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, see DIAGNOSTIC AIDS.
  9. Replace faulty connector terminal. After repairs, go to step 11).
  10. Locate and repair intermittent open/short circuit. After repairs, go to next step.
  11. Read and record FAIL RECORDS data for DTC P1106. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1106 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1106 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool MAP display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0107 is also set, diagnose DTC P0107 before proceeding. If DTC is not set, go to next step.
  3. If DTC P1122 is also set, go to step 6). If DTC is not set, go to next step.
  4. Check for faulty 5-volt reference or signal circuit connection at MAP sensor. If a problem is found, go to step 9). If no problem is found, go to next step.
  5. Check signal circuit between MAP sensor and PCM for intermittent open or short to ground. If problem is found, go to step 10). If no problem is found, go to step 8).
  6. Check for intermittent short to ground on 5-volt reference circuit between PCM and EGR valve, MAP and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
  7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 9). If connection is okay, go to next step.
  8. Check for intermittent open or faulty splice in 5-volt reference circuit. If a problem is found, go to step 10). If no problem is found, see DIAGNOSTIC AIDS.
  9. Replace faulty connector terminal(s). After replacing terminals, go to step 11).
  10. Repair circuit as necessary. After repairs, go to next step.
  11. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1107. If scan tool displays DTC P1107 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1107 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool MAP display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0113 is also set, diagnose DTC P0113 before proceeding. If DTC is not set, go to next step.
  3. If DTC P1106, P1115, and/or P1121 is also set, go to step 6). If none of these DTCs are set, go to next step.
  4. Check for faulty sensor ground circuit terminal at IAT sensor. If problem is found, repair as necessary. After repairs, go to step 10). If no problem is found, go to next step.
  5. Check for faulty signal circuit connection at IAT sensor. If faulty connection is found, repair as necessary. After repairs, go to step 10). If connection is okay, go to next step.
  6. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent open. If open is found, repair as necessary. After repairs, go to step 10). If no open is found, go to next step.
  7. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 10). If no short to voltage is found, go to next step.
  8. Check for faulty ground circuit terminal connection at PCM. If problem is found, repair as necessary. After repairs, go to step 10). If no problem is found, go to next step.
  9. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, repair as necessary. After repairs, go to next step. If circuit is okay, see DIAGNOSTIC AIDS.
  10. Read and record FAIL RECORDS data for DTC P1111. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1111 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1111 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool IAT display while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed IAT sensor. See IAT TEMPERATURE-TO-RESISTANCE VALUES.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0112 is also set, diagnose DTC P0112 before proceeding. If DTC is not set, go to next step.
  3. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent short to ground. If short to ground is found, repair as necessary. After repairs, go to next step. If no short to ground is found, see DIAGNOSTIC AIDS.
  4. Read and record FAIL RECORDS data for DTC P1112. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1112 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1112 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool IAT display while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed IAT sensor.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0117 is also set, diagnose DTC P0117 before proceeding. If DTC is not set, go to next step.
  3. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent short to ground. If short to ground is found, repair as necessary. After repairs, go to next step. If no short to ground is found, see DIAGNOSTIC AIDS.
  4. Read and record FAIL RECORDS data for DTC P1114. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1114 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1114 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool IAT display while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor. See ECT TEMPERATURE-TO-RESISTANCE VALUES table.

Temperature °F (°C)Ohms
212 (100)177
194 (90)241
158 (70)467
122 (50)973
104 (40)1459
86 (30)2238
68 (20)3520
50 (10)5670

ECT TEMPERATURE-TO-RESISTANCE VALUES

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0118 is also set, diagnose DTC P0118 before proceeding. If DTC is not set, go to next step.
  3. If DTC P1106, P1111, and/or P1121 is also set, go to step 8). If these DTCs are not set, go to next step.
  4. Check for faulty sensor ground circuit terminal at ECT sensor. If problem is found, repair as necessary. After repairs, go to step 10). If no problem is found, go to next step.
  5. Check for faulty signal circuit connection at ECT sensor. If faulty connection is found, repair as necessary. After repairs, go to step 10). If connection is okay, go to next step.
  6. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent open. If open is found, repair as necessary. After repairs, go to step 10). If no open is found, go to next step.
  7. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 10). If no short to voltage is found, go to next step.
  8. Check for faulty ground circuit terminal connection at PCM. If problem is found, repair as necessary. After repairs, go to step 10). If no problem is found, go to next step.
  9. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, repair as necessary. After repairs, go to next step. If no problem is found, see DIAGNOSTIC AIDS.
  10. Read and record FAIL RECORDS data for DTC P1115. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1115 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1115 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool ECT display while moving all related harness and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor. See ECT TEMPERATURE-TO-RESISTANCE VALUES .

