Engine Controls Self-Diagnostics - 4.3l Chevrolet Blazer S15 рестайлинг

MODEL IDENTIFICATION

Vehicle model is identified by the fifth character of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

MODEL IDENTIFICATION

INTRODUCTION

To properly diagnose and repair this vehicle, follow DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no Diagnostic Trouble Codes (DTCs) are present and a no start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If no DTCs are present and a driveability condition exists, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

ON-BOARD DIAGNOSTICS

PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will store a Diagnostic Trouble Code (DTC) and, if code is emissions related, the Malfunction Indicator Light (MIL) located on instrument cluster will illuminate.

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

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

Code Types

There are 4 types of DTC categories

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

Freeze Frame/Failure Records

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

Typical data includes

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

Monitors

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

Intermittent Trouble Code Determination

Note. Intermittent is a DTC or symptom, with a condition that cannot be duplicated. Before attempting to diagnose an intermittent condition, ensure powertrain diagnostic system check has been performed. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK .

1. Duplicating Failure Conditions Freeze frame and failure records data contain the conditions present when DTC set. Review and record freeze frame and failure records data. Clear DTCs using scan tool. Turn ignition off and wait 15 seconds. Operate the vehicle under the same conditions noted in freeze frame and failure records data, as closely as possible. Vehicle must also be operating within conditions for running the DTC. See CODE ENABLE CRITERIA in appropriate DTC test. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed. An alternate method is to drive the vehicle with the DVOM connected to a suspected circuit. An abnormal reading on the DVOM when the problem occurs, may help you locate the problem.
2. Wiring Harness & Electrical Connectors Many intermittent open or shorted circuits come and go with harness or connector movement caused by vibration, engine torque, and bumps or rough pavement. Test for intermittents by moving related connectors and wiring while monitoring appropriate scan tool data. With engine running, move related connectors and wiring while monitoring engine operation. Verify if harness or connector movement affects scan tool data display, component or system operation, or engine operation. Repair condition as necessary. Intermittents caused by electrical connectors are usually caused by poor electrical connections, terminal tension and/or wiring problems. Check for poor mating of connector halves, terminals backed out or not fully seated in connector body, improperly formed or damaged terminals or poor terminal tension. Also check for poor terminal-to-wire connections including terminals crimped over insulation, swollen and stiff sections of wire in suspect circuits, wires that are broken inside the insulation, pinched, cut or rubbed-through wiring or wiring that is in contact with hot exhaust components. Repair condition as necessary.
3. Control Module & Component Power & Grounds Many vehicles have multiple circuits supplying power to control modules. Other components may have separate power circuits that may also need to be tested. Check connections at module or component connectors, fuses, and any intermediate connections between power source and the module or component. Ensure that the circuit can carry the current necessary to operate the component. Test all control module ground and system ground circuits. Control module may have multiple ground circuits. Other components may have separate grounds that may also need to be tested. Check grounds for clean and tight connections at the ground connection. Check the connections at the component and in splice packs, where applicable.
4. Temperature Sensitivity An intermittent condition may occur when a component or connection reaches normal operating temperature. Condition may occur only when component or connection is cold, or hot. Use freeze frame and failure records, scan tool snapshot or vehicle data recorder to help diagnose this type of intermittent. If intermittent is related to heat, check for high ambient temperatures, underhood or engine generated heat, circuit generated heat due to a poor connection, or high electrical load. If intermittent is related to cold, check for low ambient temperatures or water intrusion.
5. Electromagnetic Interference & Electrical Noise Some electrical components or circuits are sensitive to Electromagnetic Interference (EMI) or other types of electrical noise. Check for misrouted wiring that is too close to high voltage or high current devices. Check for wires that are too close to secondary ignition components, electrical motors or the generator. Check for non-factory or aftermarket add-on accessories such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, or cell phones. Test for open diode across AC compressor. Some relays may contain a clamping diode. Check that generator is operating properly.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in the 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. Diagnostic system check must be performed before using specific DTC testing procedure. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) .
2. If no DTCs are present and a driveability problem exists, refer to SYMPTOMS in appropriate TROUBLE SHOOTING - NO CODES article. Doing so will help identify proper system or component to check in appropriate SYSTEM & COMPONENT TESTING article.
3. After necessary repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation and ensure DTC does not reset.

RETRIEVING DIAGNOSTIC TROUBLE CODES

DTCs are retrieved using a Tech 2 scan tool, or other OBD-II compatible scan tool connected to OBD-II 16-pin Data Link Connector (DLC). See POWERTRAIN DIAGNOSTIC SYSTEM CHECK. (Scheme 1) DLC is located below left side of dash.

Scheme 1

POWERTRAIN DIAGNOSTIC SYSTEM CHECK

Note. Check for applicable Technical Service Bulletins (TSB) before proceeding. Perform the following procedure only if a driveability complaint exists, or if you were sent here from another procedure or article. DO NOT turn ignition off during the following procedure or clear DTCs unless instructed to do so.

1. Install scan tool. Turn ignition on, with engine off. Observe scan tool. If scan tool turns on, go to next step. If scan tool does not turn on, perform SCAN TOOL DOES NOT POWER UP under SYSTEM TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
2. Using scan tool, attempt to establish communication with Electronic Brake Control Module (EBCM), Instrument Panel Cluster (IPC), Heating, Ventilation and Air Conditioning (HVAC), Powertrain Control Module (PCM) and Vehicle Theft Deterrent Module (VTD). If scan tool communicates with all control modules, go to next step. If scan tool does not communicate with any of control module, perform SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
3. Attempt to start engine. If engine starts and idles, go to next step. If engine does not start, go to NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
4. Using scan tool, select DTC display function for EBCM, HVAC, IPC, PCM and VTD. If scan tool displays any DTCs, go to next step. If scan tool does not display any DTCs, go to step 9.
5. Using scan tool, select CAPTURED INFO in order to store PCM DTC information. After storing DTC information, go to next step.
6. If scan tool displays any "U" series DTCs, perform SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If scan tool does not display any "U" series DTCs, go to next step.
7. If DTC P0601, P0602, P0604 or P1683 is set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If DTC P0601, P0602, P0604 or P1683 is not set, go to next step.
8. If DTC P0562, P0563, P1637 or P1638 is set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If DTC P0562, P0563, P1637 or P1638 is not set, go to next step.
9. If problem is transmission related, diagnose transmission. See appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS in the appropriate TRANSMISSION SERVICE & REPAIR manual. If problem is not transmission related, go to next step.
10. If problem is I/M testing related, go to «INSPECTION/MAINTENANCE SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) under INSPECTION/MAINTENANCE PROCEDURES. If problem is not I/M testing related, go to next step.
11. Check for cause of hard start, surges/chuggles, lack of power, sluggishness, or sponginess. Check for cause of detonation/spark knock, hesitation, sag, stumble, cuts out, misses, poor fuel economy, rough/unstable, or incorrect idle and stalling. Check for cause of dieseling, run-on, backfire, MIL inoperative, or MIL always on. If problem is found, repair as necessary. See appropriate TROUBLESHOOTING - NO CODES article. If no problem is found, problem is intermittent.

CLEARING DIAGNOSTIC TROUBLE CODES

There are 3 methods to clear DTCs.

Scan Tool

Scan tool is preferable way to clear DTC information. Freeze frame and failure record data will also be cleared. PCM adaptive learning and system monitors will only be cleared for those system which had a stored DTC.

Disconnect Battery

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

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

Warm-up Cycles

If fault that caused DTC to set is repaired, PCM will begin to count warm-up cycles. After 40 consecutive warm-up cycles with no further faults, PCM will automatically clear DTC from memory.

SCAN TOOL USAGE

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

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

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

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

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

Scan Tool Display

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

The following are Tech 2 scan tool sub-menus in the DTC INFO and SPECIFIC DTC modes

1. DTC INFO MODE Used to search for specific type of stored DTC information. There are 7 choices in this mode. Technician may be instructed to test DTCs 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.
2. DTC STATUS This selection will display any DTCs 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. A DTC test that runs and passes will cause affected DTC to be removed from scan tool screen.
3. FAIL THIS IGN. This selection will display all DTCs that have failed during the present ignition cycle.
4. HISTORY This selection will display only DTCs that are stored in the control module's history memory. It will not display Type "D" DTCs. It will display all Type "A" and Type "B" DTCs that have the MIL illuminated and have failed within the last 40 warm-up cycles. It will also display Type "C" DTCs that have failed within the 40 warm-up cycles.
5. LAST TEST FAIL This selection will only display DTCs that have failed the last time the test ran. If Type "A" or "B" DTCs are displayed, the last test may have ran during the previous ignition cycle. For Type "C" DTCs, the last failure must have occurred during the current ignition cycle to be displayed as LAST TEST FAIL.
6. MIL REQUEST This selection will only display DTCs that are requesting MIL illumination. Type "C" DTCs cannot be displayed using this option. This selection will report Type "B" DTCs only after MIL illumination has been requested.
7. NOT RUN SCC Not Run Since Code Clear option will display up to 33 DTCs that have not run since DTCs were last cleared. Since any displayed DTCs have not run, their condition (passing or failing) is unknown.
8. 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 more than 40 warm-up cycles before this option is selected will not be displayed.
9. FAILED SINCE CLEAR This message indicates the DTC has failed at least once within the last 40 warm-up cycles since the last time DTCs were cleared.
10. NOT RUN SINCE CL. Not Run Since Cleared message indicates that the selected diagnostic test has not run since the last time DTCs were cleared. Therefore, the diagnostic test status (passed or failed) is unknown. After DTCs are cleared, this message will continue to be displayed until the diagnostic test runs.
11. NOT RUN THIS IGN. Not Run This Ignition message indicates the selected diagnostic test has not run this ignition cycle.
12. TEST RAN AND PASSED This message indicates the selected diagnostic test has: Passed the last test. Ran and passed during this ignition cycle. Ran and passed since DTCs were last cleared. Test has not failed since DTCs were last cleared. If this message is displayed, repair is complete. If FAILED THIS IGN. message is displayed, repair is incomplete and further diagnosis is required.

PCM LOCATION

On "L" and "M" Series, PCM is located on left side of engine compartment, near battery. On "S" and "T" Series, PCM is located on right side of engine compartment.

POWERTRAIN CONTROL MODULE

After replacing PCM or if program needs to be updated, refer to latest Techline® information on PCM reprogramming. After reprogramming, perform CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE .

CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE

Note. Battery must be fully charged and in good condition. Scan tool connection at DLC should be clean and tight before starting CKP system variation learn procedure.

1. Install scan tool to DLC.
2. Using scan tool, monitor PCM for DTCs. If other DTCs are set, except DTC P1336, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) .
3. Select CKP variation learn procedure on scan tool.
4. Observe fuel cut-off procedure.
5. Follow scan tool instructions when to block drive wheels, apply parking brake, cycle ignition from off to on, apply and hold brake pedal, start and idle engine, turn A/C off, place transmission in Park (A/T) or Neutral (M/T). Scan tool monitors certain component signals to determine if all conditions are met to continue with procedure. Scan tool only displays condition that inhibits the learn procedure and monitors CKP sensors activity. If there is a CKP or CMP sensor condition, refer to applicable DTC displayed. If ECT is not warm enough, operate engine at idle until ECT reaches specified temperature.
6. Using scan tool, enable CKP system variation learn procedure.
7. Slowly increase engine speed to observed RPM.
8. Immediately release throttle when fuel cut-off is reached.
9. If scan tool displays LEARNED THIS IGNITION, go to next step. If scan tool does not display LEARNED THIS IGNITION and no additional DTCs are set, perform «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . If a DTC is set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) .
10. Turn ignition off for 30 seconds after learn procedure is completed successfully.

DRIVE CYCLES

For drive cycle procedure, see INSPECTION/MAINTENANCE SYSTEM CHECK.

Description

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

Diagnostic Procedures

1. Perform «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under POWERTRAIN DIAGNOSTIC SYSTEM CHECKS. If DTC or driveability concern was repaired using powertrain diagnostic system check, go to step 3 . If no DTC or driveability concern was repaired using powertrain diagnostic system check, go to next step.
2. Review any service bulletins for software updates that may prevent I/M readiness. Perform any reprogramming or repairs indicated by the service bulletins. If reprogramming or repair service was required, go to «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If reprogramming or repair service was not required, go next step.
3. Using scan tool, observe the I/M System Status display. If more than one test is indicating a NO status, go to «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If a YES status is indicated, go to «INSPECTION/MAINTENANCE SYSTEM DTC TABLE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .

This procedure satisfies enable criteria necessary to execute all monitor diagnostics, and complete trips for those particular diagnostics. When all diagnostic tests have been completed, I/M System Status indicators are set to YES. Perform this test when more than one or all I/M System Status indicators are set to NO.

Ensure vehicle meets the following conditions before performing procedure

Enable Criteria

1. BARO pressure is greater than 74 kPa.
2. Engine coolant temperature and intake air temperature are less than 86°F (30°C).
3. Difference between intake air temperature and engine coolant temperature is 14°F (8°C) or less.
4. Battery voltage is 9-18 volts and fuel level is 1/4-3/4 tank.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Preprogram scan tool with vehicle information before ignition is turned on. Ensure vehicle meets conditions under conditions for running the DTC. See «ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__enable-criteria) . Turn off all accessories, such as A/C, blower fan, etc. Set vehicle parking brake. Ensure transmission is in Park (A/T) or Neutral (M/T). Start engine and allow to idle for 2 minutes, then go to next step.
3. Accelerate vehicle at part throttle to 55 MPH and maintain with this speed until engine reaches operating temperature. This may be up to 8-10 minutes depending on start-up coolant temperature. Continue operation under these conditions for an additional 6 minutes, then go to next step.
4. Reduce vehicle speed to 45 MPH, maintain this speed for one additional minute. Perform 4 decelerations of 25 seconds each from 45 MPH while maintaining the following criteria: Throttle closed. No brake application. No clutch actuation on M/T. No manual downshift Vehicle speed remains greater than 25 MPH. After each deceleration period, vehicle is returned to 45 MPH under part throttle acceleration and speed is maintained for 15 seconds, then go to next step.
5. Accelerate vehicle at part throttle to 45-55 MPH and maintain speed for 2 minutes. Decelerate to zero MPH. Operate engine at idle for 2 minutes while service brake is depressed, A/T in Drive or M/T in Neutral with clutch pedal depressed, then go to next step.
6. Using scan tool, observe I/M System Status display. If all I/M System Status indicators update to YES, go to next step. If not all I/M System Status indicators update to YES, repeat procedure.
7. Using scan tool, observe emission related DTC portion of I/M System Status display. If scan tool indicates any emission related DTCs, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If scan tool does not indicate emission related DTCs, system is okay.

Diagnostic Aids

Rough road conditions may prevent some tests from running. Extreme high or low ambient temperatures may prevent tests such as HO2S heater and evaporative emission system from initiating. If step is interrupted before completion, perform remaining portion of test procedures. Any portion of test procedure that requires the engine at operating temperature may be repeated. This allows most diagnostics to run and the remaining tests can be performed using individual system set procedures.

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

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

The following DTCs are required to set system status to YES

1. P0133/P0153, P0140, P1133/P1153 and P1134/P1154 - Oxygen Sensor
2. P0135, P0141 and P0155 - Oxygen Sensor Heater
3. P0401, P0404, P0405 and P1404 - EGR
4. P0420 or P0430 - Catalyst System
5. P0440, P0442, P0446 and P1441 - EVAP System

Diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .

The following DTCs are required to set system status to YES

1. P0133/P0153, P0140, P1133/P1153 and P1134/P1154 - Oxygen Sensor
2. P0135 - Oxygen Sensor Heater
3. P0401, P0404, P0405 or P1404 - EGR
4. P0410 and P1415/P1416 - Secondary AIR System
5. P0420 or P0430 - Catalyst System
6. P0440, P0442, P0446 and P1441 - EVAP System

Diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Secondary Air Injection (AIR) system. The test may be used to set the I/M System Status to YES.

Passive Test

1. Engine coolant temperature is 158-230°F (70-110°C).
2. Intake air temperature is 36-212°F (2-100°C).
3. Battery voltage greater than 11.7 volts.
4. Active test, if required, begins after engine goes into closed-loop.

Active Test

1. Engine coolant temperature is 158-230°F (70-110°C).
2. Intake air temperature is 36°F (2°C).
3. Battery voltage greater than 11.7 volts.
4. System operating in closed-loop.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . After performing I/M system check, go to next step.
2. Turn off all accessories (e.g., A/C, blower fan, etc.). Start engine and allow to idle for 2 minutes. Accelerate vehicle at part throttle to 45 MPH and maintain this speed for 3 minutes or until I/M System Status indicator updates to YES. Using scan tool, review I/M System Status display. If status updates to YES, go to step 5 . If status does not update to YES, go to next step.
3. Using scan tool, observe DTC Information. If DTCs are set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are set, go to next step.
4. Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter DTC in Specific DTC menu on scan tool. Operate vehicle within the «ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . Repeat procedure until scan tool indicates that diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Using scan tool, observe I/M System Status display. If status updates to YES, go next step. If status does not update to YES, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Using scan tool, observe emission related DTC portion of I/M System Status display. If scan tool indicates any emission related DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

The AIR pump generally operates once per ignition cycle, usually upon initial start up before engine goes into closed-loop fuel control.

If diagnostic test does not run, observe fuel trim correction. If fuel trim correction is more than plus or minus 4 percent, the AIR system test may not run. If status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

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

The first failure of a Type "B" DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. These conditions may include a partial to complete engine cool down. The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass. If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning ON, may cause the test to abort. If a diagnostic test is difficult to run, observe the I/M System Status display while maintaining the necessary enable conditions until the system status updates to YES.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the catalyst system. Test may be used to set the I/M System Status indicators to YES.

1. Barometric pressure is greater than 74 kPa.
2. Engine coolant temperature is 160-248°F (71-120°C).
3. Intake air temperature is 5-167°F (-15 to 75°C).
4. Engine operating in closed-loop.
5. Engine has run for 6-8 minutes off idle in order to initiate test.
6. Battery voltage is 11-18 volts.

Failure to meet the necessary requirements may produce inaccurate test results.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . After performing I/M system check, go to next step.
2. Accelerate vehicle at part throttle to 55 MPH and maintain speed for 5 minutes. Stop vehicle (zero MPH). Operate engine at idle for 2 minutes with service brake depressed, transmission in Drive (A/T) or in Neutral with clutch pedal depressed (M/T). Using scan tool, observe I/M System Status display. If catalyst system status updates to YES, go to step 5 . If catalyst system status does not update to YES, go to next step.
3. Using scan tool, observe DTC Information. If DTCs are set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are set, go to next step.
4. Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter DTC in Specific DTC menu on scan tool. Operate vehicle within the «ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . Repeat procedure until scan tool indicates the diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Using scan tool, observe I/M System Status display. If status updates to YES, go next step. If status does not update to YES, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Using scan tool, observe emission related DTC portion of I/M System Status display. If scan tool indicates any emission related DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

The control module runs a maximum of 6 tests per trip until the catalyst system status updates to YES. If status does not update, the test outlined in this test can be repeated until the I/M System Status updates to YES.

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

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

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

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Exhaust Gas Recirculation (EGR) system. The test may be used to set the I/M System Status indicators to YES.

1. BARO pressure is greater than 70 kPa.
2. Engine coolant temperature is 140-244°F (60-118°C).
3. Intake air temperature is less than 167°F (75°C).

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . After performing I/M system check, go to next step.
2. Accelerate vehicle at part throttle to 45 MPH and maintain speed for one minute. Decelerate 4 times for 25 seconds after accelerating from 45 MPH. Ensure throttle is closed, brakes are not applied, no clutch actuation on M/T and no manual downshift. When decelerating, ensure speed does not drop to less than 25 MPH and returned to 45 MPH under part throttle acceleration and speed is maintained for 15 seconds. Using scan tool, observe I/M System Status display. If catalyst system status updates to YES, go to step 5 . If catalyst system status does not update to YES, go to next step.
3. Using scan tool, observe DTC Information. If DTCs are set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are set, go to next step.
4. Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter DTC in Specific DTC menu on scan tool. Operate vehicle within the «ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . Repeat procedure until scan tool indicates the diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Using scan tool, observe I/M System Status display. If status updates to YES, go next step. If status does not update to YES, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Using scan tool, observe emission related DTC portion of I/M System Status display. If scan tool indicates any emission related DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

The control module only runs the EGR Active Tests during a gradual deceleration with a closed throttle and vehicle speed greater than 25 MPH. Several deceleration cycles may be necessary in order to accumulate a sufficient number of EGR flow samples. The procedure is for a clear, flat road. If procedure is performed on a road with a slight down hill grade, the test may acquire the necessary sample counters in one or 2 decel trips. If test is interrupted during the test, the test may take more than 3 deceleration cycles in order to complete. If status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

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

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

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

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Evaporative Emission (EVAP) system. The test may be used to set the I/M System Status indicators to YES.

1. BARO pressure is greater than 75 kPa.
2. Fuel level is 1/4-3/4.
3. Battery voltage is 10-18 volts.
4. Difference between engine coolant temperature and intake air temperature is less than 14°F (8°C).
5. Engine coolant temperature and intake air temperature are 39-86°F (4-30°C).

Test will initiate only after a cold start. Failure to meet the necessary requirements may produce inaccurate test results.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . After performing I/M system check, go to next step.
2. Using a scan tool, select Special Functions. Determine if vehicle is equipped with a service bay test for EVAP system. If vehicle is equipped with EVAP service bay test, go to next step. If vehicle is not equipped with EVAP service bay test, go to step 5 .
3. Turn off all accessories (e.g., A/C, blower fan, etc.). Using scan tool, perform EVAP Service Bay Test. If EVAP system passes test, go to step 8 . If EVAP system does not pass the test, go to next step.
4. Observe scan tool service bay test for indication of why the test did not pass (e.g., failed DTC, test aborted, etc.). Repair as necessary. After repairs, go to «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Turn off all accessories (e.g., A/C, blower fan, etc.). Once engine is started, DO NOT turn engine off for the remainder of the procedure or until test is complete. Start and operate engine at idle. Accelerate vehicle at part throttle to 45 MPH and maintain speed until engine reaches normal operating temperature. Continue for an additional 3 minutes after engine reaches normal operating temperature, or until I/M System Status indicator updates to YES. If EVAP system status updates to YES, go to step 8 . If EVAP system status does not update to YES, go to next step.
6. Using scan tool, observe DTC Information. If scan tool indicates any failed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, go to next step.
7. Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter DTC number in the Specific DTC menu of scan tool. Operate vehicle within the «ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . Repeat procedure until scan tool indicates the diagnostic test has run. Repeat step 4 for any additional required DTCs that have not run. Using scan tool, observe I/M System Status display. If EVAP system status updates to YES, go to next step. If EVAP system status does not update to YES, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
8. Using scan tool, observe the emission related DTC portion of I/M System Status display. If scan tool indicates any emission related DTCs set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

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

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

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the HO2S/O2S system. Test may be used to set the I/M System Status to YES. Ensure vehicle meets the requirements listed in conditions for running before performing this test.

1. Engine coolant temperature is greater than 135°F (57°C).
2. Engine operating in closed-loop.
3. Engine has been running for more than 160 seconds.
4. Battery voltage is 9-18 volts.

Failure to meet the necessary requirements may produce inaccurate test results.

1. Perform I/M system check. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . After performing I/M system check, go to next step.
2. Ensure vehicle is within the conditions for running this procedure. See «ENABLING CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . Turn all accessories off (e.g., A/C, blower fan, etc.). Start and operate engine at idle. Accelerate vehicle at part throttle to 45-55 MPH and maintain speed for 6 minutes or until the I/M System Status updates to YES. On vehicles with a either a 5-speed or 6-speed M/T may require operation in 4th or 5th gear respectively, in order for this test to run. Using scan tool, review I/M System Status display. If HO2S/O2S system status updates to YES, go to step 5 . If HO2S/O2S system does not update to YES, go to next step.
3. Using a scan tool, observe the DTC Information. If scan tool indicates any failed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If scan tool does not indicate any failed DTCs, go to next step.
4. Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter DTC number in the Specific DTC menu of scan tool. Operate vehicle within the conditions for running this procedure. See «ENABLING CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Using scan tool, observe the I/M System Status display. If HO2S/O2S system status updates to YES, go to next step. If HO2S/O2S system status does not update to YES, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Using scan tool, observe the emission related DTC portion of the I/M System Status display. If scan tool indicates any emission related DTCs set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If scan tool does not indicate any emission related DTCs set, system is okay.

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

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

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for Heated Oxygen Sensor (HO2S) system. The test may be used to set the I/M System Status to YES. Ensure vehicle meets the requirements listed in conditions for running DTC before performing this test.

Enabling Criteria

1. Engine coolant temperature and intake air temperature are less than 122°F (50°C).
2. Difference between intake air temperature and engine coolant temperature is less than 14°F (8°C).
3. Battery voltage is 11-18 volts.

Failure to meet the necessary requirements may produce inaccurate test results.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Preprogram scan tool with vehicle information before turning ignition on. Ensure vehicle is within the conditions for running DTC. Set parking brake. Verify transmission is in Park (A/T) or Neutral (M/T). Turn off all of accessories (e.g., A/C, blower fan, etc.). Start and allow engine to idle. Operate engine at idle until I/M System Status indicator updates to YES. If HO2S heater system status updates to YES within 2 minutes, go to step 5 . If HO2S heater system status does not update to YES within 2 minutes, go to next step.
3. Using scan tool, observe DTC information. If scan tool indicates any failed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If scan tool does not display any DTCs, go to next step.
4. Using scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the Specific DTC menu of scan tool. Operate vehicle within the conditions for running this procedure. See «ENABLING CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__enabling-criteria) . Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this step for any additional required DTCs that have not run. Using scan tool, observe I/M System Status display. If HO2S Heater System Status updates to YES, go to next step. If HO2S Heater System Status does not update to YES, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Using scan tool, observe emission related DTC portion of I/M System Status display. If scan tool indicates any emission related DTCs set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

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

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

SUMMARY

If no Diagnostic Trouble Codes (DTCs) are present and a no start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If no DTCs are present and a driveability condition exists, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

DIAGNOSTIC TROUBLE CODE DEFINITIONS

Note. DTCs are retrieved using a Tech 2 scan tool, or other OBD-II compatible scan tool connected to OBD-II 16-pin Data Link Connector (DLC).

DIAGNOSTIC TROUBLE CODE DEFINITIONS

MIL INOPERATIVE

Note. For circuit reference, see appropriate WIRING DIAGRAM article.

Scheme 2

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. On "L" and "M" Series, check RADIO BATT fuse. On "S" and "T" Series, check GAUGES fuse. Fuse on both models is located in passenger compartment fuse/relay block. If fuse is open, go to step 10. If fuse is okay, go to next step.
3. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Connect fused jumper wire (3-amp) between ground and PCM harness connector C2 terminal No. 46 (Brown/White wire). (Scheme 2) Observe MIL. If MIL illuminates, go to step 9. If MIL does not illuminate, go to next step.
4. Turn ignition off. Check fuse in jumper wire. If fuse is open, go to step 11. If fuse is okay, go to next step.
5. Remove Instrument Panel Cluster (IPC) harness connector. Check for open in Brown/White wire between IPC harness connector terminal A1 ("L" and "M" Series) or A11 ("S" and "T" Series) and PCM harness connector C2 terminal No. 46. Repair as necessary. After repairs, go to step 14. If circuit is okay, go to next step.
6. Turn ignition on, with engine off. Using test light connected to ground, probe IPC harness connector terminal B9 (Orange wire) on "L" and "M" Series or terminal A7 (Pink wire) on "S" and "T" Series. If test light illuminates, go to step 8. If test light does not illuminate, go to next step.
7. Turn ignition off. Repair open Orange or Pink wire between IPC and fuse block. After repairs, go to step 14.
8. Turn ignition off. Check IPC harness connector for poor connections. Repair as necessary. After repairs, go to step 14. If connections are okay, go to step 12.
9. Turn ignition off. Check PCM harness connector for poor connections. Repair as necessary. After repairs, go to step 14. If connections are okay, go to step 13.
10. Repair short to ground in Orange or Pink wire between fuse block and IPC harness connector terminal. See WIRING DIAGRAMS article. After repairs, go to step 14.
11. Repair short to voltage in Brown/White wire between IPC and PCM. After repairs, go to step 14.
12. Replace IPC assembly. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step 14.
13. Replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After repairs, go to next step.
14. Operate system to verify repair.

MIL ON STEADY

Note. For circuit reference, see appropriate WIRING DIAGRAM article.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Observe MIL. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 5.
3. Turn ignition off. Remove Instrument Panel Cluster (IPC). Check for short to ground in Brown/White wire between PCM harness connector C2 terminal No. 46 and IPC harness connector terminal A11. (Scheme 2) Repair as necessary. After repairs, go to step 6. If circuit is okay, go to next step.
4. Replace IPC assembly. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step 6.
5. Turn ignition off. Replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After repairs, go to next step.
6. Operate system to verify repair.

DIAGNOSTIC TESTS

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

Note. If PCM is replaced, NEW PCM must be programmed using special or required manufacturer's equipment. See POWERTRAIN CONTROL MODULE under PROGRAMMING.

DTC P0101: MASS AIRFLOW SYSTEM PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS article.

Circuit Description

Mass Airflow (MAF) sensor is an airflow meter that measures amount of air entering engine. PCM uses MAF sensor signal in order to provide correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering engine indicates a deceleration or idle. A large quantity of air entering engine indicates an acceleration or high load condition.

PCM applies voltage to sensor on signal circuit. Sensor uses the voltage in order to produce a frequency based on inlet airflow through the sensor bore. The frequency varies within a range of around 2000 Hertz at idle to about 10,000 Hertz at maximum engine load. PCM uses inputs from the MAP, IAT and engine speed in order to calculate a predicted MAF value.

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

Code Enable Criteria

Conditions for running DTC

1. DTCs P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0121, P0122, P0123, P0335, P0336, P0401, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1111, P1112, P1121, P1122 and P1441 is not set
2. Engine is running.
3. Ignition 1 signal is 11-18 volts.
4. TP sensor angle is less than 5 or 100 percent.
5. MAP sensor is less than 80 kPa.
6. Change in MAP sensor is less than 3 kPa.
7. Conditions are met for 2 seconds.

Conditions for setting DTC

1. PCM detects that actual MAF sensor frequency signal is not within a predetermined range of calculated MAF value for more than 4 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, monitor DTC information. If scan tool displays any other DTCs set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If scan tool does not display any other DTCs, go to next step.
3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__code-enable-criteria) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Allow engine to reach operating temperature. Observe MAP sensor voltage on scan tool. If MAP sensor voltage is 0.8-4.0 volts, go to next step. If MAP sensor voltage is not 0.8-4.0 volts, go to «DTC P0106»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0106-manifold-absolute-pressure-system) .
5. Operate engine at idle. Observe MAP sensor kPa reading on scan tool. Increase engine speed slowly to 3000 RPM and then back to idle. If MAP sensor reading changes smoothly and gradually through the test range, go to next step. If MAP sensor reading does not change smoothly and gradually through the test range, go to «DTC P0106»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0106-manifold-absolute-pressure-system) .
6. Turn ignition on, with engine off. Observe TP sensor angle from closed throttle to WOT (zero to 100 percent). Depress accelerator pedal completely and then release accelerator pedal. If scan tool indicates that TP sensor angle changed smoothly and completely through the test range, go to next step. If scan tool does not indicate that TP sensor angle does not change smoothly and completely through the test range, go to «DTC P0121»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0121-throttle-position-sensor-performance) .
7. Turn ignition off. Check for restricted air intake duct, collapsed air intake duct, misaligned air intake duct, dirty air filter element, deteriorating air filter element, objects blocking the air inlet screen of MAF sensor, debris on the sensing elements of MAF sensor, vacuum leak downstream of MAF sensor, poor vacuum connection at MAP sensor, or restricted exhaust system. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to next step.
8. Check for intermittent and for poor connection at MAF sensor. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to next step.
9. Replace MAF sensor. After replacing sensor, go to next step.
10. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__code-enable-criteria) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If scan tool does not display any DTCs, system is okay.