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0123 is also set, diagnose DTC P0123 before proceeding. If DTC is not set, go to next step.
  3. If DTC P1106, P1111, and/or P1115 is also set, go to step 6). If none of these DTCs are set, go to next step.
  4. Check for faulty sensor ground circuit terminal at TP sensor. If problem is found, go to step 9). If no problem is found, go to next step.
  5. Check TP signal circuit between TP sensor harness connector and PCM for intermittent short to voltage. If a problem is found, go to step 10). If no problem is found, go to step 8).
  6. Check for intermittent short to voltage on 5-volt reference circuit between PCM and MAP, EGR and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
  7. Check for faulty ground circuit terminal connection at PCM. If problem is found, go to step 9). If no problem is found, go to next step.
  8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, see DIAGNOSTIC AIDS.
  9. Replace faulty connector terminal. After repairs, go to step 11).
  10. Locate and repair intermittent open/short circuit and go to next step.
  11. Read and record FAIL RECORDS data for DTC P1121. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1121 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1121 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool TP display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If DTC P0122 is also set, diagnose DTC P0122 before proceeding. If DTC is not set, go to next step.
  3. If DTC P1107 is also set, go to step 6). If DTC is not set, go to next step.
  4. Check for faulty 5-volt reference or signal circuit connection at TP sensor. If a problem is found, go to step 9). If no problem is found, go to next step.
  5. Check signal circuit between TP sensor and PCM for intermittent open or short to ground. If problem is found, go to step 10). If no problem is found, go to step 8).
  6. Check for intermittent short to ground on 5-volt reference circuit between PCM and EGR valve, MAP and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
  7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 9). If connection is okay, go to next step.
  8. Check for intermittent open or faulty splice in 5-volt reference circuit. If a problem is found, go to step 10). If no problem is found, see DIAGNOSTIC AIDS.
  9. Replace faulty connector terminal(s). After repairs, go to step 11).
  10. Repair circuit as necessary. After repairs, go to next step.
  11. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1122. If scan tool displays DTC P1122 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1122 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool TP display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If any DTC other than P1133 or P1134 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1133 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  3. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. After repairs, go to step 11). If no exhaust leak is found, go to next step.
  4. Visually inspect HO2S 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S 1 and PCM. Check for damaged wiring. If a problem is found, go to step 8). If no problem is found, go to next step.
  5. Disconnect HO2S 1 harness connector. Connect a jumper wire between HO2S 1 harness connector ground circuit and chassis ground. Using scan tool, read HO2S 1 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 9).
  6. Connect a jumper wire between HO2S 1 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.3 volt, go to next step. If voltage is not less than 0.3 volt, go to step 10).
  7. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After repairs, go to step 11).
  8. Repair condition as necessary. After repairs, go to step 11).
  9. Repair open HO2S 1 ground circuit or HO2S 1 signal circuit shorted to ground. After repairs, go to step 11).
  10. Repair open HO2S 1 signal circuit or faulty PCM connections as necessary. After repairs, go to step 11).
  11. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1133. If scan tool displays DTC P1133 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1133 FAILED THIS IGN, repair is complete.

Check HO2S 1 heater operation. If HO2S 1 heater operation is okay, replace HO2S 1.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, select LAST TST FAIL. Record any other failed DTCs. If any DTC other than P1133 or P1134 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1133 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  3. Check if DTC P1153, P1154, P1155 and/or P1156 failed. If any of these DTCs are present, go to step 8). If not, go to next step.
  4. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. After repairs, repeat step 2). If no exhaust leak is found, go to next step.
  5. Visually inspect HO2S 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S 1 and PCM. Check for damaged wiring. If a problem is found, go to step 9). If no problem is found, go to next step.
  6. Disconnect HO2S 1 connector. Connect a jumper wire between HO2S 1 harness connector ground circuit and chassis ground. Using scan tool, read HO2S 1 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 10).
  7. Connect a jumper wire between HO2S 1 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.3 volt, go to next step. If voltage is not less than 0.3 volt, go to step 11).
  8. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After repairs, go to step 13).
  9. Repair condition as necessary. After repairs, go to step 13).
  10. Repair open HO2S 1 ground circuit or HO2S 1 signal circuit shorted to ground. After repairs, and go to step 13).
  11. Repair open HO2S 1 signal circuit or faulty PCM connections as necessary. After repairs, and go to step 13).
  12. Replace Bank 1 HO2S 1. After replacing sensor, go to next step.
  13. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1133. If scan tool displays DTC P1133 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1133 FAILED THIS IGN, repair is complete.

Check HO2S 1 heater operation. If HO2S 1 heater operation is okay, replace HO2S 1.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other DTC sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1153 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1153 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  3. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. After repairs, go to step 11). If no exhaust leak is found, go to next step.
  4. Visually inspect HO2S 4 for secure installation or corrosion on terminals. Check terminal tension at HO2S 4 and PCM. Check for damaged wiring. If a problem is found, go to step 7). If no problem is found, go to next step.
  5. Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. Using scan tool, read HO2S 2 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 8).
  6. Connect a jumper wire between HO2S 2 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.2 volt, go to step 10). If voltage is not less than 0.2 volt, go to step 9).
  7. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S and go to step 11).
  8. Repair open HO2S 2 ground circuit or HO2S 2 signal circuit shorted to ground. After repairs, go to step 11).
  9. Repair open HO2S 2 signal circuit or faulty PCM connections as necessary. After repairs, go to step 11).
  10. Replace HO2S 2. After replacing sensor, go to next step.
  11. Using scan tool, clear DTCs. Operate vehicle within conditions required to set DTC. Using scan tool, select SPECIFIC DTC INFO for DTC P1153. If scan tool displays DTC P1153 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1153 FAILED THIS IGN, repair is complete.

Check HO2S 4 heater operation. If HO2S 2 heater operation is okay, replace HO2S 2.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If any other DTC sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1154 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1154 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  3. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. After repairs, go to step 11). If no exhaust leak is found, go to next step.
  4. Visually inspect HO2S 2 for secure installation or corrosion on terminals. Check terminal tension at HO2S 2 and PCM. Check for damaged wiring. If a problem is found, go to step 7). If no problem is found, go to next step.
  5. Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. Using scan tool, read HO2S 2 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 8).
  6. Connect a jumper wire between HO2S 2 harness connector signal and ground circuits, and chassis ground. If voltage is less than 0.2 volt, go to step 10). If voltage is 0.2 volt or greater, go to step 9).
  7. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After replacing sensor, go to step 13).
  8. Repair open HO2S 2 ground circuit or HO2S 4 signal circuit shorted to ground. After repairs, go to step 11).
  9. Repair open HO2S 2 signal circuit or faulty PCM connections as necessary. After repairs, go to step 11).
  10. Replace HO2S 2. After replacing sensor, go to next step.
  11. Using scan tool, clear DTCs. Operate vehicle within conditions required to set DTC. Using scan tool, select SPECIFIC DTC INFO for DTC P1154. If scan tool displays DTC P1154 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1154 FAILED THIS IGN, repair is complete.

Check HO2S 2 heater operation. If HO2S 4 heater operation is okay, replace HO2S 4.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to idle. Using scan tool, select SPECIFIC DTC INFO for DTC P1200. If scan tool displays DTC P1200 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P1200 FAILED THIS IGN, go to next step.
  3. Turn ignition on, with engine off. Read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1200. If scan tool displays DTC P1200 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1200 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between each injector driver circuit and engine ground. If voltage is 9-16 volts on each circuit, go to next step. If voltage is not as specified on any circuit, go to step 9).
  5. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If injectors are okay, go to next step. If an injector problem is found, go to step 17).
  6. Turn ignition off. Disconnect all injector connectors. Turn ignition on. Using DVOM, check voltage between each injector driver circuit at PCM harness connector and engine ground. If voltage is zero volts on each circuit, go to next step. If voltage is not as specified, go to step 16).
  7. Check harness ignition feed circuits between injector fuse and injectors for intermittent open. Check injector driver circuits between PCM and injectors for intermittent open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 19). If no problem is found, go to next step.
  8. Check for faulty connection at injector connectors. Check injector driver circuits for faulty connection at PCM connectors. If a problem is found, go to step 19). If no problem is found, go to step 18).
  9. Turn ignition off. Disconnect affected injector connector(s). Turn ignition on. Check voltage between ignition feed circuit at affected injector connector(s) and engine ground. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 14).
  10. Connect a test light between affected injector connector(s) and battery voltage. If test light illuminates, go to step 15). If test light does not illuminate, go to next step.
  11. Turn ignition off. Connect a fused jumper cable between affected injector connector(s) ignition feed and driver circuits. Turn ignition on. Connect test light between affected injector(s) driver circuit at PCM and engine ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
  12. Check for faulty connection at injector connector(s). If faulty connection is found, repair as necessary. After repairs, go to step 19). If connection(s) are okay, go to step 17).
  13. Locate and repair open in affected injector driver circuit(s). After repairs, go to step 19).
  14. Locate and repair open or short to ground in affected ignition feed circuit(s). After repairs, go to step 19).
  15. Locate and repair short to ground in affected injector driver circuit(s). After repairs, go to step 19).
  16. Locate and repair short to voltage in affected injector driver circuit(s). After repairs, go to step 19).
  17. Replace faulty injector(s). After replacing injector(s), go to step 19).
  18. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  19. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1200. If scan tool displays DTC P1200 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1200 FAILED THIS IGN, repair is complete.

If DTC P0300 is also set, start engine and allow it to idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. An increasing MISFIRE CUR # (indicating a misfire currently occurring) for any cylinder indicates location of faulty circuit or injector.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. After performing OBD system check, go to next step.
  2. Perform crankshaft position system variation learn position.

The crankshaft position system variation compensating values are stored in the PCM's non-volatile memory after a learn procedure has been performed. If actual crankshaft position variation is not within the crankshaft position system variation compensating values stored in the PCM, DTC P0300 may set.

If the crankshaft position system variation learn procedure cannot be performed successfully, check the following conditions and correct as necessary

  1. ECT less than 158°F (70°C).
  2. Allow engine to warm-up to greater than 158°F (70°C).
  3. PCM related DTC(s) set.
  4. Scan tool crankshaft position system variation learn function will be disabled of any PCM DTCs other than DTC P1336 are stored.
  5. Camshaft position signal problem detected.
  6. 3X reference signal problem detected.
  7. 18X reference signal problem detected.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, clear DTCs. Start engine and allow it to idle for 2 minutes. Read DTCs. If DTC P1350 sets, go to next step. If DTC does not set, see DIAGNOSTIC AIDS.
  3. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check resistance between PCM harness connector IC and ground circuits. If resistance is less than 500 ohms, go to step 6). If resistance is not less than specified, go to next step.
  4. Turn ignition off. Disconnect ICM connector. Check IC circuit for open. If open is found, repair as necessary. After repairs, go to step 10). If no open is found, go to next step.
  5. Check for faulty IC circuit connection at ICM. If faulty connection is found, repair as necessary. After repairs, go to step 10). If connection is okay, go to step 8).
  6. Check for faulty IC circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 10). If connection is okay, go to next step.
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 10).
  8. Turn ignition on. Check by-pass circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 10). If short to voltage is not found, go to next step.
  9. Replace ICM. After replacing module, go to next step.
  10. Read and record FAIL RECORDS data for DTC P1350. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1350 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1350 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect ICM. Connect a DVOM between ICM harness connector IC circuit and battery voltage. With ignition on, observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Using scan tool, clear DTCs. Start engine and allow it to idle for 2 minutes. Read DTCs. If DTC P1361 sets, go to next step. If DTC does not set, see DIAGNOSTIC AIDS.
  3. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Connect a test light between battery voltage and PCM harness connector by-pass circuit. If test light illuminates, go to step 8). If test light does not illuminate, go to next step.
  4. Turn ignition on. with test light still connected between battery voltage and PCM harness connector by-pass circuit, use a DVOM to check resistance between PCM harness connector IC circuit and reference low circuit. If resistance is greater than 6000 ohms, go to step 9). If resistance is not greater than 6000 ohms, go to next step.
  5. Turn ignition off. Disconnect ICM 14-pin connector. Check resistance between ICM 14-pin harness connector IC circuit and engine ground. If resistance is infinite, go to next step. If resistance is not infinite, go to step 10).
  6. Check by-pass circuit for open. If open is found, repair as necessary. After repairs, go to step 15). If open is not found, go to next step.
  7. Check by-pass circuit for faulty connection at ICM. If faulty connection is found, repair as necessary. After repairs, go to step 15). If connection is okay, go to step 14).
  8. Turn ignition off. Disconnect ICM 14-pin connector. Turn ignition on. If test light illuminates, go to step 11). If test light does not illuminate, go to step 14).
  9. Turn ignition off. Disconnect ICM connectors. Turn ignition on. Check IC circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 15). If no short to voltage is found, go to step 12).
  10. Locate and repair short to ground in IC circuit. After repairs, go to step 15).
  11. Locate and repair short to ground in by-pass circuit. After repairs, go to step 15).
  12. Check by-pass circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 15). If connection is okay, go to next step.
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 15).
  14. Replace ICM. After replacing module, go to next step.
  15. Read and record FAIL RECORDS data for DTC P1361. Clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1361 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1361 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect ICM. Connect a DVOM between ICM harness connector IC circuit and battery voltage. With ignition on, observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start and run, see ENGINE DOES NOT START in the «BASIC TESTING - 3.8L»(ref-20653) article.
  3. Using scan tool, read and record FAILS RECORD DATA. Operate vehicle within conditions noted in FAILED RECORDS DATA. Read SPECIFIC DTC. If scan tool displays DTC P1374 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1374 FAILED THIS IGN, see DIAGNOSTIC AIDS.
  4. Connect a test light to any injector harness connector. Turn ignition on. Connect repeatedly touch test light lead to 3X reference signal circuit while observing test light. If test light blinks, go to step 8). If test light does not flash, go to next step.
  5. Turn ignition off. Disconnect PCM. Check 3X reference signal circuit for open or short to ground. If a problem is found, go to step 11). If no problem is found, go to next step.
  6. Check for faulty 3X reference signal circuit connection at PCM. If connection is faulty, repair as necessary. After repairs, go to step 11). If connection is okay, go to next step.
  7. Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to step 10).
  8. Check for faulty connections at ICM. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connections are okay, go to next step.
  9. Replace ICM. After replacing module, go to step 11).
  10. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  11. Read and record FAIL RECORDS data for DTC P1374. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1374 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1374 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe a voltmeter connected to 3X reference circuit at PCM harness connector while moving all related harness and connectors. A change in voltage indicates fault location.