Ensure MAF sensor harness is not routed too close to secondary ignition wires or coils, solenoids, relays, or motors. Check throttle plate for sticking, or deposits on throttle plate or throttle bore. A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Check for any vacuum leaks downstream of MAF sensor. A Wide Open Throttle (WOT) acceleration from a stop should cause MAF sensor grams/second display on scan tool to increase rapidly. This increase should be from 6-12 grams/second at idle to 130 grams/second or more at time of the 1-2 shift. If increase is not observed, check for a restriction in the induction system or exhaust system.

The Barometric Pressure (BARO) sensor is used in order to calculate the predicted MAF value is initially based on MAP sensor at key on. When engine is running, MAP sensor value is continually updated near WOT. A skewed MAP sensor will cause the calculated mass airflow value to be inaccurate. The value shown for MAP sensor display varies with altitude. With ignition on, and engine off, 103 kPa is the approximate value near sea level. This value will decrease by about 3 kPa for every 1000 feet of altitude. A high resistance on the ground circuit of MAP sensor may cause this DTC to set. Any loss of vacuum to MAP sensor may cause this DTC to set. A high resistance in ignition voltage circuit of MAF sensor may cause this DTC to set.

DTC P0102: MASS AIRFLOW SENSOR CIRCUIT - LOW FREQUENCY

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 3

Mass Airflow (MAF) sensor is an airflow meter that measures amount of air entering engine. PCM uses MAF sensor signal in order to provide correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering engine indicates a deceleration or idle. A large quantity of air entering engine indicates an acceleration or high load condition.

PCM applies voltage to sensor on signal circuit. Sensor uses the voltage in order to produce a frequency based on inlet airflow through the sensor bore. The frequency varies within a range of around 2000 Hertz at idle to about 10,000 Hertz at maximum engine load. PCM uses inputs from the MAP, IAT and engine speed in order to calculate a predicted MAF value.

Conditions for running DTC

1. The engine is running for more than 2 seconds.
2. Engine speed is greater than 400 RPM.
3. Ignition 1 signal is greater than 8 volts.
4. MAF sensor frequency is stable for more than one second.

Conditions for setting DTC

1. PCM detects that MAF sensor frequency signal is less than 1300 Hz.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, observe MAF sensor frequency. If MAF sensor frequency is less than 1300 Hz, go to step 4. If MAF sensor frequency is not less than 1300 Hz, go to next step.
3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Observe MAF sensor frequency on scan tool. Move MAF sensor harness and connector. If movement of harness or connector affects MAF sensor frequency, go to step 25. If movement of harness or connector does not affect MAF frequency, go to next step.
5. Turn ignition off. Check for restricted air intake duct, collapsed air intake duct, misaligned air intake duct, dirty air filter element, deteriorating air filter element, any objects blocking air inlet screen of MAF sensor, debris on sensing elements of MAF sensor, vacuum leak downstream of MAF sensor, MAF sensor installed backwards, or restricted exhaust system. Repair as necessary. After repairs, go to step 30. If no problem is found, go to next step.
6. Check ENG 1 fuse in the ignition 1 voltage circuit of MAF sensor. Fuse is located in underhood fuse block. If fuse is open, go to step 12. If fuse is okay, go to next step.
7. Disconnect MAF sensor harness connector. MAF sensor is located in air intake. Turn ignition on, with engine off. Connect a test light between a good ground and MAF sensor harness connector terminal "C" (Pink wire). (Scheme 3) Does the test light illuminates, go to next step. If test light does not illuminate, go to step 17.
8. Connect test light between MAF sensor harness connector terminals "B" (Black wire on "L" and"M" Series or Black/White wire on "S" and "T" Series). If test light illuminates, go to next step. If test light does not illuminate, go to step 18.
9. Check voltage between a known-good ground and MAF sensor harness connector terminal "A" (Yellow wire). If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 11.
10. Connect a fused jumper wire between a known-good ground and MAF sensor harness connector terminal "A" (Yellow wire). Start engine. Using scan tool, check if any additional DTCs are set. If additional DTCs are set, go to step 23. If no additional DTCs are set, go to step 26.
11. If voltage is less than 4.5 volts, go to step 13. If voltage is not less than 4.5 volts, go to step 15.
12. Using a DVOM, check for continuity of Pink wire between MAF sensor and ground. If continuity exists, go to step 16. If continuity does not exist, go to step 26.
13. Turn ignition off. Disconnect PCM harness connector C2. Check for high resistance or open in Yellow wire between MAF sensor harness connector terminal "A" and PCM harness connector C2, terminal No. 31. (Scheme 2)and (Scheme 3). If continuity exists, go to next step. If continuity does not exist, go to step 19.
14. Check Yellow wire for continuity to ground. If continuity exists, go to step 21. If continuity does not exist, go to step 16.
15. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Check voltage between a known-good ground and MAF sensor harness connector terminal "A" (Yellow wire). If voltage reading is about zero volts, go to next step. If voltage reading is not about zero volts, go to step 22.
16. Check for continuity between PCM harness connector C2 terminal No. 31 and MAF sensor harness connector terminal "A" (Yellow wire). If continuity exists, go to step 24. If continuity does not exist, go to 27.
17. Turn ignition off. Repair short to ground in Pink wire. Replace fuse as necessary. After repairs, go to step 30.
18. Turn ignition off. Repair open in Pink wire. After repairs, go to step 30.
19. Repair high resistance or open in Black wire ("L" and "M" Series) or Black/White wire ("S" and "T" Series). After repairs, go to step 30.
20. Repair high resistance or open in Yellow wire. After repairs, go to step 30.
21. Repair short to ground in Yellow wire. After repairs, go to step 30.
22. Replace MAF sensor. After replacing sensor, go to step 30.
23. Turn ignition off. Repair short to voltage in Yellow wire. After repairs, go to step 30.
24. Repair circuits that are shorted together. After repairs, go to step 30.
25. Turn ignition off. Repair harness or connections as needed. After repairs, go to step 30.
26. Check for intermittent and poor connection at MAF sensor. Repair as necessary. After repairs, go to step 30. If no problem is found, go to step 28.
27. Check for intermittent and poor connection at PCM. Repair as necessary. After repairs, go to step 30. If no problem is found, go to step 29.
28. Replace MAF sensor. After replacing sensor, go to step 30.
29. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
30. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
31. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check PCM connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection. Check MAF sensor harness routing to ensure it is not too close to high-voltage wires such as spark plug leads. Check wiring harness for damage. Check for low minimum air rate through the sensor bore. Check for any vacuum leaks downstream of MAF sensor.

Perform a wide open throttle acceleration from a stop. It should cause MAF sensor grams/second display on scan tool to increase rapidly. This increase should be from 6-12 grams/second at idle to 130 grams/second or more at the time of the 1-2 shift. If increase is not observed, check for a restriction in the induction system or exhaust system. A resistance of 20 ohms or greater on MAF sensor ground circuit can cause this DTC to set.

DTC P0103: MASS AIRFLOW SENSOR CIRCUIT - HIGH FREQUENCY

Note. For circuit reference, see WIRING DIAGRAMS article.

Mass Airflow (MAF) sensor is an airflow meter that measures amount of air entering engine. The PCM uses MAF sensor frequency signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering engine indicates a deceleration or idle. A large quantity of air entering engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, ground circuit and a signal circuit.

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

Conditions for running DTC

1. Engine is running for more than 2 seconds.
2. Engine speed is greater than 400 RPM.
3. Ignition 1 signal is greater than 8 volts.
4. MAF sensor frequency is stable for more than one second.

Conditions for setting DTC

1. PCM detects that MAF sensor frequency signal is greater than 12,000 Hz.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
3. Turn ignition off. Disconnect MAF sensor harness connector. Start and operate engine at idle. Using scan tool, monitor MAF display. If scan tool display is zero Hz, go to next step. If scan tool display is not zero Hz, go to step 5 .
4. Turn ignition off. Check MAF sensor harness for incorrect routing. Ensure it is not too close to secondary ignition wires or coils, solenoids, relays or any motors. Repair as necessary. After repairs, go to step 9 . If no problem is found, go to step 6 .
5. Turn ignition off. Check for an intermittent and for a poor connection at the MAF sensor. Repair as necessary. After repairs, go to step 9 . If no problem is found, go to step 7 .
6. Check for an intermittent or poor connection at PCM. Repair as necessary. After repairs, go to step 9 . If no problem is found, go to step 8 .
7. Replace MAF sensor. After replacing sensor, go to step 9 .
8. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
9. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
10. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Any water that enters the air intake system and reaches the MAF sensor could cause this DTC to set. Water rapidly cools the hot sensing elements in the sensor causing a false indication of excessive airflow. Check for evidence of water intrusion. A poor connection in the ignition 1 voltage circuit of MAF sensor can cause DTC to set.

DTC P0106: MANIFOLD ABSOLUTE PRESSURE SYSTEM PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS article.

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

PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit. PCM also provides ground on the low reference circuit. The MAP sensor provides a signal to PCM on the signal circuit which is relative to pressure changes in the manifold. PCM should detect a low signal voltage at a low MAP, such as during idle or deceleration. PCM should detect a high signal voltage at high MAP, such as ignition on, with engine off or at a Wide Open Throttle (WOT) condition.

Certain models will also use MAP sensor in order to determine the Barometric Pressure (BARO). This occurs when ignition switch is turned on, with engine off. The BARO reading may also be updated whenever engine is operated at WOT. The PCM monitors MAP sensor signal for voltage outside of the normal range.

PCM calculates a predicted value for the MAP sensor based on throttle position and engine speed. PCM then compares the predicted value to the actual MAP sensor signal. DTC will set if MAP sensor signal is not within the predicted range.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0401, P0404, P0405, P0410, P0440, P0442, P0443 or P0446 is not set
2. Engine is running.
3. Engine speed is 400-5000 RPM.
4. Change in engine speed is less than 100 RPM.
5. Traction control is not active.
6. Throttle position is zero to 100 percent.
7. Change in idle air is less than 10 grams/second.
8. Change in EGR position is less than 20 percent.
9. A/C compressor clutch is steady.
10. Power steering is stable.
11. Power Take-Off (PTO) is not active (if equipped).
12. Brake and clutch switch state does not change.
13. All conditions are stable for 2 seconds.

Conditions for setting DTC

1. Actual MAP sensor signal is not within the predicted range for 1.5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe the throttle angle parameter. Move the throttle slowly from closed to wide open position. If throttle angle moves steadily and completely from zero to greater than 98 percent, go to next step. If throttle angle does not move steadily and completely from zero to greater than 98 percent, go to «DTC P0121»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0121-throttle-position-sensor-performance).
3. Compare MAP sensor value to BARO value in a known-good vehicle. Obtain the local weather service barometer reading (in. Hg). Multiply reading by 3.4. The result indicates the correct BARO value in kPa for your area. If MAP value normal for the altitude, go to next step. If MAP value is not normal for the altitude, go to step 8.
4. Observe MAP sensor kPa display on scan tool. Start engine. If MAP sensor changes value, go to next step. If MAP sensor does not change value, go to step 8.
5. Turn ignition off. Disconnect vacuum hose from MAP sensor. Leave harness connected. Connect a hand-held vacuum pump to MAP sensor. Turn ignition on, with engine off. Observe MAP sensor value as vacuum is slowly applied at one in. Hg at a time. Each inch of vacuum should result in a 3-4 kPa drop in MAP sensor value. Observe MAP sensor value or display for a skip or a jump while increasing vacuum up to 20 in. Hg. If scan tool indicates a skip or a jump in value, go to step 16. If scan tool does not indicate a skip or jump in value, go to next step.
6. Observe MAP sensor value with 20 in. Hg applied to MAP sensor. If scan tool indicates that MAP sensor value is less than 34 kPa, go to next step. If scan tool does not indicate that MAP sensor value is less than 34 kPa, go to step 8.
7. Disconnect hand-held vacuum pump. MAP sensor value should return to value observed in step 3. If MAP sensor value returns to original value observed in step 3, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If MAP sensor value does not return to original value observed in step 3, go to step 16.
8. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on, with engine off. If scan tool indicates that MAP sensor voltage is greater than 0.1 volt, go to step 15. If scan tool does not indicate that MAP sensor voltage is not greater than 0.1 volt, go to next step.
9. Connect a fused jumper wire between MAP sensor harness connector terminals "B" (Light Green wire) and "C" (Gray wire). (Scheme 3) If scan tool indicates that MAP sensor voltage is about 5 volts, go to next step. If scan tool does not indicate that MAP sensor voltage is about 5 volts, go to step 14.
10. Remove jumper wire. Check voltage between a known-good ground and MAP sensor harness connector terminal "C" (Gray wire). If voltage reading is greater than 5.2 volts, go to step 12. If voltage reading is not greater than 5.2 volts, go to next step.
11. Using a test light connected to battery voltage, probe MAP sensor harness connector terminal "A" (Orange/Black wire on "L" and "M" Series; Orange wire on "S" and "T" Series). If test light illuminates, go to step 16. If test light does not illuminate, go to step 13.
12. Turn ignition off. Check for short to voltage in Gray wire. Repair as necessary. After repairs, go to step 20. If circuit is okay, go to step 17.
13. Turn ignition off. Check for high resistance or open in Orange/Black wire ("M" and "L" Series) or Orange wire ("S" and "T" Series). Repair as necessary. After repairs, go to step 20. If circuit is okay, go to step 17.
14. Turn ignition off. Check for high resistance in Gray wire or Light Green wire. Repair as necessary. After repairs, go to step 20. If circuit(s) are okay, go to step 17.
15. Turn ignition off. Check for short to voltage in Light Green wire. Repair as necessary. After repairs, go to step 20. If circuit is okay, go to step 17.
16. Turn ignition off. Check MAP sensor for poor connections. Repair as necessary. After repairs, go to step 20. If connections are okay, go to step 18.
17. Check PCM for poor connections. Repair as necessary. After repairs, go to step 20. If connections are okay, go to step 19.
18. Replace MAP sensor. After replacing sensor, go to step 20.
19. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
20. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
21. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check MAP sensor vacuum source for leaks, restrictions or faulty connections. Ensure vacuum source only supplies MAP sensor and not other systems such as cruise control, auxiliary vacuum gauges, etc.

DTC P0107: MANIFOLD ABSOLUTE PRESSURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

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

PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit. PCM also provides ground on the low reference circuit. The MAP sensor provides signal to PCM on the signal circuit which is relative to the pressure changes in the manifold. PCM should detect a low signal voltage at a low MAP, such as during idle or deceleration. PCM should detect a high signal voltage at a high MAP, such as ignition on, with engine off, or at Wide Open Throttle (WOT) condition.

Certain models will also use the MAP sensor in order to determine the Barometric Pressure (BARO). This occurs when ignition is on, with engine off. The BARO reading may also be updated whenever engine is operated at WOT. PCM monitors the MAP sensor signal for voltage outside of the normal range. If PCM detects a MAP sensor signal voltage that is excessively low, DTC will set.

Conditions for running DTC

1. Ignition is on.
2. DTCs P0121, P0122 or P0123 is not set
3. Throttle angle is greater than zero percent when engine speed is less than 800 RPM.
4. Throttle angle is greater than 12.5 percent when engine speed is greater than 800 RPM.

Conditions for setting DTC

1. MAP sensor voltage is less than 0.10 volt for more than 2 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, monitor DTC information. If scan tool indicates that DTC P1635 is current, go to «DTC P1635»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p1635-5-volt-reference-1-circuit). If scan tool does not indicate that DTC P1635 is current, go to next step.
3. Using scan tool, observe the MAP 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.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
5. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on, with engine off. Check voltage between a known-good ground and MAP sensor harness connector terminal "C" (Gray wire). (Scheme 3) If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 7.
6. Connect a fused jumper wire MAP sensor harness connector terminals "B" (Light Green wire) and "C" (Gray wire). If scan tool indicates that voltage is about 5 volts, go to step 9. If scan tool does not indicate that voltage is not about 5 volts, go to step 8.
7. Turn ignition off. Check for short to ground or open in Gray wire. Repair as necessary. After repairs, go to step 13. If circuit is okay, go to step 10.
8. Turn ignition off. Check for short to ground or open in Light Green wire. Repair as necessary. After repairs, go to step 13. If circuit is okay, go to step 10.
9. Turn ignition off. Check for poor connections at MAP sensor. Repair as necessary. After repairs, go to step 13. If connections are okay, go to step 11.
10. Check for poor connections at PCM. Repair as necessary. After repairs, go to step 13. If connections are okay, go to step 12.
11. Replace MAP sensor. After replacing sensor, go to step 13.
12. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
13. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
14. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check MAP sensor vacuum source for leaks, restrictions, or poor connections.

DTC P0108: MANIFOLD ABSOLUTE PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

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

PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit. PCM also provides ground on the low reference circuit. The MAP sensor provides a signal to PCM on the signal circuit which is relative to the pressure changes in the manifold. PCM should detect a low signal voltage at a low MAP, such as during idle or deceleration. PCM should detect a high signal voltage at a high MAP, such as ignition on, with engine off, or at Wide Open Throttle (WOT) condition.

Certain models will also use the MAP sensor in order to determine the Barometric Pressure (BARO). This occurs when ignition switch on, with engine off. The BARO reading may also be updated whenever engine is operated at WOT. The PCM monitors MAP sensor signal for voltage outside of the normal range. If PCM detects a MAP sensor signal voltage that is excessively high, DTC will set.

Conditions for running DTC

1. Engine has been running for a time that is determined by the start-up coolant temperature. The time ranges from 2 minutes at less than 22°F (30°C) to one second at greater than 86°F (30°C).
2. DTCs P0121, P0122 or P0123 is not set
3. Throttle angle is zero percent when engine speed is less than 1200 RPM.
4. Throttle angle is less than 20 percent when engine speed is greater than 1200 RPM.

Conditions for setting DTC

1. MAP sensor voltage is greater than 4.9 volts for more than 2 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, monitor DTC information. If scan tool indicates that DTC P1635 also set, go to «DTC P1635»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p1635-5-volt-reference-1-circuit) . If scan tool does not indicate that DTC P1635 is also set, go to next step.
3. Allow engine to idle. If scan tool indicates that MAP sensor voltage is greater than 4.9 volts, go to step 5 . If scan tool does not indicate that MAP sensor voltage is greater than 4.9 volts, go to next step.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on, with engine off. If scan tool indicates that MAP sensor voltage is less than 0.1 volt, go to next step. If scan tool does not indicate that MAP sensor voltage is less than 0.1 volt, go to step 8 .
6. Check voltage between ground and MAP sensor harness connector terminal "A" (Orange/Black wire on "L" and "M" Series or Orange wire on "S" and "T" Series). If voltage reading is 4.7-5.2 volts, go to step 11 . If voltage reading is not 4.7-5.2 volts, go to next step.
7. If voltage reading is greater than 5.2 volts, go to step 10 . If voltage reading is not greater than 5.2 volts, go to step 9 .
8. Turn ignition off. Check for short to voltage in Light Green wire. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 12 .
9. Turn ignition off. Check for open in Orange/Black wire ("L" and "M" Series) or Orange wire ("S" and "T" Series). Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 12 .
10. Turn ignition off. Check for short to voltage in Gray wire. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 12 .
11. Turn ignition off. Check for poor connections at MAP sensor. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to step 13 .
12. Check for poor connections at PCM. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to step 14 .
13. Replace MAP sensor. After replacing sensor, go to step 15 .
14. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
15. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
16. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check MAP sensor vacuum source for leaks, restrictions or for poor connections.

DTC P0112: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Intake Air Temperature (IAT) sensor is a thermistor located in fresh air duct to throttle body. IAT sensor measures temperature of the air entering engine. The PCM supplies 5 volts to IAT signal circuit. When IAT sensor is cold, sensor resistance is high. When air temperature increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on IAT signal circuit. With lower sensor resistance, PCM detects a lower voltage on IAT signal circuit. If PCM detects an excessively low IAT signal voltage, indicating a high temperature, this DTC will set.

Conditions for running DTC

1. DTC P0502 or P0503 is not set.
2. Engine run time is greater than 45 seconds.
3. VSS indicates that vehicle speed is greater than 25 MPH.

Conditions for setting DTC

1. Intake air temperature is greater than 262°F (128°C) for 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe IAT sensor temperature. If IAT sensor temperature is greater than 262°F (128°C), go to step 4 . If IAT sensor temperature is not greater than 262°F (128°C), go to next step.
3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Turn ignition off. Disconnect IAT sensor harness connector. Turn ignition on, with engine off. Observe IAT sensor temperature on scan tool. If IAT sensor temperature is less than -38°F (-39°C), go to step 6 . If IAT sensor temperature is not less than -38°F (-39°C), go to next step.
5. Turn ignition off. Check Tan wire at IAT sensor for short to ground or short to Black wire at IAT sensor. Repair as necessary. After repairs, go to step 9 . If circuits are okay, go to step 7 .
6. Turn ignition off. Replace IAT sensor. After replacing sensor, go to step 9 .
7. Disconnect PCM harness connector. Check for poor connection at PCM harness connector. Repair as necessary. After repairs, go to step 9 . If connections are okay, go to next step.
8. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
9. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
10. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

When vehicle is at ambient temperature, intake air temperature sensor and engine coolant temperature sensor temperatures should be relatively close to each other. See appropriate SENSOR OPERATING RANGE CHARTS article.

DTC P0113: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Intake Air Temperature (IAT) sensor is a thermistor located in fresh air duct to throttle body. IAT sensor measures temperature of air entering the engine. PCM supplies 5 volts to IAT signal circuit. When IAT sensor is cold, sensor resistance is high. When air temperature increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on IAT signal circuit. With lower sensor resistance, PCM detects a lower voltage on IAT signal circuit. If PCM detects an excessively high IAT signal voltage, indicating a low temperature, this DTC will set.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0125, P0128, P0502 or P0503 is not set.
2. Engine run time is more than 120 seconds.
3. VSS indicates that vehicle speed is less than 7 MPH.
4. Engine coolant temperature is greater than 140°F (60°C).
5. Mass airflow is less than 15 grams/second.

Conditions for setting DTC

1. IAT sensor signal voltage indicates that intake air temperature is less than -38°F (-39°C) for more than 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe IAT sensor temperature. If IAT sensor temperature is less than -36°F (-38°C), go to step 4 . If IAT sensor temperature is not less than -36°F (-38°C), go to next step.
3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Turn ignition off. Disconnect IAT sensor harness connector. Connect a DVOM between IAT sensor harness connector terminals. Turn ignition on. If voltage reading is greater than 5 volts, go to next step. If voltage reading is not greater than 5 volts, go to step 6 .
5. Turn ignition off. Check for short to voltage in Tan wire between IAT sensor and PCM. Repair as necessary. After repairs, go to step 14 . If circuit is okay, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
6. Turn ignition off. Connect a fused jumper wire between IAT sensor harness connector terminals. Turn ignition on, with engine off. Observe IAT sensor temperature on scan tool. If IAT sensor temperature is greater than 262°F (128°C), go to step 10 . If IAT sensor temperature is not greater than 262°F (128°C), go to next step.
7. Turn ignition off. Connect a fused jumper wire between a known-good ground and IAT sensor harness connector terminal "B" (Tan wire). Turn ignition on, with engine off. Observe IAT sensor temperature on scan tool. If IAT sensor temperature is greater than 262°F (128°C), go to step 9 . If IAT sensor temperature is not greater than 262°F (128°C), go to next step.
8. Turn ignition off. Check for open circuit or high resistance in Tan wire. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 11 .
9. Turn ignition off. Check for high resistance or open in Black wire between IAT sensor and PCM. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 11 .
10. Turn ignition off. Check for poor connections at IAT sensor harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 12 .
11. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 13 .
12. Replace IAT sensor. After replacing sensor, go to step 14 .
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
15. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

When vehicle is at ambient temperature, IAT sensor and engine coolant temperature sensor temperatures should be relatively close to each other. See appropriate SENSOR OPERATING RANGE CHARTS article.

If a short to a separate 5-volt source occurs, this DTC may set. If this condition exists, a continuity test to all other PCM 5-volt reference circuits will be necessary.

DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. The PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively low ECT signal voltage, which is a high temperature indication, this DTC will set.

Conditions for running DTC

1. Engine run time is more than 10 seconds.

Conditions for setting DTC

1. engine coolant temperature sensor temperature is greater than 282°F (139°C) for more than 20 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe engine coolant temperature sensor temperature display. If scan tool indicates that engine coolant temperature sensor temperature is greater than 282°F (139°C), go to step 4. If scan tool does not indicate that engine coolant temperature sensor temperature is greater than 282°F (139°C), go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect ECT sensor harness connector. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is less than -36°F (-38°C), go to step 6. If scan tool does not indicate that ECT sensor temperature is less than -36°F (-38°C), go to next step.
5. Turn ignition off. Disconnect PCM harness connector C1. Check for short to ground in Yellow wire between ECT sensor and PCM harness connector C1 terminal No. 74 or check for short in Yellow wire to other reference low circuits. (Scheme 2) Repair as necessary. After repairs, go to step 8. If circuit is okay, go to step 7.
6. Turn ignition off. Replace ECT sensor. After replacing sensor, go to step 8.
7. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
8. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
9. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

An overheating condition may cause this DTC to set. After starting engine, ECT should rise steadily to about 194°F (90°C) then stabilize when thermostat opens.

Test ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability concerns. See appropriate SENSOR OPERATING RANGE CHARTS article.

DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. The PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively high ECT signal voltage, which is a low temperature indication, this DTC will set.

Conditions for running DTC

1. Engine has been running for more than 60 seconds.

Conditions for setting DTC

1. ECT sensor temperature is less than -36°F (-38°C) for 20 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is less than -36°F (-38°C), go to step 4 . If scan tool does not indicate that ECT sensor temperature is less than -36°F (-38°C), go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Turn ignition off. Disconnect ECT sensor harness connector. Connect a fused jumper wire ECT sensor harness connector terminals. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280°F (138°C), go to step 7 . If scan tool does not indicate that ECT sensor temperature is greater than 280°F (138°C), go to next step.
5. Turn ignition off. Connect a fused jumper wire between a known-good ground and ECT sensor harness connector terminal "B" (Yellow wire). Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280°F (138°C), go to step 7 . If scan tool does not indicate that ECT sensor temperature is greater than 280°F (138°C), go to next step.
6. Turn ignition off. Check for short to voltage, high resistance or open in Yellow wire between ECT sensor and PCM. Repair as necessary. After repairs, go to step 12 . If circuit is okay, go to next step.
7. Turn ignition off. Check for high resistance or open in Black wire between ECT sensor and PCM. Repair as necessary. After repairs, go to step 12 . If circuit is okay, go to step 9 .
8. Check for poor connections at ECT sensor harness connector. Repair connections as necessary. After repairs, go to step 12 . If connections are okay, go to step 10 .
9. Check for poor connections at PCM harness connector. Repair connections as necessary. After repairs, go to step 12 . If connections are okay, go to step 11 .
10. Replace ECT sensor. After replacing sensor, go to step 12 .
11. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
13. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

If a short to a separate 5-volt source occurs, this DTC may set. If this condition exists, test to all other PCM circuits to diagnose the specific circuit. After starting engine, the ECT should rise steadily to about 194°F (90°C), then stabilize when thermostat opens.

Check ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. See appropriate SENSOR OPERATING RANGE CHARTS article. A skewed sensor could result in poor driveability concerns. If a malfunction is not present at this time, refer to DTC P1115 .

DTC P0121: THROTTLE POSITION SENSOR PERFORMANCE

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 4

Throttle Position (TP) sensor is used by PCM to determine throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit. PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to Wide Open Throttle (WOT) position provides PCM with a signal voltage from less than one volt to greater than 4 volts through the TP sensor signal circuit.

When the conditions for running this DTC are met, PCM will use the MAP sensor in order to determine if the predicted operating range of the TP sensor is correct. A skewed MAP sensor may cause this DTC to set. The MAP sensor should be tested for proper operation if TP sensor is operating properly and this DTC continues to set.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0122, P0123, P0506, P0507, P1106, P1107, P1121 or P1122 is not set
2. Engine is running for more than 2 minutes.
3. Engine coolant temperature is greater than 158°F (70°C).
4. MAP is less than 43 kPa for a TP sensor skewed high test.
5. MAP is greater than 67 kPa for a TP sensor skewed low test.
6. MAP is steady for 2 seconds or more.
7. TP does not varying greater than 1.5 percent for 2 seconds or more.

Conditions for setting DTC

1. TP sensor reading is greater than a predicted value when the MAP is less than 43 kPa.
2. TP sensor reading is less than a predicted value when the MAP is greater than 67 kPa.
3. Conditions are present for one second.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe TP sensor angle parameter while slowly opening the throttle to WOT. If TP angle increases steadily and evenly from the closed throttle value of zero percent to WOT throttle value of greater than 98 percent, go to next step. If TP angle does not increase steadily and evenly from the closed throttle value of zero percent to WOT throttle value of greater than 98 percent, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC or as closely as possible to FREEZE FRAME/FAILURE RECORDS conditions. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on, with engine off. Using scan tool, observe TP sensor voltage parameter. If voltage parameter is zero volts, go to next step. If voltage parameter is not zero volts, go to step 6.
5. Turn ignition off. Connect a fused jumper between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series; Gray wire on "S" and "T" Series) and "C" (Dark Blue wire). (Scheme 4) Turn ignition on, with engine off. Using scan tool, observe TP sensor voltage parameter. If voltage parameter is 5 volts, go to step 9. If voltage parameter is not 5 volts, go to step 7.
6. Turn ignition off. Using a DVOM, check Dark Blue wire for short to voltage. Repair as necessary. After repairs, go to step 14. If circuit is okay, go to step 12.
7. Turn ignition off. Using DVOM, check Gray wire for open or high resistance. Repair as necessary. After repairs, go to step 14. If circuit is okay, go to next step.
8. Check Dark Blue wire for open or high resistance. Repair as necessary. After repairs, go to step 14. If circuit is okay, go to step 11.
9. Turn ignition off. Check Black wire for open and high resistance. Repair as necessary. After repairs, go to step 14. If circuit is okay, go to next step.
10. Check for a faulty connection at TP sensor harness connector. Repair as necessary. After repairs, go to step 14. If connection is okay, go to step 12.
11. Check for a faulty connection at PCM harness connector. 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. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC test runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool, observe the stored information and Capture info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check for a skewed MAP sensor. A skewed MAP signal may cause PCM to incorrectly determine that TP sensor is out of range. Check for an unusually low or unusually high MAP reading. If DTC is intermittent or TP sensor system is still suspect, go to DTC P1121 . If DTC is intermittent, see appropriate TROUBLE SHOOTING - NO CODES article.

DTC P0122: THROTTLE POSITION SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

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

DTC will run when ignition is on and DTC will set when TP sensor signal voltage is less than 0.1 volt for more than 2 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe TP sensor voltage parameter. If voltage parameter is less than 0.1 volt, go to step 4. If voltage parameter is not less than 0.1 volt, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC or as close as possible to FREEZE FRAME/FAILURE RECORDS conditions. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, go to step 10.
4. Turn ignition off. Disconnect TP sensor harness connector. Connect a fused jumper between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series) and "C" (Dark Blue wire). (Scheme 4) Turn ignition on, with engine off. Using scan tool, observe TP sensor voltage parameter. If voltage parameter is 5 volts, go to step 11. If voltage parameter is not 5 volts, go to next step.
5. Remove jumper wire. Using a DVOM, check voltage between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series) and "B" (Black wire). If voltage reading is about 5 volts, go to step 9. If voltage reading is not about 5 volts, go to next step.
6. Turn ignition off. Using DVOM, check for open or high resistance in Black wire ("L" and "M" Series) or Gray wire ("S" and "T" Series). Repair as necessary. After repairs, go to step 14. If circuit is okay, go to next step.
7. Check all of the 5-volt reference circuits from PCM for a short to ground. See WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 14. If circuits are okay, go to next step.
8. Connect DVOM between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series) and "B" (Black wire). (Scheme 4) Observe voltage display on DVOM while disconnecting all of the sensors that use a 5-volt reference signal, one at a time. A change in voltage indicates a faulty component. Repair as necessary. After repairs, go to step 14. If no problem is found, go to step 10.
9. Turn ignition off. Using DVOM, check for open, high resistance, or short to ground in Dark Blue wire. Repair as necessary. After repairs, go to step 14. If circuit is okay, go to next step.
10. Turn ignition off. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 14. If connections are okay, go to step 13.
11. Turn ignition off. Check for poor connections at TP sensor harness connector. Repair as necessary. After repairs, go to step 14. If connections are okay, go to next step.
12. Replace TP sensor. After replacing sensor, go to step 14.
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC test runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0123: THROTTLE POSITION SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 5

Throttle Position (TP) sensor is used by PCM to determine throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit. PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to WOT position provides PCM with a signal voltage from less than one volt to greater than 4 volts through the TP sensor signal circuit. If PCM detects an excessively high signal voltage, this DTC will set.

Conditions for running DTC

1. Ignition is on.
2. DTC P1635 or P1639 is not set.

Conditions for setting DTC

1. TP sensor signal voltage is greater than 4.9 volts for more than one second.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe TP sensor voltage parameter with throttle closed. If voltage is greater than 4.9 volts, go to step 4. If voltage is not greater than 4.9 volts, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC or as closely as possible to FREEZE FRAME/FAILURE RECORDS conditions. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, go to «DTC P1122»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p1122-throttle-position-sensor-circuit).
4. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on, with engine off. Using scan tool, observe TP sensor voltage parameter. If voltage parameter is zero volts, go to next step. If voltage parameter is not zero volts, go to step 8.
5. Using DVOM, check voltage in TP sensor harness connector terminal "A" (Black wire on "L" and "M" Series; Gray wire on "S" and "T" Series). (Scheme 4) If voltage reading is 5 volts, go to next step. If voltage reading is not 5 volts, go to step 9.
6. Connect a test light between battery voltage and TP sensor harness connector terminal "B" (Black wire). If test light illuminates, go to step 10. If test light does not illuminate, go to next step.
7. Turn ignition off. Check for high resistance or open in Black wire between TP sensor harness connector terminal "B" and PCM harness connector C1 terminal No. 60. (Scheme 2)or (Scheme 4). Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 12.
8. Check for short to voltage in Dark Blue wire between TP sensor harness connector terminal "C" and PCM harness connector C2 terminal No. 24. (Scheme 2) Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 12.
9. Turn ignition off. Check all of the 5-volt reference circuits for short to voltage. See WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 18. If circuits are okay, go to next step.
10. Connect DVOM between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series) and "B" (Black wire). (Scheme 4) Using scan tool, command EGR valve to 100 percent while observing DVOM. If voltage changes while commanding the EGR, go to next step. If voltage does not change while commanding the EGR, go to step 14.
11. Disconnect EGR valve harness connector. With DVOM still connected, observe voltage while commanding the EGR to 100 percent. If voltage changes while commanding the EGR, go to step 13. If voltage does change while commanding the EGR, go to next step.
12. Turn ignition off. Replace EGR valve. After replacing EGR valve, go to step 17.
13. Turn ignition off. Repair short in circuits between EGR valve harness connector terminals "A" (White wire) and "D" (Gray wire). (Scheme 5) After repairs, go to step 18.
14. Turn ignition off. Check for faulty connections at TP sensor harness connector. Repair as necessary. After repairs, go to step 18. If connections are okay, go to step 16.
15. Check for faulty connections at PCM harness connector. Repair as necessary. After repairs, go to step 18. If connections are okay, go to step 17.
16. Replace TP sensor. After replacing sensor, go to step 18.
17. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
18. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC test runs and passes, go to next step. If DTC resets, go to step 2.
19. Using scan tool, observe the Stored Information and Stored Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0125: ENGINE COOLANT TEMPERATURE EXCESSIVE TIME TO ENTER CLOSED LOOP FUEL CONTROL

Note. For circuit reference, see WIRING DIAGRAMS article.

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

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

This DTC will only run once per ignition cycle within the enabling conditions and will set when there has been excessive time to reach a minimum coolant temperature required for closed-loop fuel control.

Conditions for running DTC

1. DTCs P0100, P0101, P0103, P0110, P0111, P0112, P0113, P0117, P0118, P0125, P0500, P0501, P0503, P1114 or P1115 is not set
2. Minimum air intake temperature is 19°F (-7°C) or greater.
3. Start-up coolant temperature is less than 104°F (40°C).
4. Engine running more than 2 minutes, but less than 17 minutes.
5. Vehicle speed is greater than 5 MPH for more than 0.5 miles.
6. MAF average reading is more than 15 grams/second.

Conditions for setting DTC

1. Closed-loop coolant temperature of 104°F (40°C) is not reached within a predetermined time.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. If cooling system is low on coolant, add coolant or diagnose coolant loss. After repairs, go to next step.
3. Turn ignition off. Disconnect ECT sensor harness connector. Connect a fused jumper wire between ECT sensor harness connector terminals. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280°F (138°C), go to step 7. If scan tool does not indicate that ECT sensor temperature is greater than 280°F (138°C), go to next step.
4. Turn ignition off. Disconnect ECT sensor harness connector. Connect a fused jumper wire between a known-good ground and ECT sensor harness connector terminal "B" (Yellow wire). Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280°F (138°C), go to next step. If scan tool does not indicate that ECT sensor temperature is greater than 280°F (138°C), go to step 6.
5. Turn ignition off. Repair high resistance or open in Black wire between ECT sensor and PCM harness connector C1 terminal 80. (Scheme 2) After repairs, go to step 10.
6. Turn ignition off. Repair high resistance or open in Yellow wire between ECT sensor and PCM harness connector C1 terminal No. 74. (Scheme 2) After repairs, go to step 10.
7. Turn ignition off. Remove ECT sensor. Suspend ECT sensor and a thermometer in a pan of water. Place pan on a burner or hot plate. Check ECT sensor resistance through the specified range of temperatures. See appropriate SENSOR OPERATING RANGE charts. If temperature ranges are as specified, go to next step. If temperature ranges are not as specified, go to step 9.
8. Reinstall ECT sensor. After reinstalling sensor, diagnose engine cooling system.
9. Replace ECT sensor. After replacing sensor, go to next step.
10. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTC are displayed, system is okay.

DTC P0128: ENGINE COOLANT TEMPERATURE EXCEEDS LENGTH OF TIME TO REACH PRESET TEMPERATURE

Note. For circuit reference, see WIRING DIAGRAMS article.

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

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

This DTC will only run once per ignition cycle within the enabling conditions. If engine coolant fails to reach a preset target temperature before a calculated airflow is accumulated, DTC will set.

Conditions for running DTC

1. DTCs P0100, P0101, P0103, P0110, P0111, P0112, P0113, P0117, P0118, P0125, P0500, P0501, P0503, P1114 or P1115 is not set
2. Coolant temperature is less than 178°F (81°C).
3. Air intake temperature is 19°F (-7°C) or greater.
4. Engine running for more than 2 minutes, but less than 17 minutes.
5. Vehicle speed is greater than 5 MPH for more than 0.5 miles.
6. MAF average reading is more than 13 grams/second.

Conditions for setting DTC

1. The length of time for engine coolant to reach a preset temperature has been exceeded.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. If cooling system is low on coolant, add coolant or diagnose coolant loss. After repairs, go to next step.
3. Turn ignition off. Disconnect ECT sensor harness connector. Connect a fused jumper wire ECT sensor harness connector terminals. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280°F (138°C), go to step 7 . If scan tool does not indicate that ECT sensor temperature is greater than 280°F (138°C), go to next step.
4. Turn ignition off. Disconnect ECT sensor harness connector. Connect fused jumper wire between a known-good ground and ECT sensor harness connector terminal "B" (Yellow wire). Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280°F (138°C), go to next step. If scan tool does not indicate that ECT sensor temperature is greater than 280°F (138°C), go to step 6 .
5. Turn ignition off. Repair Yellow wire for short to ground or short to Black wire in ECT sensor harness connector circuit. After repairs, go to step 10 .
6. Turn ignition off. Repair Black wire for high resistance or open circuit. After repairs, go to step 10 .
7. Turn ignition off. Remove ECT sensor. Suspend ECT sensor and a thermometer in a pan of water. Place pan on a burner or hot plate. Check ECT sensor resistance through the specified range of temperatures. See appropriate SENSOR OPERATING RANGE CHARTS article. If temperature ranges are as specified, go to next step. If temperature ranges are not as specified, go to step 9 .
8. Reinstall ECT sensor. After reinstalling sensor, diagnose engine cooling.
9. Replace ECT sensor. After replacing sensor, go to next step.
10. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0131 OR P0151: HEATED OXYGEN SENSOR VOLTAGE LOW ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 6

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

DTC is designed to detect an HO2S voltage that remains at a low voltage for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System operating in closed-loop.
5. Ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress
8. Scan tool output controls are not active.

Conditions for setting DTC

1. The HO2S voltage is less than 87 millivolts for 300 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Warm engine to normal operating temperature. Using scan tool, monitor HO2S voltage. If HO2S voltage is fixed at less than 86 millivolts, go to step 4. If HO2S voltage is not fixed at less than 86 millivolts, go to next step.
3. Turn ignition off. The condition that set this DTC is not present. This DTC may have been set by HO2S high signal wire intermittently shorted to engine ground or to HO2S low reference circuit, water intrusion into HO2S connector, or exhaust leak between HO2S and engine. DTC may also have been set by an intermittent lean engine condition such as, vacuum leak, incorrect or defective PCV or system, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, problem is intermittent.
4. Turn ignition off. Disconnect HO2S harness connector C1. Turn ignition on, with engine off. Using scan tool, monitor HO2S voltage. If HO2S voltage is 351-551 millivolts, go to next step. If HO2S voltage is not 351-551 millivolts, go to step 6.
5. Turn ignition off. The HO2S may be detecting a lean exhaust condition. Check for water intrusion in HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, lean fuel injectors or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, go to step 8.
6. Turn ignition off. Disconnect PCM connector C1. Using a DVOM, check resistance between ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). (Scheme 6) Check resistance between HO2S harness connector terminals "A" (Tan/White or Tan wire) and "B" (Purple/White or Purple wire). If resistance is infinite on both circuits, go to step 9. If resistance is not infinite on both circuits, go to next step.
7. Repair Purple/White or Purple wire for short to ground or short to Tan/White or Tan wire in HO2S circuit. After repairs, go to step 10.
8. Replace HO2S. After replacing sensor, go to step 10.
9. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
10. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0131 OR P0151: HEATED OXYGEN SENSOR VOLTAGE LOW ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

DTC is designed to detect an HO2S voltage that remains at a low voltage for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System is operating in closed-loop.
5. Ignition 1 signal is 9-18 volts.
6. Fuel tank level is more than 10 percent.
7. Intrusive tests are not in progress.
8. Scan tool output controls are not active.

Conditions for setting DTC

1. The HO2S voltage is less than 87 millivolts for 300 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Allow engine to reach normal operating temperature. Using scan tool, observe HO2S voltage. If HO2S voltage is less than 87 millivolts, go to step 4. If HO2S voltage is not less than 87 millivolts, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
4. Turn ignition off. Disconnect appropriate HO2S connector. Connect a jumper wire between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6)or see scheme 7. Turn ignition on, with engine off. Observe HO2S voltage on scan tool. If HO2S voltage is 350-550 millivolts, go to next step. If HO2S voltage is not 350-550 millivolts, go to step 6.
5. Turn ignition off. The HO2S may be detecting a lean exhaust condition. Check for water intrusion in HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 12. If no problem is found, go to step 8.
6. Turn ignition off. Disconnect PCM connector C1. Check for short to ground in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 12. If circuit is okay, go to next step.
7. Check Purple/White or Purple wire for short to Tan/White or Tan wire in HO2S circuit. Repair as necessary. After repairs, go to step 12. If circuit is okay, go to step 9.
8. Turn ignition off. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 12. If connections are okay, go to step 10.
9. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 12. If connections are okay, go to step 11.
10. Replace affected HO2S. After replacing sensor, go to step 12.
11. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
13. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0132 OR P0152: HEATED OXYGEN SENSOR VOLTAGE HIGH ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains at a high voltage for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System operating in closed-loop status.
5. The ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress.
8. Scan tool output controls are not active.

Conditions for setting DTC

1. The HO2S voltage is greater than 977 millivolts for 250 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Warm engine to normal operating temperature. Using scan tool, monitor HO2S voltage. If HO2S voltage is fixed at greater than 976 millivolts, go to step 4. If HO2S voltage is not fixed at greater than 976 millivolts, go to next step.
3. Turn ignition off. The condition that set this DTC is not present. This DTC may have been set by a signal wire intermittently shorted to voltage, water intrusion in HO2S connector, silicone contaminated HO2S, intermittent rich engine condition, EVAP canister purge condition, engine oil contaminated by fuel, incorrect fuel pressure, leaking fuel pressure regulator, rich fuel injectors, inaccurate MAF sensor, or rich engine condition during DFCO operation. Repair as necessary. After repairs, go to step 10. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect HO2S harness connector. Turn ignition on, with engine off. Using scan tool, monitor HO2S voltage. If HO2S voltage is 351-551 millivolts, go to next step. If HO2S voltage is not 351-551 millivolts, go to step 6.
5. Turn ignition off. Check for water intrusion in HO2S connector, silicone contaminated HO2S, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, leaking fuel pressure regulator, rich fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, go to step 8.
6. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on, with engine off. Using a DVOM, check voltage between a known-good ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). (Scheme 6) If voltage is greater than 20 millivolts, go to next step. If voltage is not greater than 20 millivolts, go to step 9.
7. Turn ignition off. Repair short to voltage in Purple/White or Purple wire. After repairs, go to step 10.
8. Replace HO2S. After replacing sensor, go to step 10.
9. Turn ignition off. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
10. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Note. Never solder HO2S wires.

Check fuel pressure. If pressure is too high, system will run rich. The PCM can only compensate for some increase. Check for a rich or leaking injector. Check for fuel-contaminated oil, EVAP canister purge for fuel saturation, leaking fuel pressure regulator diaphragm, intermittent TP sensor output, or a false rich indication due to silicone contamination of HO2S. This DTC, accompanied by a lean driveability condition and a powdery White deposit on sensor, may indicate a false rich condition.

DTC P0132 OR P0152: HEATED OXYGEN SENSOR VOLTAGE HIGH ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains at a high voltage for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404, or P1441 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System operating in closed-loop.
5. The ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress
8. Scan tool output controls are not active.

Conditions for setting DTC

1. The HO2S voltage is greater than 977 millivolts for 250 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Warm engine to normal operating temperature. Using scan tool, observe HO2S voltage. If HO2S voltage is greater than 977 millivolts, go to step 4. If HO2S voltage is not greater than 977 millivolts, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect HO2S harness connector. Connect a jumper wire between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6)or see scheme 7. Turn ignition on, with engine off. Observe HO2S voltage on scan tool. If HO2S voltage is 350-550 millivolts, go to next step. If HO2S voltage is not 350-550 millivolts, go to step 6.
5. Turn ignition off. The HO2S may be detecting a rich exhaust condition or may be contaminated. Check for water intrusion in HO2S connector, silicone contamination of HO2S, engine oil contaminated by fuel, incorrect fuel pressure, rich fuel injectors, inaccurate MAF sensor, or EVAP canister purge condition. Repair as necessary. After repairs, go to step 11. If no problem is found, go to step 7.
6. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on with engine off. Check Purple/White or Purple wire for short to voltage. Repair as necessary. After repairs, go to step 11. If circuit is okay, go to step 8.
7. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 11. If connections are okay, go to step 9.
8. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 11. If connections are okay, go to step 10.
9. Replace affected HO2S. After replacing sensor, go to step 11.
10. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
11. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
12. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Note. Remove any debris from PCM connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure that gaskets are installed correctly to prevent water intrusion into PCM.

Check HO2S connections for evidence of water intrusion. Water present in connector causes the battery voltage supply to the heater to bleed over to signal circuit. Check fuel pressure, system goes rich if pressure is too high. PCM compensates for some increase. If fuel pressure is too high, a DTC may set.

Check for a rich or leaking injector, EVAP canister purge for fuel saturation, MAF sensor, HO2S wires (wires provide supply of oxygen), or TP sensor. An intermittent TP sensor output causes system to go rich, due to a false indication of engine accelerating.

DTC P0133 OR P0153: HEATED OXYGEN SENSOR - SLOW RESPONSE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S that is lazy or slow when switching from lean-to-rich or from rich-to-lean. DTC is set when the average transition time is too long.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0352, P0353, P0354, P0355, P0356, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1401 or P1441 is not set
2. Engine coolant temperature is greater than 135°F (57°C).
3. Engine run time is greater than 160 seconds.
4. Mass airflow is 15-55 grams/second.
5. Engine speed is 1100-3000 RPM.
6. Throttle position is greater than 5 percent.
7. System is operating in closed-loop.
8. Ignition 1 signal is 9-18 volts.
9. Fuel tank level remaining is more than 10 percent.
10. Scan tool output controls are not active.
11. Conditions are met for 100 seconds.

Conditions for setting DTC

1. The rich-to-lean and lean-to-rich average response time is greater than a calibrated value.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, check for DTCs. If any other HO2S related DTCs are set, go to step 4. If no other HO2S related DTCs are set, go to next step.
3. If any powertrain related DTCs are set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no other DTCs are set, go to step 5.
4. Turn ignition off. The HO2S sensors have been contaminated. Replace affected HO2S sensors. Repair cause of contamination source prior to operating engine with replacement sensor. After repairs, go to step 18.
5. Using scan tool, clear DTCs. Reset fuel trim values. Start and operate engine at idle until engine reaches normal operating temperature. Operate engine within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and fails this ignition cycle, go to step 7. If DTC does not run this ignition cycle, go to next step.
6. Turn ignition off. The condition that set this DTC is not present. This DTC may have been set by exhaust system leak between engine and HO2S, poor HO2S connector terminal contact, water intrusion in HO2S connector, improperly torqued HO2S, inoperative HO2S heater, or poor PCM connector terminal contact. Check HO2S high or low circuit for an intermittent open or short, excessive circuit resistance of greater than 5 ohms, contaminated HO2S, or excessive engine oil or coolant consumption. Repair as necessary. After repairs, go to step 18. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
7. Turn ignition off. Check exhaust system for leaks between HO2S and engine. Check HO2S and PCM connectors for proper terminal contact. Repair as necessary. After repairs, go to step 18. If no problem is found, go to next step.
8. Disconnect HO2S harness connector. Connect jumper wire between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6) Turn ignition on, with engine off. Using a scan tool, monitor HO2S voltage. If HO2S voltage is 351-551 millivolts, go to next step. If HO2S voltage is not 351-551 millivolts, go to step 13.
9. Connect jumper wire between a known-good ground and HO2S harness connector terminal "B" Purple/White or Purple wire). Using scan tool monitor HO2S voltage. If HO2S voltage is less than 20 millivolts, go to next step. If HO2S voltage is not less than 20 millivolts, go to step 14.
10. Disconnect jumper wire. Connect a test light between a known-good ground and HO2S harness connector terminal "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 15.
11. Connect test light between HO2S harness connector terminals "C" (Black wire) and D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 16.
12. Turn ignition off. Check for contamination sources which may have caused HO2S to fail. Check for improper use of RTV sealant, contaminated fuel supply or excessive engine oil or coolant consumption. Repair as necessary. After repairs, go to step 17.
13. Turn ignition off. Repair short to voltage source between HO2S circuits. After repairs, go to step 18.
14. Turn ignition off. Check for open or high resistance in Tan/White, Tan, Purple/White or Purple wires in HO2S circuit. Repair as necessary. After repairs, go to step 18.
15. Turn ignition off. Repair Pink wire between HO2S and underhood fuse block. After repairs, go to step 18.
16. Turn ignition off. Repair Black wire between HO2S and ground. After repairs, go to step 18.
17. Replace HO2S. After replacing sensor, go to next step.
18. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
19. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Note. Never solder the HO2S wires

Check for an improperly installed air cleaner outlet duct, collapsed or restricted air cleaner outlet duct or a missing or plugged air filter, any vacuum leaks in throttle body or intake manifold. Check for damaged or blocked throttle body inlet, corrosion or leaks in exhaust system, or loose or missing exhaust hardware. Ensure HO2S is installed securely and pigtail harness is not contacting exhaust manifold or wires. Check for any HO2S contamination, vacuum hoses for splits, kinks and proper connections. Check for any excessive water, alcohol or other contaminants in fuel. Ensure PCM sensor grounds are clean, tight and properly positioned.

DTC P0133 OR P0153: HEATED OXYGEN SENSOR - SLOW RESPONSE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S that is lazy or slow when switching from lean-to-rich or from rich-to-lean. DTC is set when the average transition time is too long.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine coolant temperature is greater than 135°F (57°C).
3. Engine run time is greater than 160 seconds.
4. Mass airflow is 15-55 grams/second.
5. Engine speed is 1100-3000 RPM.
6. Throttle position is greater than 5 percent.
7. System operating in closed-loop.
8. Ignition 1 signal is 9-18 volts.
9. Fuel tank level remaining is more than 10 percent.
10. Scan tool output controls are not active.
11. Conditions are met for 100 seconds.

Conditions for setting DTC

1. The rich-to-lean and lean-to-rich average response time is greater than a calibrated value.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Operate engine at idle and warm to normal operating temperature. Operate vehicle within the parameters specified in conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Using scan tool, monitor the DTC information. If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
3. If both DTC P0133 and P0153 fails this ignition cycle, go to step 8. If only P0133 or P0153 fails this ignition cycle, go to next step.
4. Turn ignition off. Check for an exhaust system leak. Repair as necessary. After repairs, go to step 14. If no problem is found, go to next step.
5. Ensure appropriate HO2S is securely installed. Check for corrosion on terminals. Check terminal tension at HO2S and PCM or damaged wiring. Repair as necessary. After repairs, go to step 14. If no problem is found, go to next step.
6. Disconnect appropriate HO2S harness connector. Connect a jumper wire between a known-good wire and HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6)or see scheme 7. Turn ignition on, with engine off. Using scan tool, monitor HO2S voltage on the Engine 1 Data List. If scan tool indicates 350-550 millivolts, go to next step. If scan tool does not indicate 350-550 millivolts, go to step 10.
7. Connect jumper wires between battery ground and HO2S harness connector terminals "A" (Tan/White or Tan wire) and "B" (Purple/White or Purple wire). Monitor HO2S voltage on scan tool. If scan tool indicates a voltage of less than 200 millivolts, go to step 13. If scan tool does not indicate a voltage of less than 200 millivolts, go to step 9.
8. Turn ignition off. Repair cause of contamination. Replace HO2S. After replacing sensor, go to step 14.
9. Remove jumper wire from HO2S harness connector terminal "A". Using DVOM, check voltage between battery ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). If voltage is about 5 volts, go to step 12. If voltage is not about 5 volts, go to step 11.
10. Turn ignition off. Repair for a short to ground or a short to voltage in Purple/White or Purple wire between HO2S and PCM. After repairs, go to step 14.
11. Turn ignition off. Repair open in Tan/White or Tan wire between HO2S and PCM, or repair faulty PCM connections. After repairs, go to step 14.
12. Turn ignition off. Repair open in Purple/White or Purple wire between HO2S and PCM, or repair faulty PCM connections. After repairs, go to step 14.
13. Turn ignition off. Replace HO2S. After replacing sensor, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool observe the Stored information, Capture info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Note. Remove any debris from PCM connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure that gaskets are installed correctly to prevent water intrusion into PCM.

This diagnostic only runs once per ignition cycle. A malfunction in HO2S heater circuits causes a DTC to set. Check HO2S heater circuits for intermittent opens and for poor connections. The HO2S wires provide supply of oxygen. Check the HO2S wires and connections for breaks or for contamination.

Using the FREEZE FRAME/FAILURE RECORDS may help to locate an intermittent condition. If DTC cannot be duplicated, the information included in the FREEZE FRAME/FAILURE RECORDS can help determine how many miles since the DTC set. The fail and pass counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. In order to isolate when DTC failed, operate vehicle within the same FREEZE FRAME conditions. These conditions include, RPM, vehicle load and vehicle speed.

DTC P0134 OR P0154: HEATED OXYGEN SENSOR VOLTAGE STEADY WITHIN BIAS RANGE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC detects an HO2S that is lazy or slow when switching from lean-to-rich or from rich-to-lean. DTC is set when the average transition time is too long.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine run time is more than 409 seconds.
3. Ignition 1 signal is 9-18 volts.
4. Intrusive tests are not in progress.
5. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is steady between 350-550 millivolts for 60 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition off. Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to less than 350 or greater than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to less than 350 or greater than 550 millivolts, go to step 5.
3. Start and warm engine to normal operating temperature. Raise and hold engine speed at 1200 RPM for 2 minutes. Observe HO2S voltage on scan tool. If HO2S voltage is varying out of the 350-550 millivolts range, go to next step. If HO2S voltage is not varying out of the 350-550 millivolts range, go to step 5.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
5. Turn ignition off. Disconnect appropriate HO2S harness connector. Using a test light connected to battery voltage, probe HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 9.
6. Connect a jumper wire between HO2S harness connector terminals "A" (Tan/White or Tan wire) and "B" (Purple/White or Purple wire). Turn ignition on, with engine off. Observe HO2S voltage on scan tool. If HO2S voltage is less than 200 millivolts, go to step 10. If HO2S voltage is not less than 200 millivolts, go to next step.
7. Turn ignition off. Disconnect PCM harness connector C1. Check for open in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 22. If circuit is okay, go to next step.
8. Check for open in Tan/White or Tan wire between HO2S and PCM. Repair as necessary. After repairs, go to step 22. If circuit is okay, go to step 17.
9. Disconnect PCM harness connector C1. Check for open in Tan/White or Tan wire between HO2S and PCM. Repair as necessary. After repairs, go to step 22. If circuit is okay, go to step 17.
10. Turn ignition off. Remove jumper wire. Check ENG 1 fuse located in underhood fuse block. If fuse is open, go to step 13. If fuse is okay, go to next step.
11. Turn ignition on, with engine off. Using a test light connected to ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 18.
12. Connect test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 16. If test light does not illuminate, go to step 19.
13. Turn ignition off. Disconnect HO2S harness connector. Check Pink wire between HO2S harness connector and underhood fuse block for short to ground. Repair as necessary. After repairs, replace fuse, then go to step 22. If circuit is okay, go to next step.
14. Check Pink wire between HO2S harness connector and underhood fuse block for short to sensor body. Repair as necessary. After repairs, go to step 20. If circuit is okay, go to next step.
15. Check resistance between HO2S connector terminals "C" (Black wire) and "D" (Pink wire). If resistance is less than 2 ohms or greater than 50 ohms, go to step 20. If resistance is not less than 2 ohms or greater than 50 ohms, problem is intermittent.
16. Turn ignition off. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 22. If connections are okay, go to step 20.
17. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 22. If connections are okay, go to step 21.
18. Turn ignition off. Repair open in Pink wire. After repairs, go to step 22.
19. Turn ignition off. Repair open in Black wire. After repairs, go to step 22.
20. Replace HO2S. After replacing sensor, go to step 22.
21. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
22. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
23. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0134 OR P0154: HEATED OXYGEN SENSOR VOLTAGE STEADY WITHIN BIAS RANGE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

DTC monitors the HO2S voltage and detects if voltage goes out of the bias range (350-550 millivolts). If PCM does not detect that voltage went out of the bias range, a DTC sets.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine run time is more than 409 seconds.
3. Ignition 1 signal is 9-18 volts.
4. Intrusive tests are not in progress.
5. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is steady between 350-550 millivolts for 60 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to step 5.
3. Start and warm engine to normal operating temperature. Raise and hold engine speed at 1200 RPM for 2 minutes. Observe HO2S voltage on scan tool. If HO2S voltage is varying out of 350-550 millivolts range, go to next step. If HO2S voltage is not varying out of 350-550 millivolts range, go to step 5.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
5. Turn ignition off. Disconnect appropriate HO2S harness connector. Turn ignition on, with engine off. Connect 2 jumper wires to a known-good ground and connect jumpers to HO2S harness connector terminal "A" (Tan/White or Tan wire) and terminal "B" (Purple/White or Purple wire). (Scheme 6)or see scheme 7. Observe HO2S voltage on scan tool. If HO2S voltage is less than 200 millivolts, go to step 9. If HO2S voltage is not less than 200 millivolts, go to next step.
6. Remove both jumper wires from HO2S harness connector terminals. Check voltage between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). If voltage is greater than 4.5 volts, go to next step. If voltage is not greater than 4.5 volts, go to step 8.
7. Turn ignition off. Disconnect PCM harness connector C1. Check for open in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 21. If circuit is okay, go to step 16.
8. Turn ignition off. Disconnect PCM harness connector C1. Check for open in Tan/White or Tan wire between HO2S and PCM. Repair as necessary. After repairs, go to step 21. If circuit is okay, go to step 16.
9. Remove jumper wires. Check if OXYGEN fuse located in underhood fuse block is open. If fuse is open, go to step 12. If fuse is okay, go to next step.
10. Turn ignition on, with engine off. Using a test light connected to ground, probe HO2S harness connector terminal "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17.
11. Connect a test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 15. If test light does not illuminate, go to step 18.
12. Disconnect HO2S harness connector. Check for short to ground in Pink wire between HO2S and underhood fuse block. Repair as necessary. After repairs, replace fuse, then go to step 21. If circuit is okay, go to next step.
13. Check HO2S ignition voltage circuit for short to HO2S body. If circuit is shorted, go to step 19. If circuit is okay, go to next step.
14. Check resistance between HO2S terminals "C" and "D". If resistance is less than 2 ohms or greater than 50 ohms, go to step 19. If resistance is not less than 2 ohms or not greater than 50 ohms, problem is intermittent.
15. Turn ignition off. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 21. If connections are okay, go to step 19.
16. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 21. If connections are okay, go to step 19.
17. Turn ignition off. Repair open in Pink wire to fuse block. After repairs, go to step 21.
18. Turn ignition off. Repair open in Pink wire to fuse block. After repairs, go to step 21.
19. Replace HO2S. After replacing sensor, go to step 21.
20. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
21. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
22. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0135: HEATED OXYGEN SENSOR REMAINS WITHIN 150 MILLIVOLTS OF START-UP VOLTAGE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S heater circuit is functioning properly by monitoring the time required for HO2S to reach operating temperature. This DTC sets when PCM fails to detect HO2S voltage transitions greater than and less than the bias range within a specified amount of time.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1401 or P1441 is not set
2. HO2S voltage is 425-475 millivolts at engine start-up.
3. Intake air temperature and engine coolant temperature are less than 122°F (50°C), and are within 14.5°F (8°C) of each other at engine start-up.
4. Ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.
7. Scan tool is disconnected.