Check for incorrect harness routing near secondary ignition components, ignition coil arcing to wiring harness or ICM. Check ignition coils for cracks, carbon tracking or other signs of damage. Check for secondary ignition wire(s) arcing to wiring harness.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. After performing OBD system check, go to next step.
  2. Using scan tool, select DTC INFO and note if this DTC has failed this ignition cycle. If DTC failed, diagnose ABS system using the BRAKES SYSTEM - ANTI-LOCK article. If DTC did fail this ignition, go to next step.

If this DTC is set, it indicates that the ABS system has detected a malfunction which will not allow the EBCM to transmit correct rough road data to PCM.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to idle. Using scan tool, read EGR ACTUAL POS. If scan tool displays zero percent, go to next step. If scan tool does not display 0%, go to step 11).
  3. Turn ignition on. Select MISC TESTS on scan tool. Increment EGR valve from the 10 percent through the 100 percent positions while comparing the desired position with the actual position. If desired is close to actual, go to next step. If not, go to step 6).
  4. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using test light connected to ground, probe EGR ignition filter circuit at PCM connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 33)
  5. Turn ignition off. Reconnect PCM harness connector. Turn ignition on. Review and record FAIL RECORDS data. Operate vehicle within fail records conditions. Monitor SPECIFIC DTC for DTC P1406 until DTC test runs. If scan tool indicates this code failed this ignition, go to step 22). If not, see DIAGNOSTIC AIDS.
  6. Disconnect EGR valve harness connector. Connect a DVOM between EGR harness connector control and ignition feed circuits. Using scan tool, command EGR duty cycle to 100 percent position. If about battery voltage is present at 100 percent, go to step 17). If not, go to next step.
  7. Connect a test light between engine ground and EGR valve harness connector ignition feed circuit. If test light illuminates, go to step 9). If test light does not illuminate, go to next step.
  8. Check EGR valve ignition feed circuit fuse. If fuse is blown, locate and repair short to ground in ignition feed circuit. After repairs, go to step 34). If fuse is okay, go to step 24).
  9. Turn ignition off. Disconnect PCM connectors. Check EGR control circuit for open. If open is found, repair as necessary. After repairs, go to step 34). If no open is found, go to next step.
  10. Check for faulty EGR control circuit terminal connection at PCM. If connection is faulty, repair as necessary. After repairs, go to step 34). If connection is okay, go to step 32).
  11. Disconnect EGR valve harness connector. Using scan tool, read EGR ACTUAL POS. If scan tool displays zero percent, go to step 13). If scan tool does not display 0, go to next step.
  12. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Check voltage between engine grounds and EGR pintle position circuit. If voltage is about zero volts, go to step 31). If voltage is not as specified, go to step 26).
  13. Connect a test light between battery voltage and EGR harness connector sensor ground circuit. If test light illuminates, go to step 15). If test light does not illuminate, go to next step.
  14. Check sensor ground circuit for faulty connection at PCM or open between PCM and EGR valve. If a problem is found, repair as necessary. After repairs, go to step 34). If no problem is found, go to step 32).
  15. Connect a test light between battery voltage and EGR harness connector control circuit. If test light illuminates, go to step 16). If test light does not illuminate, go to step 22).
  16. Turn ignition off. Disconnect PCM. Turn ignition on. Connect test light between battery voltage and EGR control circuit. If test light illuminates, go to step 28). If test light does not illuminate, go to step 30).
  17. Check voltage between EGR valve harness connector sensor ground and 5-volt reference circuits. If voltage is 5 volts, go to next step. If voltage is not as specified, go to step 23).
  18. Connect test light between battery voltage and EGR valve harness connector pintle position circuit. If test light illuminates, go to step 21). If test light does not illuminate, go to next step.
  19. Connect a jumper wire between EGR valve connector 5-volt reference and pintle position circuits. Using scan tool, read EGR ACTUAL POS. If scan tool displays 100 percent, go to step 22). If scan tool does not display 100 percent, go to next step.
  20. Turn ignition off. Disconnect PCM connectors. Check pintle position circuit for open or faulty connection at PCM. If a problem is found, repair as necessary. After repairs, go to step 34). If no problem is found, go to step 32).
  21. Turn ignition off. Disconnect PCM connectors. Connect test light between battery voltage and pintle position circuit. If test light illuminates, go to step 29). If test light does not illuminate, go to step 30).
  22. Check for faulty connection at EGR valve. If faulty connection is found, repair as necessary. After repairs, go to step 33). If connection is okay, go to step 27).
  23. Check for open or short to ground in EGR 5-volt reference circuit. If a problem is found, go to step 34). If no problem is found, go to step 25).
  24. Locate and repair open ignition feed circuit. After repairs, go to step 34).
  25. Check EGR 5-volt reference circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 34). If connection is okay, go to step 32).
  26. Locate and repair short to voltage in pintle position circuit. After repairs, go to step 34).
  27. Replace EGR valve. After replacing EGR valve, go to step 34).
  28. Locate and repair short to ground in EGR control circuit. After repairs, go to step 34).
  29. Locate and repair short to ground in pintle position circuit. After repairs, go to step 34).
  30. Check pintle position circuit or EGR control circuit for short to sensor ground. Repair as necessary. After repairs, go to step 34). If circuits are okay, go to step 32).
  31. Check EGR pintle position circuit for short to 5-volt reference circuit. Repair as necessary. After repairs, go to step 34). If circuit is okay, go to next step.
  32. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  33. Locate and repair open in EGR ignition filter circuit. After repairs, go to next step.
  34. Read and record FAIL RECORDS data for DTC P1406. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1406 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1406 FAILED THIS IGN, repair is complete.