Conditions for setting DTC

1. The HO2S voltage remains within 150 millivolts of start-up voltage for a predetermined amount of time, based on ECT and airflow.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Allow engine to cool for one-half hour before proceeding with this test. This allows HO2S signal voltage to return to bias voltage (about 447 millivolts). Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to less than 350 millivolts or greater than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to less than 350 millivolts or greater than 550 millivolts, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Check ENG 1 fuse (located in underhood fuse block). If fuse is open, go to step 7. If fuse is okay, go to next step.
5. Disconnect appropriate HO2S harness connector. Turn ignition on, with engine off. Using a test light connected to known-good ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 11.
6. Connect test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 10. If test light does not illuminate, go to step 12.
7. Disconnect harness connectors from all HO2S. Check for short to ground in Pink wire between HO2S and fuse block. Repair as necessary. After repairs, replace fuse, then go to step 14. If circuits are okay, go to next step.
8. Turn ignition off. Check HO2S ignition 1 voltage circuit (Pink wire) on sensor side for short to HO2S body. If circuit is shorted, go to step 13. If circuit is okay, go to next step.
9. Check resistance between HO2S ignition 1 voltage circuit (Pink wire) and HO2S heater ground circuit (Black wire) on sensor side. Sensor resistance should be 2-50 ohms. If resistance is not as specified, go to step 13. If resistance is as specified, check for intermittent or poor connections in circuits.
10. Turn ignition off. Check for poor connections HO2S harness connector. Repair as necessary. After repairs, go to step 14. If connections are okay, go to step 13.
11. Turn ignition off. Repair open in Pink wire. After repairs, go to step 14.
12. Turn ignition off. Repair open in Black wire. After repairs, go to step 14.
13. Replace affected HO2S. After replacing sensor, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Disconnect scan tool. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Install scan tool. Check for DTCs. If DTC runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0135: HEATED OXYGEN SENSOR REMAINS WITHIN 150 MILLIVOLTS OF START-UP VOLTAGE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S heater circuit is functioning properly by monitoring the time required for HO2S to reach operating temperature. This DTC sets when PCM fails to detect HO2S voltage transitions at greater than and less than the bias range within a specified amount of time.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. HO2S voltage is 425-475 millivolts at engine start-up.
3. Intake air temperature and engine coolant temperature are less than 122°F (50°C) and within 14.5°F (8°C) of each other at engine start-up.
4. Ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.
7. Scan tool is disconnected.

Conditions for setting DTC

1. The HO2S voltage remains within 150 millivolts of start-up voltage for a predetermined amount of time, based on ECT and airflow.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Using scan tool, observe HO2S voltage for 2 minutes. If HO2S voltage goes from bias voltage to greater than 300 millivolts or less than 600 millivolts, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If HO2S voltage does not go from bias voltage to greater than 300 millivolts or less than 600 millivolts, go to next step.
3. Turn ignition off. Check OXYGEN fuse, located in underhood fuse block. If fuse is open, go to step 11. If fuse is okay, go to next step.
4. Disconnect HO2S harness connector. Using a test light connected to a known-good ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6)or see scheme 7. 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 terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 8.
6. Check resistance between HO2S Ignition 1 voltage (Brown wire) and HO2S heater ground (Brown wire) at HO2S pigtail. If resistance is 2-50 ohms, go to step 9. If resistance is not 2-50 ohms, go to step 10.
7. Repair open in circuit. After repairs, go to step 12.
8. Repair open in circuit. After repairs, go to step 12.
9. Check for poor connection at HO2S harness terminals. Repair as necessary. After repairs, go to step 12. If connection is okay, go to next step.
10. Replace HO2S. After replacing sensor, go to step 12.
11. Locate and repair short to ground in HO2S ignition 1 voltage circuit (Pink wire). Replace fuse. After repairs, go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Disconnect scan tool. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Install scan tool. Recheck DTCs. If DTC runs and passes, go to next step. If DTC resets, go to step 2.
13. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0137: HEATED OXYGEN SENSOR VOLTAGE REMAINS LOW ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains low for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1415, P1416, P1514, P1515, P1516, P1517 or P1518 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. The throttle position is 3-70 percent.
4. System operating in closed-loop.
5. Ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress.
8. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is less than 26 millivolts for 750 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Warm engine to normal operating temperature. Using scan tool, monitor HO2S voltage. If HO2S voltage is fixed at less than 26 millivolts, go to step 4. If HO2S voltage is not fixed at less than 26 millivolts, go to next step.
3. Turn ignition off. The condition that set this DTC is not present. This DTC may have been set by HO2S high signal wire intermittently shorted to an engine ground or to HO2S low reference circuit, water intrusion into HO2S connector, or exhaust leak between HO2S and engine. DTC can also be set by intermittent lean engine condition such as vacuum leak, incorrect or defective PCV, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect HO2S harness connector. Turn ignition on, with engine off. Using scan tool, monitor HO2S voltage. If HO2S voltage 351-551 millivolts, go to next step. If HO2S voltage is not 351-551 millivolts, go to step 6.
5. Check for water intrusion into HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, go to step 8.
6. Disconnect PCM harness connector C1. Using a DVOM, check resistance between ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). (Scheme 6) Check resistance between HO2S harness connector terminals "A" (Tan/White or Tan wire) and "B" (Purple/White or Purple wire). If resistance is infinite on both tests, go to step 9. If resistance is not infinite on both tests, go to next step.
7. Repair Purple/White or Purple wire for short to ground or short to Tan/White or Tan wire in HO2S circuit. After repairs, go to step 10.
8. Replace HO2S. After replacing sensor, go to step 10.
9. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
10. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check for a mispositioned sensor pigtail or sensor pigtail contacting exhaust system. Check for intermittent ground in wire between connector and sensor, poor PCM ground, lean injectors or contaminated fuel supply. Water causes a lean exhaust and can also set this DTC. Check fuel pressure. To confirm a low fuel pressure, monitor fuel pressure while driving vehicle at various speeds and loads. Check for exhaust leak, vacuum leak or crankcase leaks that can cause a lean condition or a high idle.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0137: HEATED OXYGEN SENSOR VOLTAGE REMAINS LOW ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains low for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1415, P1416, P1514, P1515, P1516, P1517 or P1518 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System is operating in closed-loop.
5. Ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress.
8. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is less than 26 millivolts for 750 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Allow engine to reach operating temperature. Using scan tool, observe HO2S voltage. If HO2S voltage is less than 26 millivolts, go to step 4. If HO2S voltage is not less than 25 millivolts, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect HO2S harness connector. Connect a jumper wire between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6)or see scheme 7. Turn ignition on, with engine off. Observe HO2S voltage on scan tool. If HO2S voltage is 350-550 millivolts, go to next step. If HO2S voltage is not 350-550 millivolts, go to step 6.
5. Turn ignition off. Check for water intrusion into HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 12. If no problem is found, go to step 8.
6. Turn ignition off. Disconnect PCM harness connector C1. Check for short to ground in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 12. If circuit is okay, go to next step.
7. Check Purple/White or Purple wire for short to Tan/White or Tan wire in HO2S circuit. Repair as necessary. After repairs, go to step 12. If circuits are okay, go to step 9.
8. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 12. If connections are okay, go to step 10.
9. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 12. If connections are okay, go to step 11.
10. Replace affected HO2S. After replacing sensor, go to step 12.
11. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
13. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Remove any debris from PCM connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure that the gaskets are installed correctly to prevent water intrusion into PCM.

Check HO2S pigtail may be in contact with exhaust manifold or exhaust system. Check HO2S oxygen supply. An oxygen supply inside HO2S is necessary for proper operation. HO2S wires provide supply of oxygen. Check HO2S wires and connections for breaks or contamination. Check for an intermittent ground in signal wire between connector and sensor.

Check lean injectors, fuel contamination, fuel pressure, exhaust leaks, vacuum leaks or for crankcase leaks that can cause a lean condition. If the components are okay, replace HO2S.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0138: HEATED OXYGEN SENSOR VOLTAGE REMAINS HIGH ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

DTC is designed to detect an HO2S voltage that remains high for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1414 or P1441 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System operating in closed-loop.
5. Ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress.
8. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is greater than 994 millivolts for 550 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Warm engine to normal operating temperature. Using scan tool, monitor HO2S voltage. If HO2S voltage is fixed at greater than 944 millivolts, go to step 4. If HO2S voltage is not fixed at greater than 944 millivolts, go to next step.
3. The condition that set this DTC is not present. This DTC may have been set by HO2S signal wire intermittently shorted to voltage, water intrusion into HO2S connector, silicone contaminated HO2S, intermittent rich engine condition, EVAP canister purge condition, engine oil contaminated by fuel, incorrect fuel pressure, leaking fuel pressure regulator, rich fuel injectors, or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect HO2S harness connector. Turn ignition on, with engine off. Using scan tool, monitor HO2S voltage. If HO2S voltage is 351-551 millivolts, go to next step. If HO2S voltage is not 351-551 millivolts, go to step 6.
5. Turn ignition off. Check for water intrusion into HO2S connector, silicone contaminated HO2S, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, leaking fuel pressure regulator, rich fuel injectors or inaccurate MAF sensor. Repair as necessary. After repairs, go to step 10. If no problem is found, go to step 8.
6. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on, with engine off. Using a DVOM, check voltage between ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). (Scheme 6) If voltage is greater than 20 millivolts, go to next step. If voltage is not greater than 20 millivolts, go to step 9.
7. Repair short to voltage in Purple/White or Purple wire between HO2S and PCM. After repairs, go to step 10.
8. Replace HO2S. After replacing sensor, go to step 10.
9. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
10. Turn ignition on, with engine off. Using scan tool, clear DTC. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Observe the DTC Status for this DTC. If this DTC runs and passes, go to next step. If DTC resets, go to step 2.
11. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Note. Never solder the HO2S wires.

Check fuel pressure. PCM can compensate for some increase. However, if pressure gets too high, DTC may set. Check for leaking injector, engine oil contaminated by fuel, EVAP canister purge for fuel saturation, leaking fuel pressure regulator diaphragm, intermittent TP sensor output or false rich HO2S indication due to contamination.

Check for intermittent conditions caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P0138: HEATED OXYGEN SENSOR VOLTAGE REMAINS HIGH ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

DTC is designed to detect an HO2S voltage that remains high for more than a specified number of seconds during the test conditions.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Air/fuel ratio is 14.5:1 and 14.7:1.
3. Throttle position is 3-70 percent.
4. System operating in closed-loop.
5. Ignition 1 signal is 9-18 volts.
6. Fuel tank level remaining is more than 10 percent.
7. Intrusive tests are not in progress.
8. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is greater than 994 millivolts for 550 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Allow engine to reach operating temperature. Using scan tool, observe HO2S voltage. If HO2S voltage is greater than 994 millivolts, go to step 4. If HO2S voltage is not greater than 994 millivolts, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect HO2S harness connector. Connect a jumper wire between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6)or see scheme 7. Turn ignition on, with engine off. Observe HO2S voltage on scan tool. If HO2S voltage is within 350-550 millivolts, go to next step. If HO2S voltage is not within 350-550 millivolts, go to step 6.
5. Turn ignition off. Check for water intrusion into HO2S connector, silicone contamination, engine oil contaminated by fuel, incorrect fuel pressure, rich fuel injectors, inaccurate MAF sensor, or EVAP canister purge condition. Repair as necessary. After repairs, go to step 11. If no problem is found, go to step 7.
6. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on with engine off. Check for short to voltage in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 11. If circuit is okay, go to step 8.
7. Check for poor connections at HO2S harness connector. Repair as necessary. After repairs, go to step 11. If connections are okay, go to step 9.
8. Turn ignition off. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 11. If connections are okay, go to step 10.
9. Replace affected HO2S. After replacing sensor, go to step 11.
10. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
11. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
12. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check HO2S connections for evidence of water intrusion. Water in the connector causes the battery voltage supply to heater to bleed over to the signal circuit. Check fuel pressure. PCM compensates for some increase, but if fuel pressure is too high, a DTC may set. Check for rich injectors, leaking injector, fuel pressure regulator, EVAP canister purge for fuel saturation, MAF sensor, check HO2S oxygen supply (HO2S wires provides supply of oxygen), intermittent TP sensor output.

Check for an intermittent condition caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P0140: HEATED OXYGEN SENSOR VOLTAGE IS WITHIN BIAS RANGE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC monitors the HO2S voltage and detects if voltage goes out of the bias range (400-475 millivolts). If PCM does not detect that voltage went out of the bias range, DTC will set.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine run time is more than 409 seconds.
3. System operating in closed-loop.
4. Ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is steady between 400-475 millivolts for 150 seconds.
2. Throttle position changes more than 5 percent within one second for 6 times.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to step 5.
3. Start engine and allow to reach operating temperature. Raise and hold engine speed at 1200 RPM for 2 minutes. Observe HO2S voltage on scan tool. If HO2S voltage is varying outside of 350-550 millivolts range, go to next step. If HO2S voltage is not varying outside of 350-550 millivolts range, go to step 5.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
5. Turn ignition off. Disconnect affected HO2S harness connector. Using a test light connected to battery voltage, probe HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 9.
6. Using a fused jumper wire, jumper HO2S harness connector terminals "A" (Tan/White or Tan wire) and "B" (Purple/White or Purple wire). Turn ignition on, with engine off. Observe HO2S voltage on scan tool. If HO2S voltage is less than 200 millivolts, go to step 10. If HO2S voltage is not less than 200 millivolts, go to next step.
7. Turn ignition off. Disconnect PCM harness connector C1. Check for open in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 22. If circuit is okay, go to next step.
8. Check for open in Tan/White or Tan wire between HO2S and PCM. Repair as necessary. After repairs, go to step 22. If circuit is okay, go to step 17.
9. Disconnect PCM harness connector C1. Check for open in Tan/White or Tan wire between HO2S and PCM. Repair as necessary. After repairs, go to step 22. If circuit is okay, go to step 17.
10. Turn ignition off. Remove jumper wire. Check ENG 1 fuse located in underhood fuse block. If fuse is open, go to step 13. If fuse is okay, go to next step.
11. Turn ignition on, with engine off. Using test light connected to ground, probe HO2S harness connector terminal "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 18.
12. Connect test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 16. If test light does not illuminate, go to step 19.
13. Disconnect harness connector from all HO2S. Check for short to ground in Pink wire to underhood fuse block. Repair as necessary. After repairs, replace fuse, then go to step 22. If circuit is okay, go to next step.
14. Check HO2S ignition 1 voltage circuit (Black wire) on sensor side for a short to HO2S body. If circuit is shorted, go to step 20. If circuit is okay, go to next step.
15. Check resistance between HO2S ignition 1 voltage circuit (Pink wire) and HO2S heater ground circuit (Black wire) on sensor side. If resistance is 2-50 ohms, go to step 20. If resistance is not greater than 2-50 ohms, check for intermittent or poor connections.
16. Turn ignition off. Check poor connections at affected HO2S harness connector. Repair as necessary. After repairs, go to step 22. If connections are okay, go to step 20.
17. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 22. If connections are okay, go to step 21.
18. Turn ignition off. Repair open in Pink wire to fuse block. After repairs, go to step 22.
19. Turn ignition off. Repair open in Black wire to ground connection. After repairs, go to step 22.
20. Replace affected HO2S. After replacing sensor, go to step 22.
21. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
22. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
23. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0140: HEATED OXYGEN SENSOR VOLTAGE IS WITHIN BIAS RANGE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC monitors HO2S voltage and detects if voltage goes out of the bias range (400-475 millivolts). If PCM does not detect that voltage went out of the bias range, a DTC sets.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine run time is more than 409 seconds.
3. System operating in closed-loop.
4. Ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.

Conditions for setting DTC

1. HO2S voltage is steady between 400-475 millivolts for 150 seconds.
2. Throttle position changes more than 5 percent within one second for 6 times.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to greater than 350 millivolts or to less than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to greater than 350 millivolts or to less than 550 millivolts, go to step 5.
3. Start and allow engine to reach operating temperature. Raise and hold engine speed at 1200 RPM for 2 minutes. Observe HO2S voltage on scan tool. If HO2S voltage is varying outside of 400-475 millivolts range, go to next step. If HO2S voltage is not varying outside of 400-475 millivolts range, go to step 5.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
5. Turn ignition off. Disconnect affected HO2S connector. Turn ignition on, with engine off. Connect a jumper wire between a known-good ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). (Scheme 6)or see scheme 7. Connect a jumper between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). Observe HO2S voltage on scan tool. If HO2S voltage is less than 200 millivolts, go to step 9. If HO2S voltage is not less than 200 millivolts, go to next step.
6. Remove both jumper wires. Check voltage between a known-good ground and HO2S harness connector terminal "A" (Tan/White or Tan wire). If voltage is greater than 4.5 volts, go to next step. If voltage is not greater than 4.5 volts, go to step 8.
7. Turn ignition off. Disconnect PCM harness connector C1. Check for open in Purple/White or Purple wire between HO2S and PCM. Repair as necessary. After repairs, go to step 21. If circuit is okay, go to step 16.
8. Turn ignition off. Disconnect PCM harness connector C1. Check for open in Tan/White or Tan wire between HO2S and PCM. Repair as necessary. After repairs, go to step 21. If circuit is okay, go to step 16.
9. Remove jumpers wire. Check OXYGEN fuse located in underhood fuse block. If fuse is open, go to step 12. If fuse is okay, go to next step.
10. Turn ignition on, with engine off. Using a test light connected to ground, probe HO2S harness connector terminal "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17.
11. Connect test light between HO2S harness connector terminals "(" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 15. If test light does not illuminate, go to step 18.
12. Disconnect harness connectors from all HO2S. Check for short to ground in Pink wire from HO2S to underhood fuse block. Repair as necessary. After repairs, replace fuse, then go to step 21. If circuit is okay, go to next step.
13. Check HO2S ignition 1 voltage circuit (Pink wire), sensor side, for short to HO2S body. If circuit is shorted, go to step 19. If circuit is okay, go to next step.
14. Check resistance between HO2S ignition 1 voltage circuit (Brown wire) and HO2S heater ground circuit (Brown wire) on sensor side. If resistance is 2-50 ohms, go to step 19. If resistance is not 2-50 ohms, problem is intermittent.
15. Turn ignition off. Check for poor connections at affected HO2S harness connector. Repair as necessary. After repairs, go to step 21. If connections are okay, go to step 19.
16. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 21. If connections are okay, go to step 20.
17. Turn ignition off. Repair open in Pink wire to fuse block. After repairs, go to step 21.
18. Turn ignition off. Repair open in Black wire to ground. After repairs, go to step 21.
19. Replace the affected HO2S. After replacing sensor, go to step 21.
20. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
21. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
22. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0141: HEATED OXYGEN SENSOR REMAINS WITHIN 150 MILLIVOLTS OF START-UP VOLTAGE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S heater circuit is functioning properly by monitoring amount of time required for HO2S to reach operating temperature. This DTC sets when PCM fails to detect HO2S voltage transitions at greater than or less than the bias range within a specified time.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. HO2S voltage is 425-475 millivolts at engine start-up.
3. Intake air temperature and engine coolant temperature are less than 122°F (50°C) and within 14.5°F (8°C) of each other at engine start-up.
4. Ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress
6. Scan tool output controls are not active.
7. Scan tool is disconnected.

Conditions for setting DTC

1. HO2S voltage remains within 150 millivolts of start-up voltage for a predetermined amount of time, based on ECT and airflow.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does reset, problem is intermittent.
4. Turn ignition off. Check ENG 1 fuse located in underhood fuse block. If fuse is open, go to step 7. If fuse is okay, go to next step.
5. Disconnect affected HO2S harness connector. Turn ignition on, with engine off. Using a test light connected to a known-good ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 11.
6. Connect test light between HO2S harness connector terminal "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 10. If test light does not illuminate, go to step 12.
7. Disconnect harness connectors from all HO2S. Check Pink wire for short to ground. Repair as necessary. After repairs, replace fuse, then go to step 14. If circuit is okay, go to next step.
8. Check the HO2S ignition 1 voltage circuit (Pink wire) for short to HO2S body on sensor side. If circuit is shorted, go to step 13. If circuit is okay, go to next step.
9. Check resistance between HO2S ignition 1 voltage circuit (Pink wire) and HO2S heater ground circuit (Black wire) on sensor side. If resistance is 2-50 ohms, go to step 13. If resistance is not greater than 2-50 ohms, problem is intermittent.
10. Turn ignition off. Check for poor connections at affected HO2S harness connector. Repair as necessary. After repairs, go to step 14. If connections are okay, go to step 13.
11. Turn ignition off. Repair open in Pink wire. After repairs, go to step 14.
12. Turn ignition off. Repair open in Black wire. After repairs, go to step 14.
13. Replace the affected HO2S. After replacing sensor, go to step 14.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Disconnect scan tool. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Install scan tool. Recheck for DTCs. If DTC runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0141: HEATED OXYGEN SENSOR REMAINS WITHIN 150 MILLIVOLTS OF START-UP VOLTAGE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S heater circuit is functioning properly by monitoring the amount of time required for HO2S to reach operating temperature. This DTC sets when PCM fails to detect HO2S voltage transitions greater than and less than the bias range within a specified time.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. HO2S voltage is 425-475 millivolts at engine start-up.
3. Intake air temperature and engine coolant temperature are less than 122°F (50°C) and within 14.5°F (8°C) of each other at engine start-up.
4. The ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.
7. Scan tool is disconnected.

Conditions for setting DTC

1. HO2S voltage remains within 150 millivolts of start-up voltage for a predetermined amount of time, based on ECT and airflow.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Using scan tool, observe HO2S voltage for 2 minutes. If HO2S voltage goes from a bias voltage to greater than 300 millivolts or less than 600 millivolts, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If HO2S voltage does not go from a bias voltage to greater than 300 millivolts or less than 600 millivolts, go to next step.
3. Check OXYGEN fuse located in underhood fuse block. If fuse is open, go to step 11. If fuse is okay, go to next step.
4. Disconnect HO2S harness connector. Using a test light connected to known-good ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6)or see scheme 7. 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 terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 8.
6. Turn ignition off. Check resistance between HO2S connector terminals "C" (Black wire) and "D" (Pink wire). If resistance is 2-50 ohms, go to step 9. If resistance is not 2-50 ohms, go to step 10.
7. Turn ignition off. Repair open in Pink wire to fuse block. After repairs, go to step 12.
8. Turn ignition off. Repair open in Black wire to ground circuit. After repairs, go to step 12.
9. Check for poor connection at HO2S harness terminals. Repair as necessary. After repairs, go to step 12. If connection is okay, go to next step.
10. Replace HO2S. After replacing sensor, go to step 12.
11. Turn ignition off. Locate and repair short to ground in Pink wire to fuse block. After repairs, replace fuse, then go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Disconnect scan tool. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Install scan tool. Recheck for DTCs. If DTC runs and passes, go to next step. If DTC resets, go to step 2.
13. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Use FREEZE FRAME/FAILURE RECORDS in order to help locate an intermittent condition. If DTC cannot be duplicated, information in the FREEZE FRAME/FAILURE RECORDS can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. In order to isolate when DTC failed, operate vehicle within the same FREEZE FRAME conditions such as RPM, load, vehicle speed, temperature, etc. observed. Check for intermittent conditions. Conditions might include RPM, vehicle load, vehicle speed and temperature. The heater diagnostic will only run on a cold start and run once per ignition cycle. An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Check HO2S wires for breaks or for contamination.

DTC P0155: HEATED OXYGEN SENSOR REMAINS WITHIN 150 MILLIVOLTS OF START-UP VOLTAGE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S heater circuit is functioning properly by monitoring the time required for HO2S to reach operating temperature. This DTC sets when PCM fails to detect HO2S voltage transitions greater than and less than the bias range within a specified time.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. HO2S voltage is 425-475 millivolts at engine start-up.
3. Intake air temperature and engine coolant temperature are less than 122°F (50°C) and within 14.5°F (8°C) of each other at engine start-up.
4. The ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.
7. Scan tool is disconnected.

Conditions for setting DTC

1. The HO2S voltage remains within 150 millivolts of start-up voltage for a predetermined amount of time, based on ECT and airflow.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Allow engine to cool for one-half hour before proceeding with this test. This allows HO2S signal voltage to return to bias voltage (about 447 millivolts). Turn ignition on, with engine off. Immediately observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to next step. If HO2S voltage does not go from bias voltage to greater than 350 millivolts or less than 550 millivolts, go to step 4.
3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
4. Turn ignition off. Check ENG 1 fuse located in underhood fuse block. If fuse is open, go to step 7. If fuse is okay, go to next step.
5. Disconnect HO2S harness connector. Turn ignition on, with engine off. Using a test light connected to a known-good ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 11.
6. Connect a test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to step 10. If test light does not illuminate, go to step 12.
7. Disconnect harness connector to all HO2S. Check for short to ground in Pink wire between HO2S and underhood fuse block. Repair as necessary. After repairs, replace fuse, then go to step 14. If circuit is okay, go to next step.
8. Check HO2S ignition 1 voltage circuit (Pink wire) on sensor side for short to HO2S body. If circuit is shorted, go to step 13. If circuit is okay, go to next step.
9. Check resistance between HO2S ignition 1 voltage circuit (Pink wire) and HO2S heater ground circuit (Black wire) on sensor side. If resistance is 2-50 ohms, go to step 13. If resistance is not 2-50 ohms, problem is intermittent.
10. Turn ignition off. Check for poor connections affected HO2S harness connector. Repair as necessary. After repairs, go to step 14. If connections are okay, go to step 13.
11. Turn ignition off. Repair open in Pink wire. After repairs, go to step 14.
12. Turn ignition off. Repair open in Black wire. After repairs, go to step 14.
13. Replace affected HO2S. After replacing sensor, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Disconnect scan tool. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Install scan tool. Recheck for DTCs. If DTC runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0155: HEATED OXYGEN SENSOR REMAINS WITHIN 150 MILLIVOLTS OF START-UP VOLTAGE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S heater circuit is functioning properly by monitoring the time required for HO2S to reach operating temperature. This DTC sets when PCM fails to detect HO2S voltage transitions greater than and less than the bias range within a specified time.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. HO2S voltage is 425-475 millivolts at engine start-up.
3. Intake air temperature and engine coolant temperature are less than 122°F (50°C) and within 14.5°F (8°C) of each other at engine start-up.
4. The ignition 1 signal is 9-18 volts.
5. Intrusive tests are not in progress.
6. Scan tool output controls are not active.
7. Scan tool is disconnected.

Conditions for setting DTC

1. The HO2S voltage remains within 150 millivolts of start-up voltage for a predetermined amount of time, based on ECT and airflow.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Using scan tool, observe HO2S voltage for 2 minutes on scan tool. If HO2S voltage goes from a bias voltage to greater than 300 millivolts or less than 600 millivolts, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If HO2S voltage does not go from a bias voltage to greater than 300 millivolts or less than 600 millivolts, go to next step.
3. Check OXYGEN fuse located in underhood fuse block. If fuse is open, go to step 11. If fuse is okay, go to next step.
4. Disconnect HO2S harness connector. Using a test light connected to a known-good ground, probe HO2S harness connector terminal "D" (Pink wire). (Scheme 6)or see scheme 7. 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 terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 8.
6. Turn ignition off. Check resistance between HO2S connector terminals "C" (Black wire) and "D" (Pink wire). If resistance is 2-50 ohms, go to step 9. If resistance is not 2-50 ohms, go to step 10.
7. Turn ignition off. Repair open in Pink wire. After repairs, go to step 12.
8. Turn ignition off. Repair open in Black wire. After repairs, go to step 12.
9. Check for a poor connection at HO2S harness terminals. Repair as necessary. After repairs, go to step 12. If connections are okay, go to next step.
10. Replace HO2S. After replacing sensor, go to step 12.
11. Turn ignition off. Locate and repair short to ground in Pink wire to underhood fuse block. Repair as necessary. After repairs, replace fuse, then go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Disconnect scan tool. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Install scan tool. Recheck DTCs. If DTC runs and passes, go to next step. If DTC resets, go to step 2.
13. Using scan tool observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Note. Remove any debris from PCM connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure that gaskets are installed correctly to prevent water intrusion into PCM.

This diagnostic only runs once per ignition cycle. A malfunction in HO2S heater circuits causes a DTC to set. Check HO2S heater circuits for intermittent opens and for poor connections. The HO2S wires provide supply of oxygen. Check the HO2S wires and connections for breaks or for contamination.

Using the FREEZE FRAME/FAILURE RECORDS may help to locate an intermittent condition. If DTC cannot be duplicated, the information included in the FREEZE FRAME/FAILURE RECORDS can help determine how many miles since the DTC set. The fail and pass counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. In order to isolate when DTC failed, operate vehicle within the same FREEZE FRAME conditions. These conditions include, RPM, vehicle load and vehicle speed.

DTC P0171 OR P0174: FUEL TRIM SYSTEM LEAN

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open and closed-loop. During open-loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed-loop, oxygen sensor inputs are added and used by PCM to calculate short and long term fuel trim, fuel delivery adjustments. If oxygen sensors indicate a lean condition, fuel trim values will be greater than zero percent. If oxygen sensors indicate a rich condition, fuel trim values will be less than zero percent. Short term fuel trim values change rapidly in response to HO2S voltage signals. Long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. If PCM detects an excessively lean condition, this DTC will set.

Conditions for running DTC

1. DTCs P0101, P0103, P0108, P0135, P0137, P0141, P0200, P0300, P0410, P0420, P0430, P0440, P0442, P0443, P0446, P0449, P0506, P0507 or P1441 is not set
2. Engine coolant temperature is 167-239°F (75-115°C).
3. Intake air temperature is 4-194°F (-20 to 90°C).
4. Manifold absolute pressure is 3.7-13 psi (26-90 kPa).
5. Vehicle speed is less than 85 MPH.
6. Engine speed is 400-3000 RPM.
7. Barometric pressure is greater than 10.7 psi (74 kPa).
8. Mass airflow is 5-90 grams/second.
9. Fuel level is more than 10 percent.
10. Throttle position is less than 90 percent.

Conditions for setting DTC

1. Average long term fuel trim cell value is greater than 23 percent for 6 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start and warm engine to normal operating temperature. Ensure engine is operating in closed-loop. Record the long term fuel trim. Turn ignition off. Turn ignition on, with engine off. Review the FREEZE FRAME/FAILURE RECORDS and record displayed data for this DTC. If scan tool indicates that the long term fuel trim value is greater than 23 percent, go to next step. If scan tool does not indicate that the long term fuel trim value is greater than 23 percent, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
3. Start and operate engine at idle. Using scan tool, observe HO2S parameters. If scan tool indicates that parameter is within the 200-800 millivolts range and fluctuating, go to next step. If scan tool does not indicate that parameter is within the 200-800 millivolts range and fluctuating, go to step 5 .
4. Turn ignition off. Visually and physically inspect vacuum hoses for splits, kinks, and proper connections. Ensure that vehicle has sufficient fuel in tank. If fuel pressure is too low this DTC may set. Repair as necessary. After repairs, go to step 7 . If no problem is found, go to step 6 .
5. Turn ignition off. Check HO2S for proper installation. Ensure connectors and wires are secured and not contacting exhaust system. Repair as necessary. After repairs, go to step 7 . If no problem is found, diagnose fuel system.
6. Operate engine at idle. Check for missing, loose, or leaking exhaust components forward of HO2S. Check for vacuum leaks at intake manifold, throttle body, and injector O-rings. Check air induction system and air intake ducts for leaks. Check the secondary air injection (AIR) system for leaks, improper air delivery, shut off valve not closing. Check crankcase ventilation system for leaks. Repair as necessary. After repairs, go to next step. If no problem is found, check for engine mechanical problem.
7. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
8. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

The system will go lean if an injector is not suppling enough fuel. A lean condition could be present during high fuel demand. Using scan tool, review FAILURE RECORDS. Diagnose intermittent condition.

DTC P0172 OR P0175: FUEL TRIM SYSTEM RICH

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open and closed-loop. During open loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed-loop, oxygen sensor inputs are added and used by PCM to calculate short and long term fuel trim, fuel delivery adjustments.

If oxygen sensors indicate a lean condition, fuel trim values will be greater than zero percent. If oxygen sensors indicate a rich condition, fuel trim values will be less than zero percent. Short term fuel trim values change rapidly in response to HO2S voltage signals. Long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the EVAP canister is causing a rich condition. If PCM detects an excessively rich condition, this DTC will set. If PCM detects excessive vapor, then a pass is logged.

Conditions for running DTC

1. DTCs P0101, P0103, P0108, P0135, P0137, P0141, P0200, P0300, P0410, P0420, P0430, P0440, P0442, P0443, P0446, P0449, P0506, P0507 or P1441 is not set
2. Engine coolant temperature is 167-239°F (75-115°C).
3. Intake air temperature is 4-194°F (-20 to 90°C).
4. Manifold absolute pressure is 3.7-13 psi (26-90 kPa).
5. Vehicle speed is less than 85 MPH.
6. Engine speed is 400-3000 RPM.
7. Barometric pressure is greater than 10.7 psi (74 kPa).
8. Mass airflow is 5-90 grams/second.
9. Fuel level is more than 10 percent.
10. Throttle position is less than 90 percent

Conditions for setting DTC

1. The average long term fuel trim value is less than -13 percent for 40 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start and warm engine normal operating temperature. Ensure engine is operating in closed-loop. Record the long term fuel trim data. Turn ignition off. Turn ignition on, with engine off. Review the FREEZE FRAME/FAILURE RECORDS and record displayed data for this DTC. If scan tool indicates that the long term fuel trim is less than -13 percent, go to next step. If scan tool does not indicate that the long term fuel trim is less than -13 percent, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
3. Operate engine at idle. Using scan tool, observe HO2S parameters. If scan tool indicates that values are within 200-800 millivolts range and fluctuating, go to next step. If scan tool does not indicates that values are within 200-800 millivolts range and fluctuating, go to step 5 .
4. Turn ignition off. Visually and physically inspect inlet screen of MAF sensor for blockage. Check vacuum hoses for splits, kinks and proper connections. Check for collapsed or restricted air intake duct, dirty or restricted air filter, or objects blocking throttle body. Repair as necessary. After repairs, go to step 7 . If no problem is found, go to step 6 .
5. Turn engine off. Check HO2S for proper installation. Ensure electrical connectors and wires are secured and not contacting exhaust system. Repair as necessary. After repairs, go to step 7 . If no problem is found, diagnose fuel system.
6. Check for excessive fuel in crankcase. Check evaporative emissions control system. Check fuel pressure regulator for proper operation. Ensure all injectors are functioning properly. Repair as necessary. After repairs, go to next step. If no problem is found, check for engine mechanical problem.
7. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
8. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check for fuel contamination, such as water and alcohol will effect fuel trim. A malfunctioning MAF sensor can cause a rich condition and set this DTC. Using scan tool, review FAILURE RECORDS data. If an intermittent condition is suspected, diagnose intermittent conditions.

DTC P0200: INCORRECT VOLTAGE FOR THE COMMANDED STATE OF INJECTOR DRIVER

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM enables the appropriate fuel injector on intake stroke for each cylinder. Ignition voltage is supplied to fuel injectors. PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. PCM monitors the status of each driver. If PCM detects an incorrect voltage for the commanded state of the driver, a fuel injector control DTC will set.

Conditions for running DTC

1. Engine is running.
2. Ignition voltage is 6-18 volts.

Conditions for setting DTC

1. PCM detects an incorrect voltage on fuel injector control circuit for 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, clear DTCs. Operate engine at idle and at normal operating temperature. Monitor the Misfire Current counters on scan tool. If any of the counters are incrementing, go to step 4 . If counters are not incrementing, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Turn ignition off. Disconnect fuel injector harness connector. Turn ignition on, with engine off. Using a test light connected to a known-good ground, probe the ignition 1 voltage supply circuit (Pink wire) of appropriate fuel injector. If test light illuminates, go to next step. If test light does not illuminate, go to step 11 .
5. Connect Fuel Injector Check Light (J-34730-375) between appropriate fuel injector harness connector. Crank engine. If injector test light flashes, go to step 9 . If injector test light does not flash, go to next step.
6. If injector test light remains illuminated at all times, go to step 8 . If injector test light does not remain illuminated at all times, go to next step.
7. Turn ignition off. Check affected fuel injector control circuit for open or short to voltage. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 10 .
8. Turn ignition off. Check affected fuel injector control circuit for short to ground. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 13 .
9. Turn ignition off. Check for poor connections fuel injector harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 12 .
10. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 13 .
11. Turn ignition off. Repair open or short to ground in ignition voltage supply circuit to affected fuel injector. After repairs, go to step 14 .
12. Replace fuel injector. After replacing injector, go to step 14 .
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
15. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Perform fuel injector coil test to help isolate an intermittent condition. See FUEL SYSTEMS (GASOLINE) in appropriate SYSTEM & COMPONENT TESTING article.

DTC P0230: INCORRECT VOLTAGE ON FUEL PUMP RELAY CONTROL CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS article.

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

Conditions for running DTC

1. Engine speed is greater than 400 RPM.
2. Ignition voltage is 6-18 volts.

Conditions for setting DTC

1. PCM detects that commanded state of injector driver and actual state of control circuit does not match for a minimum of 2.5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, command fuel pump on and off. If fuel pump relay turns on and off with each command, go to next step. If fuel pump relay does not turn on and off, go to step 4 .
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
4. Turn ignition off. Disconnect fuel pump relay (located in underhood fuse/relay block). Turn ignition on, with engine off. Using a test light connected to ground, probe fuel pump relay control circuit (Dark Green/White wire). Using scan tool, command fuel pump on and off. If test light turns on and off with each command, go to next step. If test light does not turn on or off, go to step 6 .
5. Connect test light between fuel pump relay control circuit (Dark Green/White wire) and ground circuit (Black wire). Using scan tool, command fuel pump on and off. If test light turns on and off with each command, go to step 9 . If test light does not turn on and off with each command, go to step 11 .
6. If test light remains on with each command, go to step 8 . If test light does not remain on with each command, go to next step.
7. Turn ignition off. Check fuel pump relay control circuit for short to ground or open circuit. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 10 .
8. Turn ignition off. Check fuel pump relay control circuit for short to voltage. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 10 .
9. Turn ignition off. Check for poor connections at fuel pump relay. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 12 .
10. Check for poor connections at PCM harness connectors. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 13 .
11. Turn ignition off. Repair fuel pump relay ground circuit. After repairs, go to step 14 .
12. Replace fuel pump relay. After replacing relay, go to step 14 .
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
15. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0300: ENGINE MISFIRE DETECTED

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM uses information from Crankshaft Position (CKP) sensors and Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, PCM is able to detect individual misfire events. A misfire rate that is high enough can cause three-way catalytic converter damage. The MIL will flash on and off when the conditions for catalytic converter damage are present.

Note. If start-up ECT is less than 20°F (7°C), misfire detection is delayed until ECT is greater than 70°F (21°C). If start-up ECT is greater than 20°F (7°C), misfire detection begins after a 5 second delay.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0117, P0118, P0128, P0335, P0336, P0341, P0343, P0500, P0502, P0503, P1114, P1115, P1121, P1122, P1220, P1258, P1336 or P1345 is not set
2. Fuel level is more than 10 percent
3. Engine speed is 450-5000 RPM.
4. System voltage is 11-16 volts.
5. Throttle position is steady within 2 percent for 100 milliseconds.

Conditions for setting DTC

1. PCM detects a deceleration in crankshaft speed that is characteristic of either an emission type misfire or of a catalyst-damaging type misfire.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, check if any other DTCs are set. Diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no other DTCs are set, go to next step.
3. Start engine. Using scan tool, clear DTCs. Allow engine to reach operating temperature. Observe the Misfire Current Counters on scan tool. If any of the Misfire Current Counters are incrementing, go to step 5 . If no Misfire Current Counters are incrementing, go to next step.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or operate vehicle within the conditions observed from the FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. If engine is misfiring, go to next step. If engine is not misfiring, diagnose for engine mechanical problem.
6. If only one Misfire Current Counter is incrementing, go to next step. If more than one Misfire Current Counter is incrementing, go to step 13 .
7. Turn ignition off. Disconnect spark plug wire from spark plug. Connect Spark Checker (J 26792) to spark plug wire and a good ground. Start and operate engine at idle. If spark tester sparks and spark is consistent, go to step 9 . If spark test does not spark or spark is inconsistent, go to next step.
8. Remove spark plug wire from cylinder that indicates a misfire. Check resistance of spark plug wire. If resistance is less than 625 ohms/foot, go to step 16 . If resistance is not less than 625 ohms/foot, go to step 15 .
9. Remove spark plug from cylinder that indicates a misfire. If spark plug is gas, coolant or oil fouled, determine cause of fouling. Repair as necessary. After repairs, go to step 17 . If no fouling is found, go to next step.
10. Swap suspected spark plug with another cylinder that is operating correctly. Start and operate engine within the conditions that misfire occurred. Using scan tool, monitor the Misfire Current Counters. If misfire moves with the spark plug, go to step 14 . If misfire did not move with spark plug, go to next step.
11. After performing fuel injector coil check, repair or replace as necessary. After repairs, go to step 17 . If no problem is found, go to next step.
12. Check vacuum hoses for splits, kinks and correct connections. Check for vacuum leaks at throttle body and at intake manifold. Check for clean, tight and in correct location. Check for contaminated fuel, correct fuel pressure, poor connections at ignition coil, faulty spark plug wires or coil wire. Check for fouled or damaged spark plugs. Check exhaust system for restrictions. Repair as necessary. After repairs, go to step 17 . If no problem is found, check for engine mechanical problem.
13. Turn ignition off. Check vacuum hoses for splits, kinks or proper connections. Check for vacuum leaks at throttle body and intake manifold. Check PCM grounds. Check for contaminated fuel or for correct fuel pressure. Check for poor connections at ignition coil, faulty spark plug wires or coil wire. Check for fouled or damaged spark plugs. Check distributor cap and distributor for damage. Check ignition coil for correct output. Check exhaust system for restrictions. Repair as necessary. After repairs, go to step 17 . If no problem is found, check for engine mechanical problem.
14. Replace spark plugs. After replacing spark plugs, go to step 17 .
15. Replace spark plug wires. After replacing spark plug wire, go to step 17 .
16. Replace distributor cap. After replacing distributor cap, go to step 17 .
17. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
18. Using scan tool, select Capture Info in order to observe the stored information. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Using scan tool, select Capture Info in order to observe the stored information. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay.

Many different conditions could cause an intermittent misfire. Check Ignition Control (IC) circuit for an intermittent short to ground. Ensure that spark plug wires are securely attached to spark plugs and distributor cap. Ensure that coil wire is securely attached to distributor cap and coil. Check wire routing to ensure that crossfiring is not occurring. If misfire occurs when weather is damp, the problem could be due to worn spark plug wires. Check fuel for contamination. Ensure fuel level is not too low. If fuel level is low, fuel pump may draw air into fuel rail, causing a stumble and a possible misfire condition. Check fuel trim number in the FREEZE FRAME in order to determine if this has occurred. This condition would be likely if short term fuel number is more than +20. Check for restricted fuel filter or sticking intake or exhaust valves on engines which misfire when engine is cold. Check HO2S for abnormal voltage readings. Check for vacuum leak as a possible cause of engine misfire.

DTC P0325: KNOCK SENSOR MODULE CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS article.

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

Conditions for running DTC

1. Engine run time is greater than 10 seconds.

Conditions for setting DTC

1. PCM detects a malfunction in KS diagnostic circuitry that will not allow proper diagnosis of KS system.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
3. Turn ignition off. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
4. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
5. Using a scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0327: KNOCK SENSOR CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS article.

The Knock Sensor (KS) produces an AC voltage at all engine speeds and loads. PCM adjusts the spark timing based on the amplitude and frequency of KS signal. The PCM uses the KS signal in order to calculate the average voltage, then PCM assigns a voltage value. The PCM checks the knock sensor and the related wiring by comparing actual knock signal to the assigned voltage range. A normal KS signal should stay within the assigned voltage range. This DTC will set if KS signal is outside the assigned voltage range or if signal is not present.

Conditions for running DTC

1. DTCs P0117, P0118, P0121, P0122, P0123, P0125, P1114, P1115, P1121 or P1122 is not set
2. Engine coolant temperature is greater than 140°F (60°C).
3. Engine run time is more than 10 seconds.
4. Manifold absolute pressure is less than 44 kPa.
5. Engine speed is 2000-3000 RPM.
6. System voltage is greater than 10 volts.

Conditions for setting DTC

1. Knock signal is out of assigned range or not present.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to the FREEZE FRAME/FAILURE RECORDS conditions. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
3. Using scan tool, save the FREEZE FRAME/FAILURE RECORDS data stored when DTC set. Turn ignition off and wait 30 seconds. Disconnect PCM harness connector. Using a DVOM set to 400 millivolts AC hertz scale, observe frequency between the KS signal circuit (Dark blue wire) and low reference circuit (Gray wire) while tapping on engine block with a non-metallic object. If frequency is fluctuating, go to step 6 . If frequency is not fluctuating, go to next step.
4. Turn ignition off. Disconnect KS harness connector. Check for open in KS signal circuit (Dark Blue wire) and low reference circuit (Gray wire). Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
5. Check for poor connections at KS harness connector. Repair as necessary. After repairs, go to step 11 . If connections are okay, go to step 9 .
6. Turn ignition off. Check for short to ground or for short to voltage in KS signal circuit (Dark Blue wire). Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
7. Check for short to ground or short to voltage in KS low reference circuit (Gray wire). Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
8. Check for poor connection at PCM harness connector. Repair as necessary. After repairs, go to step 11 . If connections are okay, go to step 10 .
9. Replace knock sensor. After replacing sensor, go to step 11 .
10. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
11. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC test runs and passes, go to next step. If DTC resets, go to step 2 .
12. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0335: CRANKSHAFT POSITION SENSOR SIGNAL NOT DETECTED

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 7

Crankshaft Position (CKP) sensor signal indicates the crankshaft speed and position. The CKP sensor is connected directly to PCM and consists of the 12-volt reference circuit, low reference circuit and signal circuit.

Conditions for running DTC

1. DTCs P0101, P0102, P0103 or P0341 is not set.
2. Camshaft position sensor is transitioning.
3. Mass airflow is greater than 3 grams/second in CRANK mode.
4. Mass airflow is greater than 5 grams/second in RUN mode.

Conditions for setting DTC

1. The crankshaft position sensor signal is not detected for more than 3 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine. If engine starts and continue to run, problem is intermittent. If engine does not start or starts but does not continue to run, go to next step.
3. Turn ignition off. Disconnect Crankshaft Position (CKP) sensor harness connector (located near crankshaft pulley). Turn ignition on, with engine off. Using a test light connected to ground, probe CKP sensor harness connector terminal "A" (Light Green wire). (Scheme 7) If test light illuminates, go to next step. If test light does not illuminate, go to step 6.
4. Connect test light between CKP sensor harness connector terminals "A" (Light Green wire) and "B" (Purple wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 7.
5. Turn ignition off. Using Connector Check Kit (J 35616-A), install Gray jumper wires from kit between CKP sensor harness connector terminals "A" (Light Green wire) and "B" (Gray wire). Using a DVOM set to duty cycle position, connect DVOM between CKP sensor harness connector terminals "B" (Gray wire) and "C" (Yellow wire). Select AC voltage and press Hz button twice in order to display duty cycle. Crank engine. If duty cycle is 40-60 percent, go to step 8. If duty cycle is not 40-60 percent, go to step 9.
6. Turn ignition off. Repair open or high resistance in Light Green wire. After repairs, go to step 15.
7. Turn ignition off. Check for open or high resistance in Purple wire. After repairs, go to step 15. If circuit is okay, go to step 13.
8. Check for open, high resistance, or short in Yellow wire. After repairs, go to step 15. If circuit is okay, go to step 11.
9. Check CKP sensor and crankshaft reluctor wheel for damage. Repair as necessary. After repairs, go to next step. If no problem is found, go to step 12.
10. Replace CKP sensor or crankshaft reluctor wheel. After repairs, go to step 15.
11. Check for faulty connections at CKP sensor. Repair as necessary. After repairs, go to step 15. If connections are okay, go to step 13.
12. Replace CKP sensor. After replacing sensor, go to step 15.
13. Check for faulty connections at PCM. Repair as necessary. After repairs, go to step 15. If connections are okay, go to next step.
14. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
15. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
16. Using scan tool, observe the stored information and Capture info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0336: CRANKSHAFT POSITION SENSOR SIGNAL OUT-OF-RANGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Crankshaft Position (CKP) sensor sends reference signal to PCM to indicate position of crankshaft and engine speed (RPM). PCM uses this information to determine ignition coil, fuel injector and ignition timing.

Conditions for running DTC

1. Engine is cranking or running.

Conditions for setting DTC

1. PCM determines that the CKP sensor signal is out-of-range for less than 3 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine and operate at idle for 2 minutes. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
3. Visually and physically inspect all circuits going to CKP sensor for being routed too close to secondary ignition wires or components, routed too close to aftermarket add-on electrical equipment, solenoids, relays and motors. Correct harness routing. After repairs, go to step 9 . If no problem is found, go to next step.
4. Check for poor connections at CKP sensor. Repair as necessary. After repairs, go to step 9 . If connections are okay, go to next step.
5. Check for poor connections at PCM sensor. Repair as necessary. After repairs, go to step 9 . If connections are okay, go to next step.
6. Remove CKP sensor. Check CKP sensor for signs of damage. Repair as necessary. After repairs, go to step 9 . If no problem is found, go to next step.
7. Check CKP reluctor wheel for damage. Repair as necessary. After repairs, go to step 9 . If no problem is found, go to next step.
8. Replace CKP sensor. After replacing sensor, go to next step.
9. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
10. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

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

Check crankshaft reluctor wheel for damage or improper installation. Check sensor coming in contact with reluctor wheel. Check for excessive crankshaft end play, causing CKP sensor reluctor wheel to move out of alignment with CKP sensor, resulting in a no-start, start and stall, or erratic performance. An improperly installed crankshaft could cause excessive crankshaft end play.

DTC P0341: CAMSHAFT POSITION SENSOR SIGNAL NOT DETECTED WHILE ENGINE IS RUNNING

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 8

The Camshaft Position (CMP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies CMP sensor with signal and ground circuits. Ignition voltage is supplied to CMP sensor by an independent circuit. CMP sensor produces a magnetic field whenever ignition is on. The CMP sensor is mounted near a reluctor wheel that is attached to distributor shaft. When distributor shaft rotates, or when engine is cranking or running, reluctor wheel changes the magnetic field. The CMP sensor converts each change in magnetic field into a pulse. The number of teeth on reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation. Control module uses CMP sensor signal in order to calculate correct timing for sequential fuel injection.

DTC will set when engine is running and CMP sensor reference pulse is not detected once every 2 crankshaft revolutions.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, monitor the CAM signal input high-to-low and low-to-high transition parameter. If parameter increments, go to next step. If parameter does not increment, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect CMP sensor harness connector. Turn ignition on, with engine off. Connect a DVOM between a known-good ground and CMP sensor harness connector terminal "C" (Red wire). (Scheme 8) If voltage reading is about battery voltage, go to step 6. If voltage reading is not about battery voltage, go to next step.
5. Turn ignition off. Disconnect PCM harness connector C2. Check for open in Red wire between CMP sensor and PCM harness connector C2 terminal No. 39. (Scheme 2) Repair as necessary. After repairs, go to step 16. If circuit is okay, go to step 12.
6. Connect a test light to battery voltage. Touch test light to CMP sensor harness connector terminal "A" (Pink/Black wire). (Scheme 8) If test light illuminates, go to step 8. If test light does not illuminate, go to next step.
7. Turn ignition off. Disconnect PCM harness connector C2. Check for open or high resistance in Pink/Black wire between CMP sensor and PCM harness connector C2 terminal No. 61. (Scheme 2) Repair as necessary. After repairs, go to step 16. If circuit is okay, go to step 12.
8. Start engine. Using scan tool, monitor the CMP signal high-to-low and low-to-high parameter. Connect a fused jumper wire to battery voltage and momentarily touch CMP sensor harness connectors terminal "B" (Brown/White wire) 5 times for a duration of one second each. If parameter changes each time signal circuit is touched, go to step 14. If parameter does not change each time signal circuit is touched, go to next step.
9. Turn ignition off. Check fuse in jumper wire. If fuse is open, go to step 11. If fuse is okay, go to next step.
10. Check for short to voltage, open or high resistance in Brown/White wire between CMP sensor and PCM harness connector C2 terminal No. 73. (Scheme 2) Repair as necessary. After repairs, go to step 16. If circuit is okay, go to step 12.
11. Check for short to ground in Brown/White wire between CMP sensor and PCM harness connector C2 terminal No. 73. (Scheme 2) Repair as necessary. After repairs, go to step 16. If circuit is okay, go to next step.
12. Check for poor connections at PCM. Repair as necessary. After repairs, go to step 16. If connections are okay, go to next step.
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to step 16.
14. Turn ignition off. Check for poor connections at CMP sensor. Repair as necessary. After repairs, go to step 16. If connections are okay, go to next step.
15. Replace CMP sensor. After replacing sensor, go to next step.
16. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
17. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

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

Electromagnetic Interference (EMI) from ignition coil or from spark plug wires could cause a faulty signal condition in CMP signal circuit to PCM. Ensure that routing of CMP circuitry is correct.

DTC P0351: IGNITION CONTROL VOLTAGE NOT WITHIN SPECIFIED RANGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Scheme 9

The enhanced ignition system uses the Crankshaft Position (CKP) sensor in order to provide a timing input to control module. Ignition Control (IC) spark timing for each cylinder is based on this input. The control module provides ignition timing signal to Ignition Control Module (ICM) to control the ignition coil. Each timing pulse detected by ICM allows PCM to energize ignition coil. A large secondary ignition voltage is induced in the secondary coil by the primary coil. This high voltage is switched to the correct spark plug by the distributor. This DTC will set if PCM detects an unusually high or low voltage on the ignition timing signal circuit.

Conditions for running DTC

1. Ignition control is enabled.
2. Engine speed is less than 250 RPM.

Conditions for setting DTC

1. Ignition control voltage is not within 0.04-4.9 volts.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, clear DTCs. Disconnect injector harness connector. Crank engine for 15 seconds. If DTC P0351 resets, go to next step. If DTC P0351 does not reset, problem is intermittent.
3. Turn ignition off. Reconnect injector harness connector. Disconnect ICM harness connector. Using a DVOM in AC scale, probe ICM harness connector terminal "B" (White wire). (Scheme 9) Crank engine. Observe DVOM voltage. If voltage reading is 1-4 volts, go to next step. If voltage reading is not 1-4 volts, go to step 6.
4. Turn ignition off. Using a test light connected to battery voltage, probe ICM harness connector terminal "C" (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 10.
5. Turn ignition on, with engine off. Using test light connected to ground, probe ICM harness connector terminal "A" (Pink wire). If test light illuminates, go to step 14. If test light does not illuminate, go to step 13.
6. Turn ignition off. Disconnect PCM harness connector. Using test light connected to battery voltage, probe PCM harness connector C2 terminal No. 26 (White wire). (Scheme 2) If test light illuminates, go to step 11. If test light does not illuminate, go to next step.
7. Check for open in White wire PCM and ICM harness connector. Repair as necessary. After repairs, go to step 16. If circuit is okay, go to next step.
8. Reconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM connected to ground and in DC scale, probe ICM harness connector terminal "B" (White wire). If voltage reading is greater than one volt, go to step 12. If voltage reading is not greater than one volt, go to next step.
9. Turn ignition off. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 16. If connections are okay, go to step 15.
10. Repair open in IC ground circuit (Black wire on "L" and "M" Series or Black/White wire on "S" and "T" Series). After repairs, go to step 16.
11. Repair short to ground in White wire between ICM and PCM. After repairs, go to step 16.
12. Turn ignition off. Repair short to voltage in White wire between ICM and PCM. After repairs, go to step 16.
13. Repair open in Pink wire between ICM and underhood fuse block. After repairs, go to step 16.
14. Turn ignition off. Replace ICM. After replacing module, go to step 16.
15. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
16. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
17. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0401: EGR SYSTEM - INSUFFICIENT FLOW

Note. For circuit reference, see WIRING DIAGRAMS article.

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 for running DTC

1. DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0404, P0405, P0502, P0503, P0506, P0507, P1111, P1112, P1114, P1115, P1121, P1122, P1404, P1635 or P1639 is not set
2. Ignition voltage is 11.7-18 volts.
3. Barometric pressure is greater than 70 kPa.
4. Engine coolant temperature is 140-243°F (60-117°C).
5. Intake air temperature is less than 140°F (65°C).
6. Engine speed is 725-2000 RPM.
7. Throttle position sensor angle is less than one percent.
8. Altitude compensated MAP is 3-6 psi (10-60 kPa).
9. Engine vacuum is 9-12 psi (60-83 kPa).
10. Idle air control position is steady.
11. Vehicle speed is 26-70 MPH.
12. Change in vehicle speed sensor is less than 4 MPH.
13. Change in manifold absolute pressure is less than 0.8 kPa.
14. A/C clutch status is steady.
15. Fuel system is not in deceleration fuel cut-off.

Conditions for setting DTC

1. Change in MAP is less than a predetermined value during EGR flow test.
2. Conditions are present for 2 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Check if any MAP sensor related DTCs are set. Diagnose affected DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no MAP sensor related DTCs are set, go to next step.
3. Turn ignition off. Check exhaust system for modification of original installed parts or leaks. Repair exhaust system as necessary. After repairs, go to step 7 . If no problem is found, go to next step.
4. Check EGR valve gasket and pipes for leaks. Clean or replace EGR system components as necessary. Repair as necessary. After repairs, go to step 7 . If no problem is found, go to next step.
5. Remove EGR valve. Visually and physically inspect for a leak or restriction, EGR pintle, and EGR valve passages. Repair as necessary. After repairs, go to step 7 . If no problem is found, go to next step.
6. Remove EGR inlet pipe from exhaust manifold. Check EGR ports and EGR inlet pipe for blockage caused by excessive deposits or other damage. Repair as necessary. After repairs, go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
7. Turn ignition on, with engine off. Using scan tool, select DTC option and clear DTC. Operate engine at idle and warm engine to normal operating temperature. Using scan tool, select DTC option and Specific DTC option, then enter DTC using scan tool. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
8. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check for faulty connections or damaged harness. Check PCM harness connector for backed-out terminal to EGR control circuit. 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. Ensure fuel injectors are functioning properly and check engine oil for fuel contamination.

Check for vacuum restriction to MAP sensor. A restriction to MAP sensor can cause EGR flow test to fail due to insufficient MAP changes being monitored during the test. Check for objects blocking vacuum to MAP sensor. An engine that is running poorly may cause this DTC to set.

DTC P0404: EGR POSITION SENSOR & DESIRED EGR POSITION IS MORE THAN 10 PERCENT

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM monitors EGR valve pintle position input to ensure that valve responds properly to commands from PCM. The PCM compares EGR position sensor with desired EGR position when valve is commanded open. If difference between EGR position sensor and desired EGR position is greater than 10 percent, this DTC will set.

Conditions for running DTC

1. Ignition voltage is greater than 11.7 volts.
2. Commanded EGR position is greater than zero percent.
3. EGR flow test is not active.
4. Desired EGR does not change greater than 20 percent.

Conditions for setting DTC

1. Vehicle must be driven.
2. Difference between desired EGR position and EGR position sensor is greater than 10 percent.
3. Condition is present for more than 13 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, command EGR valve from 0-100 percent. If EGR position sensor remains close to desired EGR position at all commanded positions, go to next step. If EGR position sensor does not remain close to desired EGR position at all commanded positions, go to step 4 .
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to next step. If DTC does not reset, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Using scan tool, observe EGR position sensor parameter. If scan tool indicates that EGR position sensor is at zero percent, go to step 7 . If scan tool does not indicate that EGR position sensor is at zero percent, go to next step.
5. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on, with engine off. Using scan tool, observe EGR position sensor parameter. If scan tool indicates that EGR position sensor is at zero percent, go to next step. If scan tool does not indicate that EGR position sensor is at zero percent, go to step 16 .
6. Turn ignition on, with engine off. Connect a test light between a known-good ground and EGR solenoid high control circuit (Red wire). Using scan tool, command EGR valve between zero and 10 percent. If test light turns on and off with each command, go to step 10 . If test light does not turn on and off with each command, go to step 9 .
7. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on, with engine off. Connect test light between a known-good ground and EGR solenoid high control circuit (Red wire). Using scan tool, command EGR valve between zero and 10 percent. If test light turns on and off with each command, go to next step. If test light does not turn on and off with each command, go to step 9 .
8. Connect test light between EGR solenoid high control circuit (Red wire) and low control circuit (White wire). Using scan tool, command EGR valve between zero and 10 percent. If test light turns on and off with each command, go to step 20 . If test light does not turn on and off with each command, go to step 15 .
9. If test light remains illuminated with each command, go to step 14 . If test light does not remain illuminate with each command, go to step 13 .
10. Check voltage from the EGR position sensor 5-volt reference circuit (Gray wire) to the low reference circuit (Black wire). If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 12 .
11. Connect a fused jumper between EGR position sensor 5-volt reference circuit (Gray wire) and signal circuit (Brown wire). If scan tool indicates that EGR position sensor value is about 100 percent, go to step 20 . If scan tool does not indicate that EGR position sensor value is about 100 percent, go to step 18 .
12. Using a DVOM, check voltage between a known-good ground and EGR position sensor 5-volt reference circuit (Gray wire). If voltage reading is about 5 volts, go to step 17 . If voltage reading is not about 5 volts, go to step 19 .
13. Turn ignition off. Check EGR solenoid high control circuit for a short to ground, high resistance or open circuit. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
14. Turn ignition off. Check EGR solenoid high control circuit for short to voltage. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
15. Turn ignition off. Check EGR solenoid low control circuit for open or high resistance. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
16. Turn ignition off. Check EGR valve position signal circuit for short to voltage. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
17. Turn ignition off. Check low reference circuit for open or high resistance. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
18. Turn ignition off. Check EGR valve position signal circuit for high resistance or short to ground. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
19. Turn ignition off. Check EGR position sensor 5-volt reference circuit for open, short to ground or short to voltage. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
20. Turn ignition off. Check for poor connections at EGR harness connector. Repair as necessary. After repairs, go to step 24 . If connections are okay, go to step 22 .
21. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 24 . If connections are okay, go to step 23 .
22. Replace EGR valve. After replacing EGR valve, go to step 24 .
23. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
24. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
25. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check for excessive deposits on EGR pintle or seat. Remove EGR valve and inspect for deposits that may interfere with EGR valve pintle extending completely or causing pintle to stick.