Check for excessive deposits on EGR valve pintle or seat. Check for faulty EGR valve. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool EGR ACTUAL POS display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If DTC P1655 is also set, diagnose DTC P1655 first. If DTC is not set, go to next step.
  3. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays zero in. H2O go to next step. If scan tool does not display zero in. H2O, repair faulty fuel tank pressure sensor circuit.
  4. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J-41413). Reinstall fuel cap. Read and record FAIL RECORDS data for DTC P1441. Clear DTCs. Connect EVAP pressure/purge cart to EVAP service port. Using scan tool, command EVAP vent solenoid ON (closed). Using EVAP pressure/purge cart, attempt to pressurize EVAP system to 5 in. H2O. If specified pressure is achieved, go to next step. If specified pressure is not achieved, to step 6).
  5. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays 5 in. H2O, go to next step. If scan tool does not display 5 in. H2O, repair faulty fuel tank pressure sensor circuit.
  6. Check EVAP purge vacuum and source line routing and connections at EVAP purge solenoid. If no problem is found, go to next step. If a problem is found, go to step 9).
  7. Disconnect engine vacuum source line from EVAP purge solenoid. Connect a hand vacuum pump to engine vacuum side of EVAP purge solenoid. Attempt to apply 15 in. Hg vacuum to EVAP canister. If vacuum is maintained as specified, see DIAGNOSTIC AIDS. If vacuum cannot be maintained as specified, go to next step.
  8. Replace EVAP purge solenoid. After replacing EVAP purge solenoid, go to step 10).
  9. Correct line routing and connections as necessary. After repairs, go to next step.
  10. Turn engine on. Remove fuel cap. Using scan tool OUTPUT TESTS function. Select and activate SEAL SYSTEM. Reinstall fuel cap. Run engine at 2500 RPM for 10 seconds while monitoring FUEL TANK PRESSURE on scan tool. If scan tool displays zero in. H2O, repair is complete. If scan tool does not display zero in. H2O, return to step 3).

Check for incorrect vacuum hose routing or damage. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool FUEL TANK PRESSURE display while moving all related harness and connectors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition on. Using scan tool, read CRUISE ENGAGED status. If scan tool displays YES, go to next step. If scan tool does not display YES, go to step 5).
  3. Turn ignition off. Disconnect PCM. Turn ignition on. Using a DVOM, check voltage between engine ground and cruise status circuit at PCM. If voltage reading is greater than 7 volts, go to next step. If voltage reading is not greater than 7 volts, go to step 9).
  4. Check for faulty cruise status circuit connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 14). If connection is okay, go to step 12).
  5. Turn ignition of. Disconnect Stepper Motor Cruise Control (SMCC) module connector. Turn ignition on. Connect a test light between engine ground and SMCC harness connector cruise inhibit circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  6. Turn ignition off. Disconnect PCM connectors. Connect test light between battery voltage and SMCC harness connector cruise inhibit circuit. If test light illuminates, go to step 13). If test light does not illuminate, go to step 12).
  7. Turn ignition off. Reconnect SMCC harness connector. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector cruise inhibit circuit. If DVOM voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 11).
  8. Clear DTCs. Start engine and read DTCs. If DTC P1554 resets, go to step 12). If DTC does not reset, see DIAGNOSTIC AIDS.
  9. Check cruise status circuit for open or short to ground. If a problem is found, repair as necessary and go to step 14). If no problem is found, go to next step.
  10. Check cruise status circuit for faulty connection at SMCC module. If faulty connection is found, repair as necessary. After repairs, go to step 14). If connection is okay, go to next step.
  11. Replace SMCC module. After replacing module, go to step 14).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 14).
  13. Locate and repair short to ground in cruise inhibit circuit. After repairs, go to next step.
  14. Clear DTCs. Start engine and read DTCs. If DTC P1554 resets, return to step 2). If DTC does not reset, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool CRUISE STATUS display while moving all related harness and connectors. A change in scan tool display indicates fault location.

Vehicle operation is disabled if incorrect key or starting procedure is used. Theft deterrent module enables crank circuit to starter and sends a signal to PCM if correct key is being used. If proper signal does not reach PCM fuel enable signal circuit, PCM will not pulse injectors on, disabling vehicle, even if crank circuit is by-passed. Signal should be 40-60 Hz and is measured using DVOM in Hertz scale.

Conditions required to set DTC are

  1. Engine running.
  2. PCM detects incorrect signal on Theft Deterrent System (TDS) fuel enable circuit.
  3. Listed conditions are present for more than 2 seconds.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Ensure battery is fully charged. Crank engine. If engine cranks, go to next step. If engine does not crank, diagnose and repair TDS.
  3. Turn ignition off. Disconnect TDS module connector. Turn ignition on. Using a DVOM, check voltage between TDS module harness connector ground and TDS fuel enable circuits. If voltage is about 5 volts, go to next step. If voltage is not as specified, go to step 6).
  4. Turn ignition off. Reconnect Body Control Module (BCM) connector. Turn ignition on. Using DVOM in Hertz (Hz) scale, check frequency between engine ground and TDS fuel enable circuit. If frequency is 40-60 Hz, go to next step. if frequency is not as specified, go to step 8).
  5. Turn ignition off. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, see DIAGNOSTIC AIDS. If engine does not start, go to step 7).
  6. Check TDS fuel enable circuit for open, short to ground or short to battery voltage. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to next step.
  7. Check TDS fuel enable circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to step 9).
  8. Check for faulty connection at TDS module. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to step 10).
  9. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 11).
  10. Replace BCM module. After replacing BCM, go to next step.
  11. Clear DTCs. Turn ignition on and observe VTD FUEL DISABLE scan tool display. If scan tool displays INACTIVE, repair is complete. If scan tool does not display INACTIVE, return to step 2)