DTC P0405: EGR POSITION SENSOR SIGNAL VOLTAGE EXCESSIVELY LOW

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM monitors EGR valve pintle position input to ensure that valve responds properly to commands from PCM and to detect a fault if the pintle position sensor circuit is open or shorted. If PCM detect an excessively low EGR position sensor signal voltage, this DTC will set.

Conditions for running DTC

1. Ignition voltage is greater than 11.7 volts.
2. Engine is running.

Conditions for setting DTC

1. EGR position sensor voltage is less than 0.14 volt.
2. Conditions present for 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Using scan tool, observe EGR position sensor voltage parameter. If scan tool indicates that EGR position sensor voltage is less than 0.14 volt, go to step 4. If scan tool does not indicate that EGR position sensor voltage is less than 0.14 volts, go to next step.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to next step. If DTC does not reset, problem is intermittent.
4. Turn ignition off. Disconnect EGR valve harness connector. Connect a fused jumper wire between EGR valve harness connector terminals "C" (Brown wire) and "D" (Gray wire). (Scheme 5) Turn ignition on, with engine off. Using scan tool, observe EGR position sensor parameter. If scan tool indicates that EGR position sensor is about 100 percent, go to step 10. If scan tool does not indicate that EGR position sensor is about 100 percent, go to next step.
5. Disconnect fused jumper wire. Using a DVOM, check voltage between EGR valve harness connector terminals "B" (Black wire) and "D" (Gray wire). If voltage reading is about 5 volts, go to step 9. If voltage reading is not about 5 volts, go to next step.
6. Turn ignition off. Check for open or high resistance in Gray wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 15. If circuit is okay, go to next step.
7. Check for short to ground in 5-volt reference circuits from other components. See WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 15. If circuits are okay, go to next step.
8. Connect DVOM between EGR valve harness connector terminals "B" (Black wire) and "D" (Gray wire). Observe voltage while disconnecting all sensors, one at a time, that use a 5-volt reference signal. A change in voltage indicates the faulty component. Replace that component as necessary. After repairs, go to step 15. If no problem is found, go to step 11.
9. Turn ignition off. Check for short to ground, high resistance or open in Brown wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 15. If circuit is okay, go to step 11.
10. Turn ignition off. Check for short between Brown and Red wire at EGR valve harness connector. Repair as necessary. After repairs, go to step 15. If circuits are okay, go to step 12.
11. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 15. If connections are okay, go to step 14.
12. Check for poor connections at EGR valve harness connector. Repair as necessary. After repairs, go to step 15. If connections are okay, go to next step.
13. Replace EGR valve. After replacing EGR valve, go to step 15.
14. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing EGR, go to next step.
15. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
16. Using scan tool, observe the stored information and Capture info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0410: AIR INJECTION SYSTEM ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

An secondary Air Injection (AIR) pump is used to lower tailpipe emissions on start-up. The PCM supplies ground to AIR pump relay, which energizes AIR pump and AIR solenoid valve. Engine vacuum is applied to AIR shut-off valve when AIR solenoid is energized. The engine vacuum opens AIR shut-off valve which allows AIR to flow to exhaust manifolds.

PCM monitors the HO2S voltages to diagnose AIR system. During the AIR test, PCM activates the AIR pump during closed-loop operation. When AIR system is activated, PCM monitors the HO2S voltages and short term fuel trim values for both banks of the engine. If AIR system is operating properly, HO2S voltages should go low and short term fuel trim should go high.

If PCM determines that HO2S voltages for both banks did not respond as expected during the tests, DTC P0410 will set. If only one sensor responded, the PCM sets either a DTC P1415 or DTC P1416 to indicate on which bank the AIR system is inoperative.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0300, P0440, P0442, P0446, P0506 or P0507 is not set
2. Engine run time is more than 15 seconds after closed-loop operation.
3. Engine load is less than 33 percent.
4. Engine airflow is less than 18 grams/second.
5. Engine speed is greater than 750 RPM.
6. Ignition voltage is greater than 11.7 volts.
7. Air/fuel ratio is 13.1:1.
8. Engine coolant temperature is 158-230°F (70-110°C).
9. The intake air temperature is greater than 36°F (2°C).
10. Fuel system is not operating in power enrichment or Deceleration Fuel Cut-Off (DFCO) mode.
11. Short term fuel trim is 1.08.
12. Start-up ECT is less than 176°F (80°C).
13. Vehicle speed is greater than 25 MPH.

Conditions for setting DTC

1. HO2S voltage does not go less than 222 millivolts within 1.2 seconds when AIR pump turns on during closed-loop operation.
2. Short term fuel trim does not go greater than a predetermined amount when AIR pump turns on during closed-loop operation.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Observe AIR pump. If AIR pump runs constantly, go to step 25 . If AIR pump does not run constantly, go to next step.
3. Start and operate engine at idle for 5 minutes after closed-loop is achieved. Using scan tool, observe the long term fuel trim parameter. If long term fuel trim is greater than 10 percent, go to step 14 . If long term fuel trim is not greater than 10 percent, go to next step.
4. Turn ignition on, with engine off. Using scan tool, command AIR pump on and off. If AIR pump turns on and off, go to next step. If AIR pump does not turn on and off, go to step 6 .
5. Start and operate engine for 2 minutes. Ensure engine is at normal operating temperature and in closed-loop. Using scan tool, command AIR pump. Monitor HO2S 1 bank 1 and HO2S 1 bank 2 sensors. If HO2S 1 bank 1 and HO2S 1 bank 2 value decreases to 100 millivolts in 6 seconds, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If HO2S 1 bank 1 and HO2S 1 bank 2 value does not decrease to 100 millivolts in 6 seconds, go to step 15 .
6. Disconnect AIR pump harness connector. Using a test light connected to a known-good ground, probe Gray AIR pump harness connector C2 terminal "A" (Red wire). Using scan tool, command AIR pump on and off . If test light turns on and off, go to step 11 . If test light does not turn on and off, go to next step.
7. Turn ignition off. Remove vehicle battery. Remove AIR fuse block assembly near battery tray. Check AIR fuse. If fuse is open, go to step 28 . If fuse is okay, go to next step.
8. Reconnect battery cables. Using a test light connected to a known-good ground, probe AIR pump relay battery voltage circuit, switched side, at fuse block. If test light illuminates, go to next step. If test light does not illuminate, go to step 40 .
9. Turn ignition on. Using test light connected to a known-good ground, probe AIR pump relay ignition 1 voltage circuit, coil side, at fuse block. If test light illuminate, go to next step. If test light does not illuminate, go to step 41 .
10. Using test light connected to battery voltage, probe AIR pump relay control circuit. Using scan tool, command AIR pump relay on and off. If test light turns on and off, go to step 12 . If test light does not turn on and off, go to step 30 .
11. Using test light connected to battery voltage, probe AIR pump ground circuit. If test light illuminates, go to step 37 . If test light does not illuminate, go to step 45 .
12. Turn ignition off. Remove AIR pump relay (located in AIR fuse block). Connect a fused jumper between battery voltage circuit of AIR relay block and AIR pump supply voltage circuit at AIR fuse block. If AIR pump turns on, go to step 36 . If AIR pump does not turn on, go to next step.
13. Check open or high resistance in AIR pump battery supply voltage circuit between the AIR relay and AIR pump. If resistance is 0-5 ohms, go to step 37 . If resistance is not 0-5 ohms, go to step 43 .
14. Operate engine at 1500 RPM for one minute. If long term fuel trim is greater than 10 percent, diagnose fuel system. If long term fuel trim is not greater than 10 percent, go to next step.
15. Turn ignition off. Remove vacuum hose at the shut-off valve. Connect a hand-held vacuum pump to AIR shut-off valve and apply 10 in. Hg to AIR shut-off valve. If AIR shut-off valve holds vacuum for 30 seconds. go to next step. If AIR shut-off valve does not hold vacuum for 30 seconds, go to step 49 .
16. Connect a vacuum gauge to AIR shut-off vacuum hose. Start and operate engine at idle. If vacuum reading is zero in. Hg, go to next step. If vacuum reading is not zero in. Hg, go to step 50 .
17. Ensure vacuum gauge is still connected. Command AIR pump on and off. If vacuum reading increases to greater than 10 in. Hg and then drops back to zero in. Hg, go to step 31 . If vacuum reading does not increase to greater than 10 in. Hg and then drops back to zero in. Hg, go to next step.
18. Connect vacuum gauge to AIR solenoid outlet port. Command AIR pump on and off. If vacuum reading increases to greater than 10 in. Hg and drops back to zero inches, go to step 47 . If vacuum reading does not increases to greater than 10 in. Hg and drops back to zero inches, go to next step.
19. Remove vacuum hose at AIR solenoid inlet. Connect vacuum gauge to vacuum supply hose. Start and operate engine at idle. If vacuum reading is 10 in. Hg, go to step 21 . If vacuum reading is not 10 in. Hg, go to next step.
20. Remove vacuum check valve from vacuum supply hose. Connect vacuum gauge to hose. If vacuum reading is greater than 10 in. Hg, go to step 34 . If vacuum reading is not greater than 10 in. Hg, check for plugged vacuum source.
21. Using test light connected to ground, probe AIR solenoid supply voltage circuit. Using scan tool, command AIR pump on and off. If test light turns on and off, go to next step. If test light does not turn on and off, go to step 23 .
22. Using test light connected to battery voltage, probe AIR control solenoid ground circuit. If test light illuminates, go to step 38 . If test light does not illuminate, go to step 45 .
23. If AIR fuse is open, go to step 42 . If AIR fuse is okay, go to next step.
24. Turn ignition off. Check AIR solenoid supply voltage circuit for open or high resistance. Repair as necessary. After repairs, go to step 53 .
25. Turn ignition off. Remove AIR pump relay. Turn ignition on. If AIR pump runs constantly, go to next step. If AIR pump does not run constantly, go to step 27 .
26. Disconnect AIR pump harness connector. Using test light connected to a known-good ground, probe AIR pump supply voltage. If test light illuminates, go to step 44 . If test light does not illuminate, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
27. Using test light connected to battery voltage, probe AIR pump relay control circuit at fuse block. If test light illuminates, go to step 46 . If test light does not illuminate, go to step 48 .
28. Check battery voltage circuit between AIR fuse and AIR pump relay for short to ground. Repair as necessary. Replace AIR fuse as necessary. After repairs, go to step 53 . If circuit is okay, go to next step.
29. Check AIR pump supply voltage circuit for short to ground. Repair as necessary. Replace AIR fuse as necessary. After repairs, go to step 53 . If circuit is okay, go to step 51 .
30. Turn ignition off. Check AIR pump relay control circuit for open or short to voltage. Repair as necessary. After repairs, go to step 53 . If circuit is okay, go to step 39 .
31. Turn ignition off. Remove right side AIR crossover hose at right bank exhaust check valve. Turn ignition on. Using scan tool, command AIR pump on. If air pressure flows at crossover hose, go to step 34 . If air pressure does not flow at crossover hose, go to next step.
32. Remove crossover hose at AIR shut-off valve. Command the AIR pump on. If air pressure flows at the shut-off valve, go to step 34 . If air pressure does not flow at the shut-off valve, go to next step.
33. Remove outlet hose at AIR pump. Command AIR pump on. If air pressure flows at the pump outlet, go to next step. If air does not flow at the pump outlet, go to step 35 .
34. Check for leaks or restrictions in AIR shut-off valve, check valves, vacuum check valve fittings, AIR pipes and exhaust manifolds. Repair as necessary. After repairs, go to step 47 . If no problem is found, go to next step.
35. Check AIR inlet and outlet hoses for leaks or restrictions. Repair as necessary. After repairs, go to step 53 . If no problem is found, go to step 51 .
36. Check for poor connections at AIR pump relay block. Repair as necessary. After repairs, go to step 53 . If connections are okay, go to step 48 .
37. Turn ignition off. Check for poor connections at AIR pump harness connector. Repair as necessary. After repairs, go to step 53 . If connections are okay, go to step 51 .
38. Check for poor connections at AIR vacuum control solenoid harness connector. Repair as necessary. After repairs, go to step 53 . If connections are okay, go to step 50 .
39. Check for poor connections at PCM. Repair as necessary. After repairs, go to step 53 . If connections are okay, go to step 52 .
40. Repair open or short to ground in AIR pump relay battery voltage circuit. After repairs, go to step 53 .
41. Turn ignition off. Repair open or short to ground in AIR pump relay ignition 1 voltage circuit. Replace fuse as necessary. After repairs, go to step 53 . If circuit is okay, go to step 48 .
42. Repair short to ground in AIR solenoid supply voltage circuit. Replace AIR solenoid fuse as necessary. After repairs, go to step 53 .
43. Repair open, high resistance or short to ground in AIR pump supply voltage circuit. After repairs, go to step 53 .
44. Repair short to voltage in AIR pump supply voltage circuit. After repairs, go to step 53 .
45. Turn ignition off. Repair open or high resistance in AIR ground circuit. After repairs, go to step 53 .
46. Check for short to ground in AIR pump relay control circuit. After repairs, go to step 53 . If circuit is okay, go to step 52 .
47. Turn ignition off. Replace hoses or components as necessary. After repairs, go to step 53 .
48. Replace AIR pump relay. After replacing relay, go to step 53 .
49. Replace AIR shut-off valve. After replacing shut-off valve, go to step 53 .
50. Turn ignition off. Replace AIR vacuum control solenoid. After replacing solenoid, go to step 53
51. Replace AIR pump. After replacing AIR pump, go to step 53 .
52. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
53. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 3 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step.
54. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Using FREEZE FRAME/FAILURE RECORDS data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the FREEZE FRAME/FAILURE RECORDS data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail. Operate vehicle within the same FREEZE FRAME conditions, such as RPM, load, vehicle speed, temperature etc., observed. This will isolate when DTC failed.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

DTC P0418: SECONDARY AIR INJECTION PUMP & AIR SOLENOID CIRCUIT ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of driver is to supply ground for the controlled component. Each driver has a fault line which PCM monitors. When PCM commands a component on, voltage of control circuit should be low, near zero volts. When PCM commands control circuit to a component off, the voltage potential of the circuit should be high, about battery voltage. If fault detection circuit senses a voltage other than what the PCM expects, the fault line status changes causing DTC to set.

The relay controls the high current flow to the Secondary Air Injection (AIR) pump and AIR solenoid. This allows PCM driver to only have to control the relatively low current used by the relay.

Conditions for running DTC

1. Engine speed is greater than 400 RPM.
2. Ignition voltage is 6-18 volts.

Conditions for setting DTC

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

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, command the relay on and off. If relay turns on and off when commanded, go to next step. If relay does not turn on and off when commanded, go to step 5 .
3. Turn ignition off. Disconnect PCM harness connector C2. Install 5-amp fused jumper wire to control circuit at PCM harness connector. Turn ignition on, with engine off. Replace relay if DVOM goes to zero during the current draw test. Using DVOM, check current draw from relay control circuit in PCM harness connector to ground for 2 minutes. If current draw measures less than 0.75 amps, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If current draw does not measure less than 0.75 amps, go to next step.
4. Turn ignition off. Disconnect AIR pump relay. Check resistance from the relay control circuit in PCM harness connector to ground. If resistance is infinite resistance, go to step 12 . If resistance is not infinite, go to step 10 .
5. Turn ignition off. Disconnect relay. Connect test light between AIR pump relay control circuit and AIR pump relay ignition feed circuit, on coil side of the relay, at AIR pump relay harness connector. Turn ignition on, with engine off. Using scan tool, command relay on and off. If test light turns on and off when commanded, go to step 8 . If test light does not turn on and off when commanded, go to next step.
6. Using test light connected to ground, probe ignition feed circuit, located on coil side of relay, at AIR pump relay harness connector. If test light illuminated, go to next step. If test light does not illuminate, go to step 11 .
7. Turn ignition off. Reconnect relay. Disconnect PCM connector C2. Turn ignition on, with engine off. Using a fused jumper wire connected to ground, momentarily probe relay control circuit in PCM harness connector. If relay turns on when circuit is grounded and turns off when circuit is opened, go to step 9 . If relay does not turn on when circuit is grounded and or turn off when circuit is opened, go to step 10 .
8. Check connections at relay. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 12 .
9. Check connections at PCM. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 13 .
10. Repair faulty relay control circuit. After repairs, go to step 14 .
11. Repair faulty relay ignition feed circuit. After repairs, go to step 14 .
12. Replace the relay. After replacing relay, go to step 14 .
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
15. Using scan tool review the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Note. Remove any debris from PCM connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure that gaskets are installed correctly to prevent water intrusion into PCM.

This diagnostic only runs once per ignition cycle. A malfunction in HO2S heater circuits causes a DTC to set. Check HO2S heater circuits for intermittent opens and for poor connections. The HO2S wires provide supply of oxygen. Check the HO2S wires and connections for breaks or for contamination.

Using the FREEZE FRAME/FAILURE RECORDS may help to locate an intermittent condition. If DTC cannot be duplicated, the information included in the FREEZE FRAME/FAILURE RECORDS can help determine how many miles since the DTC set. The fail and pass counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. In order to isolate when DTC failed, operate vehicle within the same FREEZE FRAME conditions. These conditions include, RPM, vehicle load and vehicle speed.

DTC P0420 OR P0430: THREE-WAY CATALYTIC CONVERTER - LOW EFFICIENCY

Note. For circuit reference, see WIRING DIAGRAMS article.

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

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0171, P0172, P0200, P0300, P0335, P0336, P0341, P0342, P0343, P0351, P0401, P0404, P0405, P0410, P0418, P0440, P0442, P0443, P0446, P0449, P0500, P0502, P0503, P0506 , P0507, 0704, P0706, P0711, P0712, P0716, P0719, P0724, P0740, P0741, P0742, P0748, P0751, P0752, P0753, P0756, P0757, P0758, P1112, P1114, P1115, P1121, P1122, P1336, P1345, P1404, P1860, P1870 or P1875 is not set.
2. Engine operating longer than 400 seconds.
3. Engine coolant temperature is 158-248°F (70-120°C).
4. Intake air temperature is -15 to 167°F (5-75°C).
5. Engine speed is greater than 1300 RPM for a minimum of 9 seconds since the end of the last idle test.
6. Barometric pressure is greater than 74 kPa.
7. Fuel system is operating in closed-loop.

Conditions for setting DTC

1. PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Check if any other DTCs are present. Diagnose affected DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no other DTCs are set, go to next step.
3. Ensure correct OE three-way catalytic converter is installed. Check converter for dents, severe discoloration or holes. Ensure that oxygen sensors are properly installed and that wiring connections are properly retained and not damaged. Repair as necessary. After repairs, go to next step. If no problem is found, go to step 6 .
4. Replace catalytic converter. After replacing catalytic converter, go to step 6 .
5. Using scan tool, clear DTCs. Warm engine to normal operating temperature. Select DTC and SPECIFIC DTC function. Operate vehicle within conditions for setting this DTC and until scan tool indicates that this diagnostic test passed and ran. If scan tool indicates that this diagnostic passed, go to next step. If DTC resets, go to step 2 .
6. Select the Capture Info option and the Review Info option using the scan tool. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0440: EVAPORATIVE EMISSION SYSTEM ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

The Evaporative Emission (EVAP) large leak test applies vacuum to EVAP system and monitors vacuum decay. The control module monitors the Fuel Tank Pressure (FTP) sensor signal in order to determine the vacuum decay rate. At an appropriate time, control module turns EVAP canister purge solenoid on (open) and off (closed). This allows engine to draw a vacuum on EVAP system. At a calibrated time or vacuum level, the control module turns the purge solenoid off (closed) sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum. If system is unable to achieve the calibrated vacuum level or vacuum level decreases too rapidly, DTC will set.

Conditions for running DTC

1. DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1111, P1112, P1114, P1115, P1121 or P1122 is not set.
2. Ignition voltage is 10-18 volts.
3. Barometric pressure is greater than 75 kPa.
4. Fuel level is 15-85 percent.
5. Engine coolant temperature is 39-86°F (4-30°C).
6. Intake air temperature is 39-86°F (4-30°C).
7. Start up ECT and intake air temperature are within 16°F (9°C) of each other.
8. Vehicle speed is less than 75 MPH.

Conditions for setting DTC

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

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. If scan tool indicates that DTC P0443 or DTC P0449 is also set, diagnose affected DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If DTC P0443 or P0449 is not set, go to next step.
3. Turn ignition off. Check EVAP system for loose, missing or damaged service port valve, loose, incorrect, missing or damaged fuel fill cap. Check for damaged EVAP canister purge solenoid. Check disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses. Check for damaged EVAP canister vent solenoid or EVAP canister. Repair as necessary. After repairs, go to step 17 . If no problem is found, go to next step.
4. Turn ignition on, with engine off. Using scan tool, capture and record the Failure Records data and clear DTCs and perform Service Bay Check. If scan tool indicates that service bay test passed, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If scan tool does not indicate that service bay test passed, go to next step.
5. Turn ignition off. Always zero EVAP pressure and vacuum (in. H2O) gauges on EVAP Pressure/Purge Diagnostic Station (J-41413) before proceeding with diagnosis. Install Fuel Fill Cap Adaptor (J-41415-40) between diagnostic station and vehicle fuel fill cap. Turn ignition on, with engine off. Using scan tool, seal EVAP system. Using diagnostic station, pressurize system to 5 in. H2O. Rotate the rotary switch on diagnostic station to OFF/HOLD position. Monitor pressure gauge for one minute. If pressure is obtained, go to next step. If pressure cannot be obtained, go to step 8 .
6. Compare EVAP diagnostic station's value to scan tool's Fuel Tank Pressure (FTP) sensor value. If values are close to each other, go to next step. If values are not close to each other, go to step 13 .
7. Using EVAP diagnostic station, pressurize EVAP system to 5 in. H2O. Rotate the rotary valve to OFF/HOLD position. Monitor pressure gauge. Using scan tool, command EVAP canister purge solenoid to 50 percent. If EVAP system pressure decreases, go to step 9 . If EVAP system pressure does not decrease, go to step 10 .
8. Using EVAP diagnostic station, continuously pressurize EVAP system. Fuel tank may need to be partially lowered in order to inspect components located in upper portion of tank. Using Ultrasonic Leak Detector (J-41416), check for leaks in EVAP system purge pipe, vapor pipe, vent hose/pipe, fuel fill pipe/hose and fuel fill cap, canister, canister vent solenoid, canister purge solenoid, fuel sender assembly and/or seal. Check for leaks in FTP sensor seal, fill limiter canister vent solenoid, pressure relief valve, rollover valve, or fuel tank. Repair as necessary. After repairs, go to step 17 . If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
9. Disconnect EVAP canister purge pipe from EVAP canister purge solenoid. Install the vacuum hose from EVAP diagnostic station to EVAP canister purge solenoid port. Start and operate engine between 1200-1500 RPM. Using scan tool, command EVAP canister purge solenoid to 50 percent. If vacuum gauge is reading greater than 12 in. Hg, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If vacuum gauge is not reading greater than 12 in. Hg, go to step 15 .
10. Disconnect EVAP canister purge pipe from EVAP canister purge solenoid. If EVAP system pressure decreases, go to step 15 . If EVAP system pressure does not decrease, go to next step.
11. Disconnect purge pipe at EVAP canister. EVAP canister is located on top of fuel tank. If EVAP system pressure decreases, diagnose perform EVAP system cleaning. If EVAP system pressure does not decrease, go to next step.
12. Disconnect EVAP vapor line from EVAP canister (middle fitting on canister). If EVAP system pressure decreases, go to step 16 . If EVAP system pressure does not decrease, go to step 14 .
13. Replace FTP sensor. After replacing sensor, go to step 17 .
14. Repair pinched or obstructed EVAP vapor pipe. After repairs, go to step 17 .
15. Replace EVAP canister purge solenoid. After replacing purge solenoid, go to step 17 .
16. Replace EVAP canister. After replacing canister, go to next step.
17. Turn ignition on, with engine off. Using scan tool, perform Service Bay Check. If scan tool indicates service bay test passed, go to next step. If scan tool does not indicate service bay test passed, go to step 5 .
18. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Use EVAP Pressure/Purge Diagnostic Station (J-41413) in order to pressurize EVAP system to aid in locating intermittent leaks. Move all EVAP components while testing with Ultrasonic Leak Detector (J-41416). A temporary blockage in EVAP canister purge solenoid, purge pipe or EVAP canister could cause an intermittent condition. Repair blockage in EVAP system. Review the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often condition that caused DTC to be set occurs. This may assist in diagnosing the condition.

DTC P0442: EVAPORATIVE SYSTEM FAILS TO HOLD A PREDETERMINED LEVEL OF VACUUM

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM tests the Evaporative Emission (EVAP) system for large and small leaks, excess vacuum purge flow during non-commanded conditions, fuel level and fuel pressure sensor faults, and EVAP canister purge and canister vent solenoid faults. PCM monitors Fuel Tank Pressure (FTP) sensor in order to determine level of vacuum or pressure in EVAP system. PCM commands both EVAP canister purge solenoid and EVAP canister vent solenoid on when conditions for running the DTC are met in order to apply an engine vacuum to EVAP system. PCM commands EVAP canister purge solenoid off once system has reached a predetermined level of vacuum. The EVAP system should hold vacuum in sealed system. PCM sets this DTC in order to indicate a small leak if EVAP system fails to hold a predetermined level of vacuum for a predetermined length of time. This DTC sets after failing the test twice.

Conditions for running DTC

1. DTCs P0107, P0108, P0110, P0112, P0113, P0115, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0443, P0449, P0452, P0453, P1106, P1107, P1111, P1112, P1114, P1115, P1121 or P1122 is not set
2. Barometric pressure is greater than 75 kPa.
3. Fuel level is 15-85 percent.
4. Throttle position sensor angle is less than 75 percent.
5. Vehicle speed is less than 65 MPH.
6. Engine coolant temperature and intake air temperature 39-86°F (4-30°C).
7. Start-up engine coolant temperature and intake air temperature are within 16°F (9°C) of each other.

Conditions for setting DTC

1. Vacuum in EVAP system decays or leaks at too fast a rate.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. If scan tool indicates that DTC P0443 or P0449 is also set, diagnose affected DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If DTC P0443 or P0449 is not set, go to next step.
3. Check EVAP system for loose, missing or damaged service port dust cap and/or Schrader valve. Check for loose, incorrect, missing or damaged fuel fill cap. Check for damaged EVAP canister purge solenoid. Check for disconnected, improperly routed, kinked or damaged EVAP pipes and hoses. Check for damaged EVAP canister vent solenoid or canister. Repair as necessary. After repairs, go to step 6 . If no problem is found, go to next step.
4. Using scan tool, capture and record the fail record data and clear DTCs and perform Service Bay Test. If scan tool indicates that service bay test passed, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If scan tool does not indicate that service bay test passed, go to next step.
5. Install Fuel Fill Cap Adaptor (J-41415-40) between EVAP diagnostic station and fuel fill cap. Turn ignition on, with engine off. Using scan tool, seal EVAP system. Using EVAP diagnostic station, continuously pressurize EVAP system to 15 in. Hg. It may be necessary to partially lower fuel tank to inspect components located on upper portion of tank. Using Ultrasonic Leak Detector (J-41416), inspect for leaks in EVAP system purge pipe, vapor pipe, vent hose, fuel fill pipe/hose and fuel fill cap. Check for leaks in EVAP canister, canister vent solenoid, canister purge solenoid, fuel sender assembly and/or seal, FTP sensor seal, fill limiter vent valve, pressure relief valve, rollover valves, permanent EVAP pipes and/or fuel tank. Repair as necessary. After repairs, go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
6. Using scan tool, perform Service Bay Test. If scan tool indicates that service bay test passed, go to next step. If scan tool does not indicate service bay test passed, go to step 2 .
7. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Remove any debris from PCM harness connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure gaskets are installed correctly. The gaskets prevent water intrusion into PCM. An accurate indication of fuel level is required for PCM to properly pass or fail this DTC. Always diagnose fuel level sensor DTCs before performing this DTC test. Always inspect for fuel level sensor DTCs stored as history.

The service bay test may have to be performed in cold ambient air temperatures when vehicle is running a winter grade fuel. The scan tool displays a message when service bay test does not run. Check for charcoal release from vapor canister.

DTC P0443: EVAPORATIVE SYSTEM - INCORRECT VOLTAGE FOR THE COMMANDED STATE OF EVAP CANISTER PURGE SOLENOID DRIVER

Note. For circuit reference, see WIRING DIAGRAMS article.

The Evaporative Emission (EVAP) canister purge solenoid is Pulse Width Modulated (PWM). The PCM controls EVAP canister purge solenoid duty cycle by controlling amount of solenoid valve on time. The scan tool displays amount of on time as a percentage.

An ignition voltage is supplied directly to EVAP canister purge solenoid. PCM controls EVAP canister purge solenoid by grounding the control circuit using an internal switch called a driver. The primary function of the driver is to supply ground for the controlled component. PCM monitors the status of the driver. If PCM detects an incorrect voltage for the commanded state of the driver, DTC will set.

Conditions for running DTC

1. Engine speed is greater than 400 RPM.
2. System voltage is 6.0-18.0 volts.

Conditions for setting DTC

1. PCM detects that commanded state of the driver and actual state of control circuit does not match for 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, command EVAP canister purge solenoid to 50 percent and then to zero percent. If EVAP canister purge solenoid responds to commanded state, go to next step. If EVAP canister purge solenoid does not respond to commanded state, go to step 4 .
3. Review the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
4. Turn ignition off. Disconnect EVAP canister purge solenoid harness connector. Turn ignition on, with engine off. Using a test light connected to a known-good ground, probe EVAP canister purge solenoid harness connector terminal "A" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 11 .
5. Connect a test light between EVAP canister purge solenoid harness connector terminals. Using scan tool, command EVAP canister purge solenoid to 50 percent and then to zero percent. If test light turns on when EVAP canister purge solenoid is commanded to 50 percent and turns off when purge solenoid is commanded to zero percent, go to step 9 . If test light does not turn on when EVAP canister purge solenoid is commanded to 50 percent and/or does not turn off when purge solenoid is commanded to zero percent, go to next step.
6. If test light remains illuminated with each command, go to step 8 . If test light does not remain illuminated with each command, go to next step.
7. Turn ignition off. Check for open or short to voltage in Dark Green/White wire. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 10 .
8. Turn ignition off. Check for short to ground in Dark Green/White wire. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 13 .
9. Turn ignition off. Check for poor connections at EVAP canister purge solenoid harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 12 .
10. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 13 .
11. Turn ignition off. Repair open or short to ground in Pink wire to underhood fuse block. After repairs, go to step 14 .
12. Replace EVAP canister purge solenoid. After replacing solenoid, go to step 14 .
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate the vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
15. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0446: EVAPORATIVE SYSTEM - VACUUM DECAY RATE IS MORE THAN A PREDETERMINED VALUE

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM monitors the performance of the Evaporative Emission (EVAP) system by applying a predetermined level of vacuum to EVAP system, then monitors the vacuum decay rate. PCM sets this DTC if vacuum decay rate is more than a predetermined value.

Conditions for running DTC

1. DTCs P0107, P0108, P0110, P0112, P0113, P0115, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0442, P0443, P0449, P0452, P0453, P1106, P1107, P1111, P1112, P1114, P1115 P112 or P1122 is not set
2. Ignition voltage is 10-18 volts.
3. Barometric pressure is greater than 75 kPa.
4. Fuel level is 15-85 percent.
5. Engine coolant temperature and intake air temperature is 39-86°F (4-30°C).
6. Start-up engine coolant temperature and intake air temperature are within 16°F (9°C) of each other.

Conditions for setting DTC

1. The EVAP vacuum decay rate is more than a predetermined value for more than 2 seconds.
2. Vacuum present in EVAP system is greater than a predetermined value for more than 4 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. If DTC P0443, P0449, P0452 or P0453 is also set, diagnose affected DTCs first . See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If DTC P0443, P0449, P0452 or P0453 is not set, go to next step.
3. Check EVAP system for damaged EVAP canister vent solenoid or pinched EVAP fresh air vent hose, located on top of EVAP canister. Repair as necessary. After repairs, go to step 12 . If no problem is found, go to next step.
4. Using scan tool, review and record the FREEZE FRAME/FAILURE RECORDS data and clear DTCs, then perform Service Bay Test. If scan tool indicates that service bay test passed, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If scan tool does not indicate that service bay test passed, go to next step.
5. Disconnect vacuum line from EVAP canister purge solenoid. Turn ignition on, with engine off. Using scan tool, observe fuel tank pressure parameter. If scan tool indicates that fuel tank pressure is about zero in. H2O, go to next step. If scan tool does not indicate that fuel tank pressure is about zero in. H2O, go to step 10 .
6. Turn ignition off. Reconnect all previously disconnected hardware. Install EVAP Pressure/Purge Diagnostic Station (J-41413) and Fuel Tank Cap Adapter (J-41415). Turn ignition on, with engine off. Using scan tool, seal EVAP system. Using EVAP diagnostic station, pressurize EVAP system to 5 in. H2O. Disconnect EVAP vent hose from EVAP canister vent solenoid. If scan tool indicates that fuel tank pressure is about zero in. H2O, go to step 8 . If scan tool does not indicate that fuel tank pressure is about zero in. H2O, go to next step.
7. Using EVAP diagnostic station, maintain pressure at 5 in. H2O. Disconnect EVAP vapor pipe (middle hose on top if EVAP canister) from EVAP canister. If scan tool indicates that fuel tank pressure is about zero in. H2O, go to step 11 . If scan tool does not indicate that fuel tank pressure is about zero in. H2O, go to step 9 .
8. Turn ignition off. Replace EVAP canister vent solenoid. After replacing solenoid, go to step 12 .
9. Turn ignition off. Replace EVAP canister. After replacing EVAP canister, go to step 12 .
10. Turn ignition off. Replace fuel tank pressure sensor. After replacing sensor, go to step 12 .
11. Turn ignition off. Repair blockage in EVAP vent hose. After repairs, go to next step.
12. Reconnect all of EVAP hardware that was previously disconnected. Turn ignition on, with engine off. Using scan tool, perform Service Bay Test. If scan tool indicates that service bay test passed, go to next step. If scan tool does not indicate that service bay test passed, go to step 3 .
13. Using a scan tool, select the Review Info option. If scan tool indicate any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Remove any debris from PCM harness connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure gaskets are installed correctly. The gaskets prevent water intrusion into PCM. An accurate indication of fuel level is required for PCM to properly pass or fail this DTC. Always diagnose fuel level sensor DTCs before performing this DTC test. Always inspect for fuel level sensor DTCs stored as history.

The service bay test may have to be performed in cold ambient air temperatures when vehicle is running a winter grade fuel. The scan tool displays a message when service bay test does not run. Check for charcoal release from vapor canister.

DTC P0449: EVAPORATIVE SYSTEM - INCORRECT VOLTAGE FOR THE COMMANDED STATE OF EVAP CANISTER VENT SOLENOID DRIVER

Note. For circuit reference, see WIRING DIAGRAMS article.

An ignition voltage is supplied directly to the Evaporative Emission (EVAP) canister vent solenoid. The PCM controls EVAP canister vent solenoid by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply ground for the controlled component. PCM monitors status of the driver. If PCM detects an incorrect voltage for the commanded state of the driver, DTC will set.

Conditions for running DTC

1. Engine speed is greater than 400 RPM.
2. System voltage is 6.0-18.0 volts.

Conditions for setting DTC

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

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, command EVAP canister vent solenoid on and off. If EVAP canister vent solenoid turns on and off when commanded, go to next step. If EVAP canister vent solenoid does not turn on and off when commanded, go to step 4 .
3. Review the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
4. Turn ignition off. Disconnect EVAP canister vent solenoid harness connector. Turn ignition on, with engine off. Using a test light connected to a known-good ground, probe EVAP canister vent solenoid harness connector terminal "A" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 11 .
5. Connect test light between EVAP canister vent solenoid harness connector terminals. Using scan tool, command EVAP canister vent solenoid on and off. If test light turns on and off with each command, go to step 9 . If test light does not turn on and off with each command, go to next step.
6. If test light remains illuminated with each command, go to step 8 . If test light does not remain illuminated with each command, go to next step.
7. Turn ignition off. Check for short to voltage or open in White wire to PCM. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 10 .
8. Turn ignition off. Check for short to ground in White wire to PCM. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 10 .
9. Turn ignition off. Check for poor connections at EVAP canister vent solenoid harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 12 .
10. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to step 13 .
11. Turn ignition off. Repair open or short to ground in Pink wire to underhood fuse block. Replace fuse as necessary. After repairs, go to step 14 .
12. Replace EVAP canister vent solenoid. After replacing solenoid, go to step 14 .
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
15. Using scan tool, review the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

DTC P0452: FUEL TANK PRESSURE SENSOR CIRCUIT - LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative Emission (EVAP) diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as fuel tank pressure increases (positive pressure, low voltage). This DTC will set when FTP sensor signal is less than predetermined value.

DTC will run with engine running and will set when fuel tank pressure sensor voltage is less than 0.1 volt for more than 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Operate engine at idle for one minute. Using scan tool, monitor DTC information. If DTC P1639 fails this ignition, diagnose DTC P1639. Go to «DTC P1639»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p1639-5-volt-reference-2-circuit). If DTC P1639 is not set, go to next step.
3. Using scan tool, observe FTP sensor voltage. If FTP sensor voltage is less than 0.1 volt, go to step 5. If FTP sensor voltage is not less than 0.1 volt, go to next step.
4. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
5. Turn ignition off. Disconnect FTP sensor harness connector (sensor is located on top of fuel tank). Connect a fused jumper wire between FTP sensor harness connector terminals "B" (Dark Green wire) and "C" (Gray wire). (Scheme 7) Turn ignition on, with engine off. Using scan tool, observe FTP sensor voltage. If FTP sensor voltage is about 5 volts, go to step 8. If FTP voltage is not about 5 volts, go to next step.
6. Turn ignition off. Check for short to ground, high resistance or open in Gray wire between FTP sensor and PCM. Repair as necessary. After repairs, go to step 12. If circuit is okay, go to next step.
7. Check for short to ground, high resistance or open in Dark Green wire between FTP sensor and PCM. (Scheme 7) Repair as necessary. After repairs, go to step 12. If circuit is okay, go to step 9.
8. Turn ignition off. Check for poor connections at FTP sensor harness connector. After repairs, go to step 12. If connections are okay, go to step 10.
9. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 12. If connections are okay, go to step 11.
10. Replace FTP sensor. After replacing sensor, go to step 12.
11. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC resets, go to step 2. If DTC does not reset, go to next step.
13. Using scan tool, select the Capture Info option and Review Info option. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0453: FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative Emission (EVAP) diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as fuel tank pressure increases (positive pressure, low voltage). This DTC sets when FTP sensor signal is greater than predetermined value.

DTC will set when engine is running and fuel tank pressure sensor voltage is greater than 4.9 volts for more than 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Operate engine at idle for one minute. Using scan tool, monitor DTC information. If DTC P1635 and P1639 fails this ignition cycle, diagnose affected DTCs. Go to «DTC P1635 OR»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p1635-5-volt-reference-1-circuit) «P1639»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p1639-5-volt-reference-2-circuit). If DTC P1635 and P1639 does not fail this ignition cycle, go to next step.
3. Using scan tool, observe FTP sensor voltage. If FTP sensor voltage is greater than 4.3 volts, go to step 5. If FTP sensor voltage is not greater than 4.3 volts, go to next step.
4. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
5. Turn ignition off. Disconnect FTP sensor harness connector (sensor is located on top of fuel tank). Turn ignition on, with engine off. Using scan tool, observe FTP sensor voltage. If FTP sensor voltage is greater than zero volts, go to next step. If FTP sensor voltage is not greater than zero volts, go to step 7.
6. Check Dark Green wire between FTP sensor and PCM for short to voltage or short to Gray wire in FTP sensor circuit. Repair as necessary. After repairs, go to step 13. If circuit is okay, go to step 12.
7. Using a test light connected to battery voltage, probe FTP sensor harness connector terminal "A" (Black wire on "L" and "M" Series or Black/White wire on "S" and "T" Series). (Scheme 7) If test light illuminates, go to step 9. If test light does not illuminate, go to next step.
8. Check for open in Black wire ("L" and "M" Series) or Black/White wire ("S" and "T" Series). Repair as necessary. After repairs, go to step 13. If circuit is okay, go to step 10.
9. Check for poor connections at FTP sensor harness connector. Repair as necessary. After repairs, go to step 13. If connections are okay, go to step 11.
10. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 13. If connections are okay, go to step 12.
11. Replace FTP sensor. After replacing sensor, go to step 13.
12. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
13. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
14. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P0500: VEHICLE SPEED SENSOR (M/T ONLY)

Note. For circuit reference, see WIRING DIAGRAMS article.

The Vehicle Speed Sensor (VSS) assembly provides vehicle speed information to the PCM. The VSS assembly is a permanent magnet generator and produces an Alternating Current (AC) as the rotor teeth on output shaft of transmission (2WD) or transfer case (4WD) pass through the sensor's magnetic field. The frequency and amplitude of the AC waveform both increase as vehicle speed increases. If PCM detects no vehicle speed for a specified length of time while other sensors indicate that vehicle is moving, DTC will set.

DTC will set when

1. No MAP sensor DTCs P0106, P0107 or P0108.
2. No TP or APP sensor DTCs P0121, P0122, P0123, P1120, P1125, P1220, P1221, P1514, P1515, P1516, P1517, or P1518.
3. No crankshaft position sensor DTCs P0335 or P0336.
4. ECT is greater than 95°F (35°C).
5. TP sensor angle is 5-100 percent.
6. Engine speed greater than 1000 RPM.
7. MAP is 6-15 psi (40-100 kPa).
8. Conditions are present for 2 seconds and PCM detects no vehicle speed for 50 seconds.

1. Perform transmission diagnostic system check. See appropriate TRANSMISSION SERVICE & REPAIR manual. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, record the FAILURE RECORDS before clearing DTCs. Erase the FAILURE RECORDS from PCM using the CLEAR INFO function. Record the DTC FREEZE FRAME AND FAILURE RECORDS. Clear DTC. Raise and support the drive wheels. Start engine. Allow engine to idle in gear. If scan tool displays vehicle speed greater than zero MPH, go to next step. If scan tool does not display vehicle speed greater than zero MPH, go to step 4.
3. Turn off ignition. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME DATA and note parameters. Start engine. Operate vehicle within the FREEZE FRAME conditions and conditions for running this DTC. If scan tool displays vehicle speed greater than zero MPH, problem is intermittent. If scan tool does not display vehicle speed greater than zero MPH, go to next step.
4. Verify that latest calibration is installed in PCM. Update PCM with the latest calibration as necessary. If PCM required a calibration update, go to step 14. If PCM did not require a calibration update, go to next step.
5. Turn ignition off. Disconnect PCM harness connector. Using a DVOM, check resistance between PCM harness connector C2, terminals No. 20 (Light Green/Black wire) and No. 21 (Purple/White wire). (Scheme 2) If resistance 530-870 ohms, go to step 7. If resistance is not 530-870 ohms, go to next step.
6. Check VSS high (Purple/White wire) and low (Light Green/Black wire) signal circuits for open or high resistance, or for circuits that are shorted together. If a problem is found, repair as necessary. After repairs, go to step 14. If no problem is found, go to step 11.
7. Check resistance between ground and PCM harness connector C2, terminal No. 21. If resistance is greater than 50,000 ohms, go to step 10. If resistance is not greater than 50,000 ohms, go to next step.
8. Leave the DVOM connected between PCM harness connector C2, terminal No. 21 and ground. Disconnect VSS harness connector. Check resistance between ground and PCM harness connector C2, terminal 21. If resistance is greater than 50,000 ohms, go to step 11. If resistance is not greater than 50,000 ohms, go to next step.
9. Repair short to ground in VSS high signal circuit (Purple/White wire). After repairs, go to step 14.
10. Reconnect DVOM between PCM harness connector C2, terminals No. 20 and 21. Observe AC voltage on DVOM while rotating drive wheels by hand. If AC voltage is equals to or greater than 0.5 volt, go to step 13. If AC voltage is not equal to or greater than 0.5 volt, go to next step.
11. Remove VSS. Check VSS and VSS rotor for sensor or rotor damage, or excessive air gap between the VSS rotor and VSS. Check for incorrect alignment between VSS and VSS rotor. Repair or replace as necessary. After repairs, go to step 14. If not problem is found, go to next step.
12. Replace VSS. After replacing sensor, go to step 14.
13. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
14. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Ensure VSS is correctly torqued to transmission housing.

DTC P0506: IDLE SPEED - LOW

Note. For circuit reference, see WIRING DIAGRAMS article.

PCM controls idle speed with an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC valve in or out to vary amount of airflow into intake manifold and thus decrease or increase idle RPM. PCM commands IAC in counts. A higher count, allows more air to by-pass throttle plate (higher idle).

When ignition is off after an ignition cycle, PCM will first seat the IAC pintle in the air bypass bore and then retract pintle a predetermined amount of counts in order to allow the proper amount of air to bypass throttle plate for engine start-up. This procedure is known as an IAC reset.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0171, P0172, P0174, P0175, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0443, P0446, P0449, P1111, P1112, P1114, P1115, P1121, P1122, P1380, P1381, P1404 or P1441 is not set
2. Engine coolant temperature is greater than 140°F (60°C).
3. Barometric pressure is greater than 65 kPa.
4. Engine run time is greater than 60 seconds
5. Throttle position sensor is less than 0.7 percent.
6. VSS is less than one MPH.
7. Ignition voltage is 9-18 volts.
8. Intake air temperature is greater than 14°F (10°C).
9. Conditions are present for 2 seconds.

Conditions for setting DTC

1. Actual engine speed is 50 RPM less than the desired engine speed.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Set parking brake and block drive wheels. Start engine. Turn off all accessories. Using scan tool in RPM control function, slowly increment engine speed to 1800 RPM, then to 600 RPM, then to 1800 RPM. Exit the RPM control function. If engine speed stabilizes within 50 RPM of commanded RPM during the test, go to next step. If engine speed does not stabilize within 50 RPM of commanded RPM during the test, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails in this ignition cycle, go to next step. If DTC does not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J 37027-A) to IAC valve. Start engine. Using IAC motor driver, command IAC valve in until about 600 RPM is reached. Using IAC motor driver, command IAC valve out until about 1800 RPM is reached. Return engine speed to desired idle, as indicated on scan tool data list. If engine speed steadily decreases to about 600 RPM and steadily increases to about 1800 RPM when IAC valve was commanded in and out, go to next step. If engine speed does not steadily decreases to about 600 RPM and steadily increases to about 1800 RPM when IAC valve was commanded in and out, go to step 10.
5. Connect a Connector Test Adaptor Kit (J 35616-A) to IAC valve harness connector. Using a test light connected to ground, probe one of the IAC valve circuits at IAC valve harness connector test adaptor kit. Start engine. Using IAC Motor Driver (J 37027-A), command low RPM while observing a scan tool until IAC counts start to increment. Using IAC motor driver, command high RPM while observing scan tool until IAC counts start to increment. While IAC counts are incrementing, observe test light. Return engine idle speed to desired idle, as indicated on scan tool data list. Repeat procedure for the other 3 IAC valve circuits. If test light remains on and never flashing while IAC counts were incrementing at any of the IAC valve circuits during the test, go to step 9. If test light does not remain on and never flashing while IAC counts were incrementing at any of the IAC valve circuits during the test, go to next step.
6. If test light remains off and never flashing while IAC counts were incrementing at any of the IAC valve circuits during the test, go to step 8. If test light does not remain off and never flashing while IAC counts were incrementing at any of the IAC valve circuits during the test, go to next step.
7. Connect test light between IAC valve harness connector terminals "C" (Light Blue/Black wire) and "D" (Light Blue/White wire), using connector test adaptor kit. (Scheme 9) Using IAC motor driver, command low RPM while observing scan tool until IAC counts start to increment. Using IAC motor driver, command high RPM while observing scan tool until IAC counts start to increment. While IAC counts are incrementing, observe test light. Return engine idle speed to desired idle, as indicated on scan tool data list. Repeat procedure with test light connected between IAC valve harness connector terminals "A" (Light Green/Black wire) and "B" (Light Green/White wire). Return engine speed to desired idle, as indicated on scan tool data list. If test light stays illuminated and never flashing while IAC counts where incrementing during the test, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If test light does not stay illuminated and never flashing while IAC counts where incrementing during the test, go to step 14.
8. Turn ignition off. Disconnect PCM harness connectors. Using a DVOM, test for open or short to ground on IAC valve circuit where test light remained off. Repair as necessary. After repairs, go to step 15. If circuit is okay, go to step 11.
9. Turn ignition on, with engine off. Using a DVOM, check for short to voltage on IAC valve circuit where test light remained illuminated. Repair as necessary. After repairs, go to step 15. If circuit is okay, go to step 11.
10. Turn ignition off. Check for throttle body damage and tampering, or throttle lever screw tampering (if equipment), or restricted air intake system. Remove IAC valve. Check for clogged IAC passage, excessive deposits on throttle plate, excessive deposits in throttle bore or excessive deposits on IAC valve pintle. Repair as necessary. After repairs, go to step 15. If no problem is found, go to step 12.
11. Turn ignition off. Check for poor connection at PCM harness connectors. Repair as necessary. After repairs, go to step 15. If connections are okay, go to step 14.
12. Check for a poor connection at IAC valve harness connector. Repair as necessary. After repairs, go to step 15. If no problem is found, go to next step.
13. Replace IAC valve. After replacing IAC valve, go to step 15.
14. Turn ignition off. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
15. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
16. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check for restricted air intake system, incorrect operation and installation of all air intake components such as collapsed, clogged or loose air intake ducts, clogged air filter, and incorrect operation of MAF sensor. Check for a throttle stop screw that shows evidence of damage or tampering. Check throttle plate, throttle shaft, or throttle linkage that shows evidence of damage or tampering. Check for objects blocking IAC passage or throttle bore. Check for excessive deposits in IAC passage or IAC pintle, excessive deposits in throttle bore or throttle plate. Check for vacuum leaks, low or unstable idle condition caused by a non-IAC system condition that cannot be overcome by IAC valve.

DTC P0507: IDLE SPEED - HIGH

Note. For circuit reference, see WIRING DIAGRAMS article.

PCM controls idle speed with an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC valve in or out to vary amount of airflow into intake manifold and thus decrease or increase idle RPM. PCM commands IAC in counts. A higher count, allows more air to by-pass throttle plate (higher idle).

When ignition is turned on after an ignition cycle, PCM will first seat the IAC pintle in the air bypass bore and then retract pintle a predetermined amount of counts to allow the proper amount of air to bypass throttle plate for engine start-up. This procedure is known as an IAC reset.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0171, P0172, P0174, P0175, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0443, P0446, P0449, P1111, P1112, P1114, P1115, P1121, P1122, P1380, P1381, P1404 or P1441 is not set
2. Engine coolant temperature is greater than 140°F (60°C).
3. Barometric pressure is greater than 65 kPa.
4. Engine run time is more than 60 seconds.
5. TP sensor is less than 0.7 percent.
6. Vehicle speed is less than one MPH.
7. Ignition voltage is 9-18 volts.
8. Intake air temperature is greater than 14°F (-10°C).
9. Conditions are present for 2 seconds.

Conditions for setting DTC

1. Actual engine speed is 50 RPM greater than the desired engine speed.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. Set parking brake and block drive wheels. Start engine. Turn off all accessories. Using scan tool, select RPM control function and slowly increment engine speed to 1800 RPM, then to 600 RPM, then to 1800 RPM. Exit RPM control function. If engine speed stabilizes within 50 RPM of commanded RPM during the test, go to next step. If engine speed does not stabilize within 50 RPM of commanded RPM during the test, go to step 4 .
3. Observe the FREEZE FRAME/FAILURE RECORDS for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
4. Turn ignition off. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J 37027-A) to IAC valve. Start engine. Using IAC motor driver, command IAC valve in until about 600 RPM is reached. Using IAC motor driver, command IAC valve out until about 1800 RPM is reached. Return engine speed to desired idle as indicated on scan tool data list. If engine speed steadily decreases to about 600 RPM and steadily increase to about 1800 RPM when IAC valve was commanded in and out, go to next step. If engine speed does not steadily decreases to about 600 RPM and steadily increase to about 1800 RPM when IAC valve was commanded in and out, go to step 10 .
5. Connect Connector Test Adaptor Kit (J 35616-A). Using a test light connected to ground, probe one of the IAC valve circuits at the IAC valve harness connector using connector test adaptor kit. Start engine. Using IAC motor driver, command low RPM while observing scan tool until IAC counts start to increment. Using IAC motor driver, command high RPM while observing scan tool until IAC counts starts to increment. While IAC counts are incrementing, observe test light. Return engine idle speed to desired idle as indicated on scan tool data list. Repeat procedure for the other 3 IAC valve circuits. If test light remains on (never flashing) while IAC counts where incrementing at any of the IAC valve circuits during the test, go to step 9 . If test light does not remain on (never flashing) while IAC counts where incrementing at any of the IAC valve circuits during the test, go to next step.
6. If test light remains off (never flashing) while IAC counts where incrementing at any of the IAC valve circuits during the test, go to step 8 . If test light does not remain off (never flashing) while IAC counts where incrementing at any of the IAC valve circuits during the test, go to next step.
7. Connect test light between IAC valve harness connector terminals "C" (Light Blue/Black wire) and "D" (Light Blue/White wire) using IAC valve harness connector using IAC valve connector test adaptor kit. Using IAC motor driver, command low RPM while observing a scan tool until the IAC counts start to increment. Using IAC motor driver, command high RPM while observing scan tool until IAC counts starts to increment. While IAC counts are incrementing, observe test light. Return engine idle speed to desired idle as indicated on scan tool data list. Repeat procedure with test light connected between IAC valve harness connector terminals "A" (Light Green/Black) and "B" (Light Green/White wire). Return engine speed to desired idle as indicated on scan tool data list. If test light stays illuminated (never flashing) while the IAC counts where incrementing during the test, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If test light does not stay illuminated (never flashing) while the IAC counts where incrementing during the test, go to step 14 .
8. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground on IAC valve circuit where test light remained off. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 11 .
9. Turn ignition on, with engine off. Using a DVOM, check for short to voltage on IAC valve circuit where test light remained illuminated. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 11 .
10. Turn ignition off. Check throttle body for damage and tampering. Check throttle lever screw for tampering (if equipped). Check for vacuum leaks, faulty or incorrectly installed PCV valve and hose (if equipped), throttle shaft binding, throttle linkage, or cruise control linkage binding (if equipped). Remove IAC valve. Check for debris in IAC passage, excessive deposits on throttle plate, excessive deposits in throttle bore, or excessive deposits on IAC valve pintle. Repair as necessary. After repairs, go to step 15 . If no problem is found, go to step 12 .
11. Check for poor connection at PCM harness connectors. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to step 14 .
12. Check for poor connection at IAC valve harness connector. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to next step.
13. Replace IAC valve. After replacing IAC valve, go to step 15 .
14. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
15. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
16. Using scan tool, observe the stored information in Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Ensure throttle stop screw has not been tampered with. Check for a stuck IAC valve or throttle linkage. Reset IAC using scan tool MISC FUNCTIONS. Check if fuel system is running too rich or too lean. Check throttle body bore for foreign material.

DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681 OR P1683: CONTROL MODULE EEPROM

Note. For circuit reference, see WIRING DIAGRAMS article.

The Electrically Erasable Programmable Read Only Memory (EEPROM) contains data which is essential for operating the engine and transmission. The PCM continuously tests the integrity of this data.

Conditions for running DTC

1. Ignition switch in CRANK or RUN position.

Conditions for setting DTC

1. PCM is unable to correctly read the data from the flash memory.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
3. Operate engine at idle and warm to normal operating temperature. Using scan tool, select the DTC option and the Specific DTC option, then enter the DTC number on scan tool. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
4. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Replace PCM even if this DTC exists only as history DTC.

DTC P0650: MIL FAULT DETECTION CIRCUIT SENSES UNEXPECTED VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Ignition voltage is supplied directly to the Malfunction Indicator Light (MIL). The PCM controls the MIL by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage of the control circuit should be low (about zero volts). When PCM is commanding the control circuit to a component off, the voltage potential of the circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, the fault line status will change causing the DTC to set.

Conditions for running DTC

1. Engine speed is greater than 400 RPM.
2. Ignition voltage is 6-18 volts.

Conditions for setting DTC

1. PCM detects that the commanded state of the driver and actual state of control circuit do not match for a minimum of 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Verify whether Instrument Panel (IP) is operational. If IP is completely inoperative, diagnose instrument panel. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Turn ignition on, with engine off. Using scan tool, command MIL on and off. Repeat the commands as necessary. If MIL turns on and off when commanded, go to next step. If MIL does not turn on and off when commanded, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Check fuse that supplies voltage to MIL (RADIO BATT fuse located in passenger compartment fuse block on "L" and "M" Series or GAUGES fuse located in passenger compartment fuse block on "S" and "T" Series). If fuse is open, go to step 10. If fuse is okay, go to next step.
5. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. If MIL does not illuminate, go to next step. If MIL illuminates, go to step 11.
6. Turn ignition off. Remove fuse that supplies voltage to MIL. Turn ignition on, with engine off. Connect a DVOM between a known-good ground and PCM harness connector C2 terminal No. 46 (Brown/White wire). (Scheme 2) If voltage reading is zero volts, go to next step. If voltage reading is not zero volts, go to step 12.
7. Turn ignition off. Reinstall fuse. Turn ignition on, with engine off. Connect a fused jumper wire between ground and PCM harness connector C2 terminal No. 46 (Brown/White wire). Observe MIL. If MIL illuminates, go to step 15. If MIL does not illuminate, go to next step.
8. Turn ignition off. Remove IP assembly. On "L" and "M" Series, connect test light between a known-good ground and IP harness connector terminal B9 (Orange wire). On "S" and "T" Series, connect test light between a known-good ground and IP harness connector terminal A7 (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 13.
9. Check for open or high resistance in Brown/White wire between IP assembly and PCM. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 14.
10. Repair short to ground in Orange wire ("L" and "M" Series) or Pink wire ("S" and "T" Series) between IP assembly and fuse block. After repairs, go to step 18.
11. Repair short to ground in Brown/White wire between IP assembly and PCM. After repairs, go to step 18.
12. Turn ignition off. Repair short to voltage in Brown/White wire between IP assembly and PCM. After repairs, go to step 18.
13. Repair open in Orange wire ("L" and "M" Series) or Pink wire ("S" and "T" Series). After repairs, go to step 18.
14. Check for poor connections at IP assembly harness connector. Repair as necessary. After repairs, go to step 18. If connections are okay, go to step 16.
15. Turn ignition off. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 18. If connections are okay, go to step 17.
16. Replace IP assembly. After replacing IP assembly, go to step 18.
17. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
18. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step.
19. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Remove any debris from PCM connector surfaces before servicing PCM. Check PCM connector gaskets when diagnosing or replacing PCM. Ensure gaskets are installed correctly to prevent water intrusion into PCM.

If ignition feed circuit is suspected of being open, inspect for other lights on that circuit not illuminating. An open fuse causes the entire cluster to be inoperative. Also, if fuse is open, transmission DTCs will set. Using FREEZE FRAME/FAILURE RECORDS data may aid in locating an intermittent condition. If DTC cannot be duplicated, the information included in the FREEZE FRAME/FAILURE RECORDS data can be useful in determining how many miles since DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass or a fail. Operate vehicle within the same FREEZE FRAME conditions, such as RPM, load, vehicle speed, temperature, etc., that were noted. This will isolate when DTC failed.

DTC P0719: PCM DETECTS OPEN BRAKE SWITCH CIRCUIT DURING ACCELERATIONS

Note. For circuit reference, see WIRING DIAGRAMS article.

The brake switch indicates brake pedal status to PCM. The brake switch is a normally-closed switch that supplies battery voltage to Torque Converter Clutch (TCC) brake switch signal circuit to PCM. Applying brake pedal opens the switch, interrupting voltage to PCM. When brake pedal is released, PCM receives a constant voltage signal. If PCM receives a zero voltage signal at brake switch input and TCC is engaged, PCM de-energizes the TCC solenoid valve. The PCM disregards the brake switch input for TCC scheduling if there is a brake switch circuit fault.

DTC will set when PCM detects an open brake switch circuit (zero volts/low input) during accelerations.

Conditions for running DTC

1. No VSS assembly DTCs P0502 or P0503.
2. Ignition is on.

Conditions for setting DTC

1. PCM detects an open brake switch or circuit (zero volts) for 15 minutes without changing for 2 seconds and the following events occur 7 times; vehicle speed is less than 5 MPH, then vehicle speed is 5-20 MPH for 4 seconds, then vehicle speed is greater than 20 MPH for 6 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, record DTC Failure Records, then clear DTCs. Select TCC Brake Switch on scan tool. Disconnect brake switch harness connector. Using a test light connected to ground, connect test light to brake switch harness connector terminal "D" (Brown wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 4 .
3. Connect a fused jumper wire between brake switch harness connector terminals. Observe scan tool. If TCC brake switch status on scan tool changes from OPEN to CLOSED, go to step 7 . If TCC brake switch status on scan tool does not change from OPEN to CLOSED, go to step 9 .
4. Turn ignition off. On "L" and "M" Series, check BRAKE fuse in passenger compartment fuse block. On "S" and "T" Series, check ABS fuse in passenger compartment fuse block. If fuse is open, go to next step. If fuse is okay, go to step 8 .
5. Check for short to ground in Brown wire between brake switch and fuse block. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
6. Check for short to ground in Purple wire between brake switch and PCM. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 10 .
7. Turn ignition off. Replace brake switch. After replacing switch, go to step 11 .
8. Repair open in Brown wire between brake switch and fuse block. After repairs, go to step 11 .
9. Turn ignition off. Check for open in Purple wire between brake switch and fuse block. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
10. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
11. Verify repairs. Turn ignition on, with engine off. Using scan tool, select DTC and clear DTCs. Apply and release brake pedal. Verify that TCC Brake Switch status indicates CLOSED (12 volts) for 2 seconds. Using scan tool, select Specific DTC and enter this DTC. If DTC test runs and passes, system is okay. If DTC resets, go to step 1 .