Check for faulty connections or damaged harness. Disconnect TDS module connector. Turn ignition on. Connect a DVOM between engine ground and TDS module harness connector fuel enable circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Ensure battery is fully charged. Crank engine. If engine cranks, go to next step. If engine does not crank, diagnose and repair TDS.
  3. Turn ignition off. Disconnect TDS module connector. Turn ignition on. Using a DVOM, check voltage between TDS module harness connector ground and TDS fuel enable circuits. If voltage is about 5 volts, go to next step. If voltage is not as specified, go to step 6).
  4. Turn ignition off. Reconnect TDS module connector. Turn ignition on. Using DVOM in Hertz (Hz) scale, check frequency between engine ground and TDS fuel enable circuit. If frequency is 40-60 Hz, go to next step. if frequency is not as specified, go to step 8).
  5. Turn ignition off. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, see DIAGNOSTIC AIDS. If engine does not start, go to step 7).
  6. Check TDS fuel enable circuit for open, short to ground or short to battery voltage. If a problem is found, repair as necessary. After repairs, go to step 11). If no problem is found, go to next step.
  7. Check TDS fuel enable circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to step 9).
  8. Check for faulty connection at TDS module. If faulty connection is found, repair as necessary. After repairs, go to step 11). If connection is okay, go to step 10).
  9. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 11).
  10. Replace TDS module. After replacing module, go to next step.
  11. Clear DTCs. Turn ignition on and observe VTD FUEL DISABLE scan tool display. If scan tool displays INACTIVE, repair is complete. If scan tool does not display INACTIVE, return to step 2)

Check for faulty connections or damaged harness. Disconnect TDS module connector. Turn ignition on. Connect a DVOM between engine ground and TDS module harness connector fuel enable circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Ensure PCM and engine grounds are secure and clean. If a problem is found, go to step 14). If no problem is found, go to next step.
  3. Using scan tool, select DTC INFO, LAST TST FAIL. If DTC P0107, P0108, P0122, P0123, P1106, P1107, P1121, P1122 and/or P1406 also set, diagnose affected DTC before proceeding. If none of these DTCs are set, go to next step.
  4. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector ground and 5-volt reference "A" circuits. If voltage is greater than 5.5 volts, go to next step. If voltage is not greater than 5.5 volts, go to step 9).
  5. Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "A" circuits. Disconnect EGR valve. If voltage is greater than 5.5 volts, go to next step. If voltage is not greater than 5.5 volts, go to step 8).
  6. Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "A" circuits while sequentially disconnecting MAP and TP sensors. If voltage changes whenever any of these sensors is disconnected, locate and repair short to voltage in affected sensor signal circuit and go to step 14). If voltage does not change, go to next step.
  7. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "A" circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 14). If no short to voltage is found, go to step 13).
  8. Replace EGR valve. After replacing EGR valve, go to step 14).
  9. Turn ignition off. Reconnect PCM. Disconnect TP sensor, MAP sensor and EGR valve. Ignition on. Connect DVOM between TP sensor 5-volt reference circuit and TP sensor ground circuit. If voltage is less than 4.5 volts, go to step 12). If not, go to next step.
  10. With DVOM still connected to TP sensor 5-volt reference and ground circuits, reconnect (one at a time) MAP sensor and EGR valve. If voltage changes when one of the listed devices is reconnected, replace that component. After repairs, go to step 14). If voltage does not change, go to next step.
  11. Disconnect EGR valve. Connect DVOM between EGR connector 5-volt reference circuit and ground circuit. Reconnect TP sensor. If voltage measured on EGR connector changes, replace TP sensor. After replacing sensor, go to step 14). If not, go to step 13).
  12. Turn ignition off. Disconnect PCM connectors. Turn ignition on. check 5-volt reference "A" circuit for short to ground. If short to ground is found, repair as necessary. After repairs, go to step 14). If circuit is okay, go to next step.
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1635. If scan tool displays DTC P1635 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1635 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool MAP display while moving harness and connectors related to EGR valve, MAP and TP sensors. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Ensure PCM and engine grounds are secure and clean. If a problem is found, go to step 11). If no problem is found, go to next step.
  3. Ensure A/C is off. Observe A/C high side pressure on scan tool. If pressure displays a voltage of greater than 4.8 volts or less than 0.1 volt, go to «DTC P0530»(ref-20509-S04784708872001010200000) for diagnosis of pressure sensor circuit. If voltage displayed is not greater than 4.8 volts or less than 0.1 volt, go to next step.
  4. Unplug A/C pressure sensor connector. Using DVOM, check voltage between sensor ground circuit and sensor 5-volt reference circuit. If voltage is greater than 5.5 volts, go to next step. If not, go to step 7).
  5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. If voltage is greater than 5.5 volts, go to next step. If voltage is not greater than 5.5 volts, go to step 10).
  6. Locate and repair short to voltage in A/C refrigerant pressure sensor signal circuit. After repairs, go to step 11).
  7. If voltage is less than 4.5 volts, go to next step. If voltage is not less than 4.5 volts, go to step 9).
  8. Check for short to voltage in A/C pressure sensor signal circuit. Repair as necessary. After repairs, go to step 11). If no repairs are required, go to step 10).
  9. Ignition off. Disconnect PCM connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to ground. If short to ground is found, repair as necessary. After repairs, go to step 11). If no short to ground is found, go to next step.
  10. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  11. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1639. If scan tool displays DTC P1639 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1639 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool A/C PRESSURE display while moving harness and connectors related to A/C refrigerant pressure sensor. A change in scan tool display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector MIL driver circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 6).
  3. Using DVOM in 10-amp scale, check current between engine ground and MIL driver circuit for 2 minutes. If current remains at 0.05-0.50 amp, go to step 11). If current does not remain as specified, go to next step.
  4. Turn ignition off. With PCM connectors disconnected, disconnect I/P connectors. Turn ignition on. Using DVOM, check voltage between engine ground and MIL driver circuit. If voltage is zero volts, go to step 10). If voltage is greater than zero volts, go to next step.
  5. Locate and repair short to voltage in MIL driver circuit. After repairs, go to step 15).
  6. Check I/P indicators ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in I/P indicators ignition feed circuit. Replace fuse. After repairs, go to step 15).
  8. Disconnect I/P connectors. Turn ignition on. Check voltage between engine ground and I/P indicators ignition feed circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 13).
  9. Check MIL driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 15). If no problem is found, go to next step.
  10. Check MIL driver and I/P indicators ignition feed circuits for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 15). If connection is okay, diagnose and repair I/P assembly problem.
  11. Turn ignition off. Reconnect PCM connectors. Disconnect I/P connectors. Turn ignition on. Connect a test light between I/P harness connector MIL driver and ignition feed circuits. Using scan tool, cycle MIL on and off. If test light flashes on and off, see DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check MIL driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 15). If connection is okay, go to step 14).
  13. Locate and repair open I/P indicators ignition feed circuit. After repairs, go to step 15).
  14. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  15. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1641. If scan tool displays DTC P1641 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1641 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector MIL driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fan 1 relay driver circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 6).
  3. Using DVOM in 10-amp scale, check current between engine ground and fan 1 relay driver circuit for 2 minutes. If current remains .05-0.5 amp go to step 11). If current does not remain as specified, go to next step.
  4. Turn ignition off. Reconnect cooling fans. With PCM connectors still disconnected, disconnect fan 1 relay connector. Turn ignition on. Using DVOM, check voltage between engine ground and fan 1 relay driver circuit. If voltage is zero volts, go to step 10). If voltage is greater than zero volts, go to next step.
  5. Locate and repair short to voltage in fan 1 relay driver circuit. After repairs, go to step 16).
  6. Check fan 1 relay ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in fan 1 relay ignition feed circuit. Replace fuse. After repairs, go to step 16).
  8. Disconnect fan 1 relay connector. Turn ignition on. Check voltage between engine ground and fan 1 relay ignition feed circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 13).
  9. Check fan 1 relay driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 16). If no problem is found, go to next step.
  10. Check fan 1 relay driver and fan 1 relay ignition feed circuits for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 14).
  11. Turn ignition off. Reconnect PCM connectors. Disconnect fan 1 relay connector. Turn ignition on. Connect a test light between fan 1 relay harness connector fan 1 relay driver and ignition feed circuits. Using scan tool, cycle fan 1 relay on and off. If test light flashes on and off, go to DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check fan 1 relay driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 15).
  13. Locate and repair open fan 1 relay ignition feed circuit. After repairs, and go to step 16).
  14. Replace fan 1 relay. After replacing relay, go to step 16).
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  16. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1651. If scan tool displays DTC P1651 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1651 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector fan 1 relay driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fan 2 relay driver circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 6).
  3. Using DVOM in 10-amp scale, check current between engine ground and fan 2 relay driver circuit for 2 minutes. If current remains .05-0.5 amp go to step 11). If current does not remain as specified, go to next step.
  4. Ignition off. With PCM connectors still disconnected, disconnect series/parallel and high speed fan relays. Ignition on. Using DVOM, check voltage between engine ground and fan 2 relay driver circuit. If voltage is zero volts, go to step 10). If voltage is greater than zero volts, go to next step.
  5. Locate and repair short to voltage in fan 2 relay driver circuit. After repairs, go to step 18).
  6. Check fan 2 relay ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in fan 2 relay ignition feed circuit. Replace fuse. After repairs, go to step 18).
  8. Disconnect fan 2 relay connector. Turn ignition on. Check voltage between engine ground and fan 2 relay ignition feed circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 13).
  9. Check fan 2 relay driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 18). If no problem is found, go to next step.
  10. Check fan 2 relay driver and fan 2 relay ignition feed circuits for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 18). If connection is okay, go to DIAGNOSTIC AIDS.
  11. Turn ignition off. Reconnect PCM connectors. Disconnect high speed cooling fan relay connector. Turn ignition on. Connect a test light between fan 2 relay harness connector fan 2 relay driver and ignition feed circuits. Using scan tool, cycle fan 2 relay on and off. If test light flashes on and off, see DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check fan 2 relay driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 18). If connection is okay, go to step 15).
  13. Locate and repair open fan 2 relay ignition feed circuit. After repairs, go to step 18).
  14. Reconnect series/parallel cooling fan relay. Using DVOM tool on 10-amp scale, check current between engine ground and fan 2 relay driver circuit for 2 minutes. If current remains less than 0.75 amp but not zero, go to step 16). If current remains 0.75 amp or greater, go to step 17).
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 18).
  16. Replace high speed cooling fan relay. After replacing relay, go to step 18).
  17. Replace series/parallel cooling fan relay. After replacing relay, go to next step.
  18. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1652. If scan tool displays DTC P1652 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1652 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector fan 2 relay driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector A/C relay driver circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6).
  3. Disconnect A/C clutch connector. Using DVOM in 10 amp scale, check current between engine ground and A/C relay driver circuit for 2 minutes. If current remains .05-0.5 amp, go to step 11). If current does not remain .05-0.5 amp, go to next step.
  4. Ignition off. Reconnect A/C clutch connector. With PCM connectors still disconnected, disconnect A/C relay connector. Ignition on. Using DVOM, check voltage between engine ground and A/C relay driver circuit. If voltage reading is zero volts, go to step 10). If voltage reading is greater than zero volts, go to next step.
  5. Locate and repair short to voltage in A/C relay driver circuit. After repairs, go to step 16).
  6. Check A/C relay ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in A/C relay ignition feed circuit. Replace fuse. After repairs, go to step 16).
  8. Disconnect A/C relay connector. Turn ignition on. Check voltage between engine ground and A/C relay ignition feed circuit. If voltage reading is 9-16 volts, go to next step. If voltage reading is not 9-16 volts, go to step 13).
  9. Check A/C relay driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 16). If no problem is found, go to next step.
  10. Check A/C relay driver and ignition feed circuits for faulty connection at A/C relay and PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 14).
  11. Turn ignition off. Reconnect PCM connectors. Disconnect A/C relay connector. Turn ignition on. Connect a test light between A/C relay harness connector A/C relay driver and ignition feed circuits. Using scan tool, cycle A/C relay on and off. If test light flashes on and off, go to DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check A/C relay driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 15).
  13. Locate and repair open A/C relay ignition feed circuit. After repairs, go to step 16).
  14. Replace A/C relay. After replacing relay, go to step 16).
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  16. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1654. If scan tool displays DTC P1654 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1654 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector A/C relay driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing PBD system check, go to next step.
  2. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector EVAP purge solenoid driver circuit. If voltage is 9-16 volts, go to next step. If voltage is not 9-16 volts, go to step 6).
  3. Using DVOM in 10 amp scale, check current between engine ground and EVAP purge solenoid driver circuit for 2 minutes. If current remains .05-0.5 amp, go to step 11). If current does not remain .05-0.5 amp, go to next step.
  4. Turn ignition off. With PCM connectors still disconnected, disconnect EVAP purge solenoid connector. Turn ignition on. Using DVOM, check voltage between engine ground and EVAP purge solenoid driver circuit. If voltage reading is zero volts, go to step 10). If voltage reading is greater than zero volts, go to next step.
  5. Locate and repair short to voltage in EVAP purge solenoid driver circuit. After repairs, go to step 16).
  6. Check EVAP purge solenoid ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in EVAP purge solenoid ignition feed circuit. Replace fuse. After repairs, go to step 16).
  8. Disconnect EVAP purge solenoid connector. Turn ignition on. Check voltage between engine ground and EVAP purge solenoid ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13).
  9. Check EVAP purge solenoid driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 16). If no problem is found, go to next step.
  10. Check EVAP purge solenoid driver and ignition feed circuits for faulty connection at EVAP purge solenoid and PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 14).
  11. Turn ignition off. Reconnect PCM connectors. Disconnect EVAP purge solenoid connector. Turn ignition on. Connect a test light between EVAP purge solenoid harness connector EVAP purge solenoid driver and ignition feed circuits. Using scan tool, cycle EVAP purge solenoid on and off. If test light flashes on and off, see DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check EVAP purge solenoid driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 15).
  13. Locate and repair open EVAP purge solenoid ignition feed circuit. After repairs, go to step 16).
  14. Replace EVAP purge solenoid. After replacing EVAP purge solenoid, go to step 16).
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  16. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1655. If scan tool displays DTC P1655 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1655 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector EVAP purge solenoid driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector cruise inhibit driver circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6).
  3. Using DVOM in 10-amp scale, check current between engine ground and cruise inhibit driver circuit for 2 minutes. If current remains between .001 and 0.5 amp, go to step 11). If current does not remain as specified, go to next step.
  4. Turn ignition off. With PCM connectors disconnected, disconnect cruise inhibit connector. Turn ignition on. Using DVOM, check voltage between engine ground and Servo Motor Cruise Control (SMCC) module cruise inhibit driver circuit. If voltage reading is zero volts, go to step 10). If voltage reading is greater than zero volts, go to next step.
  5. Locate and repair short to voltage in cruise inhibit driver circuit. After repairs, go to step 16).
  6. Check SMCC module ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in SMCC module ignition feed circuit. Replace fuse. After repairs, go to step 16).
  8. Disconnect SMCC module connector. Turn ignition on. Check voltage between engine ground and SMCC module ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13).
  9. Check cruise inhibit driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 16). If no problem is found, go to next step.
  10. Check cruise inhibit driver and ignition feed circuits for faulty connection at SMCC module and PCM. If connection is faulty, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 14).
  11. Turn ignition off. Reconnect PCM connectors. Disconnect SMCC module connector. Turn ignition on. Connect a test light between SMCC module harness connector cruise inhibit driver and ignition feed circuits. Using scan tool, cycle cruise inhibit output on and off. If test light flashes on and off, see DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check cruise inhibit driver circuit for faulty connection at PCM. If connection is faulty, repair as necessary. After repairs, go to step 16). If connection is okay, go to step 15).
  13. Locate and repair open SMCC module ignition feed circuit. After repairs, go to step 16).
  14. Replace SMCC module. After replacing module, go to step 16).
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  16. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1662. If scan tool displays DTC P1662 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1662 FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector cruise inhibit driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 3.8L»(ref-20653) article. After performing OBD system check, go to next step.
  2. Turn ignition off. Disconnect PCM harness connector. Using DVOM, check voltage between affected PCM output circuit at PCM harness connector and ground. If voltage reading is near battery voltage, go to next step. If not, go to step 7).
  3. Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for at least 2 minutes. If current reads between 0.05-1.50 amps, go to step 11). If not, go to next step.
  4. Turn ignition off. Disconnect instrument panel cluster connector. Using DVOM, check voltage between affected PCM output circuit and ground. If voltage reading is zero volts, go to step 10). If voltage reading is not zero volts, go to next step.
  5. Locate and repair short to voltage in generator light control circuit. Repair as necessary. After repairs, go to step 15).
  6. Check ignition feed circuit for instrument cluster indicator lights. If fuse is open, replace fuse. After repairs, go to next step. If fuse is okay, go to step 8).
  7. Locate and repair short to ground in ignition feed circuit for instrument cluster indicators. Replace fuse. After repairs, go to step 15).
  8. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ground and ignition feed circuit terminal at instrument panel cluster connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13).
  9. Check for an open or short to ground in generator light control circuit. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to next step.
  10. Check generator light control circuit and ignition feed circuit for poor terminal connection at instrument panel cluster connector and at PCM connector. Repair as necessary. After repairs, go to step 15). If connections are okay, diagnose instrument panel assembly.
  11. Turn ignition off. Reconnect PCM connector. Disconnect instrument panel cluster connector. Turn ignition on. Connect a test light between generator light control circuit and ignition feed circuit terminals at instrument cluster connector. Using scan tool, select OUTPUTS TEST function and cycle generator light on and off. If test light flashes, see DIAGNOSTIC AIDS. If test light does not flash, go to next step.
  12. Check generator light control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 15). If connection is okay, go to step 14).
  13. Locate and repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 15).
  14. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  15. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P1655 until DTC P1655 test runs. If scan tool indicates FAILED THIS IGN, repeat step 2). If scan tool does not indicate FAILED THIS IGN, repair is complete.

Disconnect and inspect PCM harness connector. Inspect for damaged pins, corrosion and loose wires. An intermittent problem can be caused by a poor connection, rubbed-through wire insulation or broken wire inside insulation. Reviewing FAIL RECORDS vehicle mileage since diagnostic test last failed may help determine how often condition that caused DTC to set.

More articles — Engine Control System - Tests W/codes - 3.8L