DTC P0724: PCM DETECTS CLOSED BRAKE SWITCH CIRCUIT DURING DECELERATIONS

Note. For circuit reference, see WIRING DIAGRAMS article.

The brake switch indicates brake pedal status to PCM. The brake switch is a normally closed switch that supplies battery voltage on Torque Converter Clutch (TCC) brake switch signal circuit to PCM. Applying the brake pedal opens the switch, interrupting voltage to PCM. When brake pedal is released, PCM receives a constant voltage signal. If PCM receives a zero voltage signal at the brake switch input, and the TCC is engaged and PCM de-energizes TCC solenoid valve. PCM disregards brake switch input for TCC scheduling if there is a brake switch circuit fault.

Conditions for running DTC

1. No VSS assembly DTCs P0502 or P0503.
2. Ignition is on.

Conditions for setting DTC

1. PCM detects a closed brake switch circuit (12 volts) without changing for 2 seconds and the following events occur 7 times: vehicle speed is greater than 20 MPH for 6 seconds; then vehicle speed is 5-20 MPH for 4 seconds; then vehicle speed is less than 5 MPH.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, record DTC failure records, then clear DTCs. Select TCC brake switch on scan tool. Disconnect brake switch connector from brake switch. Observe scan tool. If TCC brake switch status on scan tool change from CLOSED to OPEN, go to next step. If TCC brake switch status on scan tool does not change from CLOSED to OPEN, go to step 4.
3. Turn ignition off. Replace brake switch. After replacing brake switch, go to step 6.
4. Turn ignition off. Check for short to power in Purple wire between brake switch and PCM harness connector C1 terminal No. 33. (Scheme 2) Repair as necessary. After repairs, go to step 6. If circuit is okay, go to next step.
5. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
6. Turn ignition on, with engine off. Using scan tool, select clear DTC. Apply and release brake pedal. Verify that the TCC brake switch status indicates OPEN (zero volts) for 2 seconds. Select Specific DTC. Enter this DTC. If DTC test runs and passes, system is okay. If DTC resets, go to step 2.

DTC P1111: IAT SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor measures temperature of air entering engine. The PCM supplies 5 volts to the IAT signal circuit. When IAT sensor is cold, sensor resistance is high. When air temperature increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on IAT signal circuit. With lower sensor resistance, PCM detects a lower voltage on IAT signal circuit. If PCM detects an intermittent high IAT signal voltage, indicating a low temperature, this DTC will set .

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0125, P0128, P0502, P0503, P1114 and P1115 is not set
2. Engine run time is more than 120 seconds.
3. Engine coolant is greater than 140°F (60°C).
4. Vehicle is less than 7 MPH.
5. Mass airflow is less than 15 grams/second.

Conditions for setting DTC

1. Intake air temperature is less than -38°F (-39°C) for more than one second.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Observe DTC information on scan tool. If DTC P0113 is set, go to «DTC P0113»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0113-intake-air-temperature-sensor). If DTC P0113 is not set, go to next step.
3. Turn ignition off. Disconnect IAT sensor harness connector. Check for poor connection at IAT sensor harness connector. Repair as necessary. After repairs, go to step 8. If connections are okay, go to next step.
4. Check for intermittent open in Tan wire between IAT sensor harness connector terminal "B" and PCM harness connector C2 terminal No. 25 ("L" and "M" Series) or PCM harness connector C1 terminal No. 57 ("S" and "T" Series). (Scheme 2) Repair as necessary. After repairs, go to step 8. If circuit is open, go to next step.
5. Check for intermittent short to another voltage source in Tan wire between IAT sensor harness connector terminal "B" and PCM harness connector C2 terminal No. 25 ("L" and "M" Series) or PCM harness connector C1 terminal No. 57 ("S" and "T" Series). (Scheme 2) Repair as necessary. After repairs, go to step 8. If circuit is okay, go to next step.
6. Check for intermittent open in Black wire between IAT sensor harness connector terminal "A" and PCM harness connector terminal No. 25. Repair as necessary. After repairs, go to step 8. If circuit is okay, go to next step.
7. Disconnect PCM harness connector. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to next step. If connections are okay, problem is intermittent.
8. Turn ignition on, with engine off. Using scan tool, clear DTC's. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
9. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P1112: IAT SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor measures temperature of air entering engine. The PCM supplies 5 volts to the IAT signal circuit. When IAT sensor is cold, sensor resistance is high. When air temperature increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on IAT signal circuit. With lower sensor resistance, PCM detects a lower voltage on IAT signal circuit. If PCM detects an intermittent low IAT signal voltage, indicating a high temperature, this DTC will set.

Conditions for running DTC

1. DTC P0500, P0502 or P0503 is not set.
2. Engine run time is more than 45 seconds.
3. Vehicle speed is greater than 25 MPH.

Conditions for setting DTC

1. Intake air temperature is greater than 282°F (139°C).
2. Condition exists for more than 6 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, observe DTC information. If DTC P0112 is set, go to «DTC P0112»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0112-intake-air-temperature-sensor). If DTC P0112 is not set, go to next step.
3. Turn ignition off. Check for an intermittent short to ground in Tan wire between IAT sensor harness connector terminal "B" and PCM harness connector C2 terminal No. 25 ("L" and "M" Series) or PCM harness connector C1 terminal No. 57 ("S" and "T" Series). (Scheme 2) Repair as necessary. After repairs, go to next step. If circuit is okay, problem is intermittent.
4. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
5. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P1114: ECT SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. The PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively low ECT signal voltage, which is a high temperature indication, this DTC will set.

Conditions for running DTC

1. Engine run time is more than 5 seconds.

Conditions for setting DTC

1. PCM detects an intermittent high ECT sensor temperature while engine is running and run time exceeds 5 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Start engine. Observe scan tool. If scan tool indicates that DTC P0117 also failed, go to «DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0117-engine-coolant-temperature-sensor) . If DTC P0117 is not set, go to next step.
3. Turn engine off. Turn ignition on with engine off. Using a scan tool, observe ECT sensor temperature while moving sensor connector and PCM connector. If scan tool indicates an abrupt change in value, go to step 6 . If scan tool does not indicate an abrupt change in value, go to step 4 .
4. Using scan tool, observe ECT sensor temperature while moving wiring harness at sensor and PCM. If scan tool indicates an abrupt change in value, go to step 7 . If scan tool does not indicate an abrupt change in value, go to next step.
5. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC does not reset, system is okay.
6. Turn ignition off. Repair connector or terminal as necessary. After repairs, go to step 8 .
7. Turn ignition off. Repair harness or wiring as necessary. After repairs, go to next step.
8. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate the vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to step 3 . If DTC does not reset, go to next step.
9. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check for short to ground in ECT sensor harness connector signal circuit. Observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor. See appropriate SENSOR OPERATING RANGE CHARTS article.

DTC P1115: ECT SENSOR CIRCUIT INTERMITTENT HIGH VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Engine Coolant Temperature (ECT) sensor is a thermistor or a variable resistor, that varies resistance based on temperature. As temperature of sensor increases, resistance decreases. Low temperature will result in a high signal voltage. DTC will set when PCM sees an ECT sensor voltage of greater than 5 volts.

Conditions for running DTC

1. Engine run time is more than 5 seconds.

Conditions for setting DTC

1. The PCM detects an intermittent low ECT sensor temperature while the engine is running and run time exceeds 5 seconds

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, check DTCs. If DTC P0118 is also set, go to «DTC P0118»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0118-engine-coolant-temperature-sensor) . If DTC P0118 is not set, go to next step.
3. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature while moving sensor connector and PCM connector. If scan tool indicates an abrupt change in value, go to step 6 . If scan tool does not indicate an abrupt change in value, go to next step.
4. Using scan tool, observe ECT sensor temperature while moving wiring harness at sensor and PCM. If scan tool indicates an abrupt change in value, go to step 7 . If scan tool does not indicate an abrupt change in value, go to next step.
5. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to the FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC does not reset, system is okay.
6. Turn ignition off. Repair connector or terminal as necessary. After repairs, go to step 8 .
7. Turn ignition off. Repair harness or wiring as necessary. After repairs, go to next step.
8. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC resets, go to step 2 . If DTC does not reset, go to next step.
9. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check for short to ground in ECT sensor harness connector signal circuit. Observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor. See appropriate SENSOR OPERATING RANGE CHARTS article.

DTC P1121: THROTTLE POSITION SENSOR CIRCUIT INTERMITTENT & EXCESSIVELY HIGH SIGNAL VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Throttle Position (TP) sensor measures amount throttle opening. PCM uses TP sensor information for fuel delivery calculations. TP sensor readings during acceleration are much higher than those during deceleration or idle. DTC will set when PCM detects an intermittent and excessively high signal voltage while engine is running.

Conditions for running DTC

1. Ignition is on.
2. DTC P1635 or P1639 is not set.

Conditions for setting DTC

1. TP sensor intermittently indicates a throttle position signal of greater than 4.9 volts.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Turn ignition off. Disconnect TP sensor harness connector. Connect a DVOM between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series) and "B" (Black wire). (Scheme 4) Turn ignition on, with engine off. Lightly touch and move the related engine wiring harnesses and connectors for all 5-volt reference circuits while observing voltage on DVOM. Any change in voltage indicates area where a short to voltage may be found. Repair as necessary. After repairs, go to step 9. If no problem is found, go to next step.
3. Turn ignition off. Check for an intermittent short to voltage in Dark Blue wire between TP sensor harness connector "C" and PCM harness connector C2 terminal No. 24. (Scheme 2) Turn ignition off. Connect DVOM between TP sensor harness connector terminals "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series) and "C" (Dark blue wire). Turn ignition on, with engine off. Lightly touch and move the related engine wiring harnesses and connectors while observing voltage on DVOM. Any change in voltage indicates the area where a short to voltage may be found. Repair as necessary. After repairs, go to step 9. If no problem is found, go to next step.
4. Turn ignition off. Check for an intermittent open or high resistance in Black wire between TP sensor harness connector "B" and PCM harness connector C1 terminal No. 60. Turn ignition off for 30 seconds. Connect DVOM between TP sensor harness connector terminals "B" (Black wire) and "C" (Dark Blue wire). Lightly touch and move the related engine wiring harnesses and connectors while observing resistance on DVOM. Any change in resistance indicates the area where an open or a high resistance may be found. Repair as necessary. After repairs, go to step 9. If no problem is found, go to next step.
5. Check for faulty connections at TP sensor harness connector. Repair as necessary. After repairs, go to step 9. If connections are okay, go to next step.
6. Check for faulty connections at PCM harness connector. Repair as necessary. After repairs, go to step 9. If connections are okay, go to next step.
7. Connect 2 fused jumper wires at TP sensor, one at TP sensor harness connector terminal "C" (Dark Blue wire) and one at terminal "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series). Using DVOM set to 40K ohms scale, connect DVOM to jumper wires. Press the MIN MAX button on DVOM. Slowly depress accelerator pedal to WOT position and back to closed throttle position several times. Press MIN MAX button and record MAX reading. Press MIN MAX button again and record MIN reading. Remove jumper from terminal "A" and connect jumper to terminal "B" (Black wire). Repeat steps 2-7. If a MAX value of OL or a MIN value of zero ohms is recorded in either test, go to next step. If a MAX value of OL or a MIN value of zero ohms is not recorded in either test, problem is intermittent.
8. Replace TP sensor. After replacing TP sensor, go to next step.
9. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
10. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCS are displayed, system is okay.

DTC P1122: THROTTLE POSITION SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

Note. For circuit reference, see WIRING DIAGRAMS article.

Throttle Position (TP) sensor measures amount of throttle opening. PCM uses TP sensor information for fuel delivery calculations. TP sensor readings during acceleration are much higher than those during deceleration or idle. DTC will set when PCM detects an intermittent low TP sensor voltage while engine is running.

Conditions for running DTC

1. Ignition is on.
2. DTC P1635 or P1639 is not set.

Conditions for setting DTC

1. TP sensor intermittently indicates a throttle position signal of less than 0.15 volt.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Turn ignition off. Disconnect TP sensor harness connector. Connect a DVOM between TP sensor harness connector terminals "A" (Black wire in "L" and "M" Series; Gray wire on "S" and "T" Series) and "C" (Dark Blue wire). (Scheme 2)and (Scheme 4). Turn ignition on. Lightly touch and move the related engine wiring harnesses and connectors for all of the 5-volt reference circuits while observing voltage on DVOM. Any change in voltage indicates the area where a 5-volt reference circuit fault may be found. Repair as necessary. After repairs, go to step 8. If no problem is found, go to next step.
3. Reconnect TP sensor harness connector. Using scan tool, observe TP voltage parameter. Lightly touch and move the related engine wiring harnesses and connectors for the TP signal circuit (terminal "C") while observing voltage. Any change in voltage indicates the area where a TP signal circuit fault may be found. Repair as necessary. After repairs, go to step 8. If no problem is found, go to next step.
4. Check for faulty connections at TP sensor harness connector. Repair as necessary. After repairs, go to step 8. If connections are okay, go to next step.
5. Check for faulty connections at PCM harness connector. Repair as necessary. After repairs, go to step 8. If connections are okay, go to next step.
6. Using 2 fused jumpers, connect one jumper wire to TP sensor harness connector terminal "C" (Dark Blue wire) and one at TP sensor harness connector terminal "A" (Black wire on "L" and "M" Series; Gray wire on "S" and "T" Series). (Scheme 4) Using a DVOM set to 40K ohms scale, connect DVOM to jumper wires. Press the MIN MAX button on DVOM. Slowly depress accelerator pedal to WOT position and back to closed throttle position several times. Press MIN MAX button and record MAX reading. Press MIN MAX button again and record MIN reading. Remove jumper from terminal "A". Connect jumper to TP sensor harness connector terminal "B" (Black wire) and repeat steps 2-7. If a MAX value of OL or a MIN value of zero ohms is recorded in either test, go to next step. If a MAX value of OL or a MIN value of zero ohms is not recorded in either test, problem is intermittent.
7. Replace TP sensor. After replacing sensor, go to next step.
8. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Does DTC test runs and passes, go to next step. If DTC resets, go to step 2.
9. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P1133 OR P1153: HEATED OXYGEN SENSOR - INSUFFICIENT SWITCHING ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) creates a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S is functioning properly. DTC checks for an adequate number of HO2S voltage transitions greater than or less than the bias range of 300-600 millivolts. This DTC sets when PCM fails to detect a minimum number of voltage transitions greater than or less than the bias range during the test period.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set.
2. Engine coolant temperature is greater than 135°F (57°C).
3. Engine run time is more than 160 seconds.
4. Mass airflow is 15-55 grams/second.
5. Engine speed is 1100-3000 RPM.
6. Throttle position is greater than 5 percent.
7. System operating in closed-loop.
8. The ignition 1 signal is 9-18 volts.
9. Fuel tank level remaining is more than 10 percent.
10. Intrusive tests are not in progress.
11. Scan tool output controls are not active.
12. Conditions are met for 100 seconds.

Conditions for setting DTC

1. HO2S lean-to-rich and rich-to-lean switches are less than a calibrated value.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, check for HO2S related DTCs. If any other HO2S DTCs are set, go to step 4. If no other HO2S DTCs are set, go to next step.
3. Check for PCM related DTCs. If other DTCs are set, diagnose affected DTC first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no other DTCs are set, go to step 5.
4. Turn ignition off. Repair cause of HO2S silicon contamination, leading, incorrect gasket sealer, rich fuel mixture or antifreeze contamination. Replace HO2S. After replacing sensor, go to next step 18.
5. Using scan tool, store DTC information from PCM into scan tool. Clear DTC information from PCM. Start and warm engine to normal operating temperature. Operate engine under the conditions for setting this DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If this DTC ran and failed this ignition cycle, go to step 7. If this DTC did not run or did not fail this ignition cycle, go to next step.
6. Check for exhaust system leak between engine and HO2S, poor HO2S terminal contact, improperly torqued HO2S, faulty HO2S, poor PCM connector terminal contact. Check HO2S high or low circuit for intermittent open or short, or excessive resistance. Check for contaminated HO2S. Repair as necessary. After repairs, go to step 18. If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
7. Check exhaust system for leaks between engine and HO2S. Check HO2S and PCM connectors for proper terminal contact. Repair as necessary. After repairs, go to step 18. If no problem is found, go to next step.
8. Turn ignition off. Disconnect affected HO2S harness connector. Using a jumper wire connected to ground, jumper HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6) Using scan tool, monitor HO2S voltage. If scan tool voltage reading is 351-551 millivolts, go to next step. If scan tool voltage reading is not 351-551 millivolts, go to step 13.
9. Connect jumper wire between ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). Monitor HO2S voltage. If scan tool voltage reading is 20 millivolts, go to next step. If scan tool voltage reading is not 20 millivolts, go to step 14.
10. Remove jumper wire. Using a test light connected to a known-good ground, probe HO2S harness connector terminal "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 15.
11. Connect test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 16.
12. Repair cause of HO2S contamination before replacing HO2S sensor. After replacing sensor, go to step 17.
13. Check for short between each HO2S circuits. Repair as necessary. After repairs, go to step 18. If circuits are okay, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
14. Check for open or short in Purple/White or Purple wires between HO2S and PCM. Check for open or short in Tan/White or Tan wires between HO2S and PCM. Repair as necessary. After repairs, go to step 18.
15. Repair HO2S heater ignition feed circuit (Pink wire). After repairs, go to step 18.
16. Repair HO2S heater ground circuit (Brown wire). After repairs, go to step 18.
17. Replace HO2S. After replacing sensor, go to next step.
18. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate engine within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
19. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check HO2S heater operation. Never solder HO2S wire. An intermittent may be caused by poor connection, rubbed-through wire insulation or broken wire inside insulation.

DTC P1133 OR P1153: HEATED OXYGEN SENSOR - INSUFFICIENT SWITCHING ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if HO2S is functioning properly. DTC checks for an adequate number of HO2S voltage transitions greater than or less than the bias range of 300-600 millivolts. This DTC sets when PCM fails to detect a minimum number of voltage transitions greater than and less than the bias range during the test period.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine coolant temperature is greater than 135°F (57°C).
3. Engine run time is more than 160 seconds.
4. Mass airflow is 15-55 grams/second.
5. Engine speed is 1100-3000 RPM.
6. Throttle position is greater than 5 percent.
7. System operating in closed-loop.
8. The ignition 1 signal is 9-18 volts.
9. Fuel tank level remaining is more than 10 percent.
10. Intrusive tests are not in progress.
11. Scan tool output controls are not active.
12. Conditions are met for 100 seconds.

Conditions for setting DTC

1. HO2S lean-to-rich and rich-to-lean switches are less than a calibrated value.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Operate engine at idle and warm engine to normal operating temperature. Operate vehicle within the parameters specified in the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Using scan tool, monitor the DTC information. If DTC P1133 or P1153 fails this ignition cycle, go to next step. If DTC P1133 or P1153 does not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
3. If both DTC P1133 and P1153 fails this ignition cycle, go to step 8. If DTC P1133 and P1153 did not fail this ignition cycle, go to next step.
4. Check for an exhaust system leak. If an exhaust leak is found, repair as necessary. After repairs, go to step 14. If no exhaust leak is found, go to next step.
5. Check if HO2S is securely installed. Check for corrosion on terminals, or terminal tension at HO2S and PCM. Check for damaged wiring. Repair as necessary. After repairs, go to step 14. If no problem is found, go to next step.
6. Disconnect HO2S harness connector. Connect a jumper wire between a known-ground and HO2S harness connector terminal "B" (Tan/White or Tan wire). (Scheme 6)or see scheme 7. Using scan tool in Engine 1 Data List, monitor HO2S voltage. If scan tool indicates a voltage that is within 350-550 millivolts, go to next step. If scan tool does not indicate a voltage that is within 350-550 millivolts, go to step 10.
7. Connect 2 jumper wires between battery ground and to HO2S harness connector terminals "A" (Tan/White or Tan wire) and "B" (Purple/White or Purple wire). Using scan tool, monitor HO2S voltage. If voltage reading is less than 200 millivolts, go to step 13. If voltage reading is not less than 200 millivolts, go to step 9.
8. Turn ignition off. Determine and correct the cause of HO2S contamination before replacing a sensor. Check for fuel contamination, improper use of RTV sealant, or excessive engine oil or coolant consumption. Replace affected HO2S. After replacing HO2S, go to step 14.
9. Remove jumper wire from HO2S harness connector terminal "A". Using a DVOM, check voltage between battery ground and HO2S harness connector terminal "A". If voltage reading is about 5 volts, go to step 12. If voltage reading is not about 5 volts, go to step 11.
10. Turn ignition off. Repair for short to ground or short to voltage in Purple/White or Purple wire between HO2S and PCM. After repairs, go to step 14.
11. Turn ignition off. Repair open on Tan/White or Tan wire between HO2S and PCM. If circuit is okay, repair faulty PCM connections. After repairs, go to step 14.
12. Turn ignition off. Repair open in Purple/White or Purple wire between HO2S and PCM. If circuit is okay, repair faulty PCM connections. After repairs, go to step 14.
13. Turn ignition off. Replace appropriate HO2S. After replacing HO2S, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool, observe the stored information and Capture info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check HO2S heater operation. Never solder HO2S wire. An intermittent may be caused by poor connection, rubbed-through wire insulation or broken wire inside insulation.

DTC P1134 OR P1154: HEATED OXYGEN SENSOR TRANSITION TIME RATIO NOT WITHIN CALIBRATED RANGE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if the difference in transition times from lean-to-rich or rich-to-lean has exceeded a maximum ratio. PCM monitors the time needed for HO2S to transition from greater than 600 millivolts to less than 300 millivolts and vice versa. If either of these times are longer than the other by a calibrated ratio, DTC will set.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine coolant temperature is greater than 135°F (57°C).
3. Engine run time is more than 160 seconds.
4. Mass airflow sensor is 15-55 grams/second.
5. Engine speed is 1100-3000 RPM.
6. Throttle position is greater than 5 percent.
7. System is operating in closed-loop status.
8. Ignition 1 signal is 9-18 volts.
9. Fuel tank level remaining is more than 10 percent.
10. Scan tool output controls are not active.
11. Conditions are met for 100 seconds.

Conditions for setting DTC

1. HO2S transition time ratio is not within a calibrated range.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Check for HO2S related DTCs. If any other HO2S DTCs are set, go to step 4. If no other HO2S DTCs are set, go to next step.
3. Check for PCM related DTCs. If PCM DTCs are set, diagnose affected DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no PCM DTCs are set, go to step 5.
4. Repair cause of HO2S silicon contamination, leading, incorrect gasket sealer, rich fuel mixture or antifreeze contamination. Replace HO2S. After replacing sensor, go to next step 18.
5. Using scan tool, check and record DTC information. Clear DTCs. Start and warm engine to normal operating temperature. Operate engine under the conditions for setting this DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If this DTC ran and failed this ignition cycle, go to step 7. If this DTC did not run or did not fail this ignition cycle, go to next step.
6. Check for exhaust system leak between engine and HO2S, poor HO2S terminal contact, improperly torqued HO2S, faulty HO2S, poor PCM connector terminal contact. Check HO2S high or low circuit for intermittent open or short, or excessive resistance. Check for contaminated HO2S. Repair as necessary. After repairs, go to step 18. If no problems were found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
7. Check exhaust system for leaks between HO2S and engine. Repair exhaust as necessary. Check HO2S and PCM connectors for correct terminal contact. Repair as necessary. After repairs, go to step 18. If no problem is found, go to next step.
8. Turn ignition off. Disconnect affected HO2S harness connector. Using a jumper wire connected to ground, jumper HO2S harness connector terminal "A" (Tan/White or Tan wire). (Scheme 6) Using scan tool, monitor HO2S voltage. If scan tool voltage reading is 351-551 millivolts, go to next step. If scan tool voltage reading is not 351-551 millivolts, go to step 13.
9. Connect a jumper wire between a known-good ground and HO2S harness connector terminal "B" (Purple/White or Purple wire). Using scan tool, monitor HO2S voltage. If voltage reading is 20 millivolts, go to next step. If voltage reading is not 20 millivolts, go to step 14.
10. Remove jumper wire. Using a test light connected to chassis ground, probe HO2S harness connector terminal "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 15.
11. Connect test light between HO2S harness connector terminals "C" (Black wire) and "D" (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 16.
12. Repair cause of HO2S contamination. Replace HO2S sensor. After replacing sensor, go to step 17.
13. Check for short between Tan/White or Tan wire and Purple/White or Purple wire in HO2S circuit. Check for short between Pink wire and Purple/White or Purple wire in HO2S circuit. Repair as necessary. After repairs, go to step 18. If circuits are okay, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
14. Check for open or short in Purple/White or Purple wire, or in Tan/White or Tan wire. Repair as necessary. After repairs, go to step 18.
15. Repair Pink wire between HO2S and underhood fuse block. After repairs, go to step 18.
16. Repair Black wire between HO2S and ground connector terminal. After repairs, go to step 18.
17. Replace HO2S. After replacing sensor, go to next step.
18. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate engine within the Conditions for Running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
19. Using scan tool, reset fuel trim values. Start and operate engine at idle until engine reaches normal operating temperature. Operate engine within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Observe DTC status and verify that DTC runs. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Never solder HO2S wires. Check for improperly installed or defective air intake duct, throttle body and intake manifold leaks, exhaust leaks, HO2S contamination, leaking vacuum hoses or contaminated fuel. An intermittent may be caused by poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1134 OR P1154: HEATED OXYGEN SENSOR TRANSITION TIME RATIO NOT WITHIN CALIBRATED RANGE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is designed to create a voltage relative to oxygen content in engine exhaust stream. The control module supplies HO2S with signal high and low circuits. Ignition voltage and ground are supplied to HO2S heater by independent circuits. The oxygen content of exhaust indicates when engine is operating lean or rich. When HO2S detects that engine is operating rich, the signal voltage is high, and decreases the signal voltage as engine runs leaner. This oscillation is sometimes referred to as activity or switching, can be monitored with HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. HO2S needs to be at a high temperature in order to produce a voltage. When HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors HO2S signal voltage for closed-loop fuel control. During normal closed-loop control operation, control module will add fuel or enrich the mixture, when HO2S detects a lean exhaust content. The control module will subtract fuel or lean out the mixture, when HO2S detects a rich exhaust condition.

This DTC determines if the difference in transition times from lean-to-rich or rich-to-lean has exceeded a maximum ratio. PCM monitors the time needed for HO2S to transition from greater than 600 millivolts to less than 300 millivolts and vice versa. If either of these times are longer than the other by a calibrated ratio, this DTC is set.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404 or P1441 is not set
2. Engine coolant temperature is greater than 135°F (57°C).
3. Engine run time is more than 160 seconds.
4. Mass airflow sensor is 15-55 grams/second.
5. Engine speed is 1100-3000 RPM.
6. The throttle position is greater than 5 percent.
7. System operating in closed-loop.
8. Ignition 1 signal voltage is 9-18 volts.
9. Fuel tank level remaining is greater than 10 percent.
10. Intrusive tests are not in progress
11. Scan tool output controls are not active.
12. Conditions are met for 100 seconds.

Conditions for setting DTC

1. HO2S transition time ratio is not within a calibrated range.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, check for DTCs. If any other DTCs are set, except P1134 or P1154, diagnose affected DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). Operate engine at idle and warm to normal operating temperature. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). Monitor DTC information on scan tool. If DTC P1134 or P1154 fails this ignition cycle, go to next step. If DTC P1134 or P1154 does not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
3. If both DTC P1134 and P1154 fails this ignition cycle, go to step 8. If DTC P1134 and P1154 does not fail this ignition cycle, go to next step.
4. Turn ignition off. Check for an exhaust system leak. Repair exhaust leak as necessary. After repairs, go to step 14. If no exhaust leak is found, go to next step.
5. Ensure that HO2S is securely installed. Check for corrosion on terminals and for proper terminal tension at HO2S and PCM. Check for damaged wiring. Repair as necessary. After repairs, go to step 14. If no problem is found, go to next step.
6. Disconnect HO2S harness connector. Connect a jumper wire between a known-good aground and HO2S harness connector terminal "A" (Tan/White wire or Tan wire). (Scheme 6)or see scheme 7. Turn ignition on, with engine off. Using scan tool in Engine 1 Data List, monitor HO2S voltage. If voltage reading is within 350-550 millivolts, go to next step. If voltage reading is not within 350-550 millivolts, go to step 10.
7. Using jumper wires connected to battery ground, connect one jumper wire to HO2S harness connector "A" (Tan/White or Tan wire) and one jumper wire to HO2S harness connector terminal "B" (Purple/White or Purple wire). Using scan tool, monitor HO2S voltage. If voltage reading is less than 200 millivolts, go to step 13. If voltage reading is not less than 200 millivolts, go to step 9.
8. Turn ignition off. Determine and correct the cause of HO2S contamination before replacing sensor. Check for fuel contamination, improper use of RTV sealant, excessive oil or coolant consumption. Replace affected HO2S. After replacing sensor, go to step 14.
9. Remove jumper wire from HO2S harness connector terminal "A". Check voltage between battery ground and HO2S harness connector terminal "A". If voltage reading is about 5 volts, go to step 12. If voltage reading is not about 5 volts, go to step 11.
10. Turn ignition off. Repair short to ground or short to voltage In Purple/White or Purple wire between HO2S and PCM. After repairs, go to step 14.
11. Turn ignition off. Repair open in Tan/White or Tan wire between HO2S and PCM. If circuit is okay, repair faulty PCM connections. After repairs, go to step 14.
12. Turn ignition off. Repair open in Purple/White or Purple wire between HO2S and PCM. If circuit is okay, repair faulty PCM connections. After repairs, go to step 14.
13. Turn ignition off. Replace appropriate HO2S. After replacing sensor, go to next step.
14. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
15. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Never solder HO2S wires. An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside the insulation.

DTC P1258: ENGINE OVERTEMPERATURE CONDITION

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM uses the Engine Coolant Temperature (ECT) sensor to monitor engine for an over temperature condition. This condition occurs when coolant temperature is greater than 270°F (132°C). When an over temperature condition is present, DTC will set. PCM will alternately disable 4 injectors. By alternately disabling 4 injectors, the PCM is able to reduce coolant temperature.

Conditions for running DTC

1. DTCs P0117, P0118, P1114 and P1115 are not active.
2. Engine is running.

Conditions for setting DTC

1. Engine coolant temperature is greater 270°F (132°C) for more than 10 seconds.

1. Diagnose engine cooling system. After diagnosing engine cooling system, go to next step.
2. Check engine cooling fan for proper operation. If engine cooling fan operates properly, diagnose cause of engine overheating. Check for cooling system or engine mechanical condition. If engine cooling fan does not operate properly, refer to appropriate article in ENGINE COOLING.

DTC P1336: CRANKSHAFT POSITION SENSOR SYSTEM VARIATION NOT LEARNED

Note. For circuit reference, see WIRING DIAGRAMS article.

The Crankshaft Position (CKP) sensor sends pulses to PCM as the reluctor teeth rotate past the CKP sensor. PCM uses the CKP pulses to synchronize ignition and fuel injector operation, and to time interval between each CKP pulse. PCM determines when an excessive change in crankshaft speed occurs by comparing each new time interval with previous interval.

A misfire causes an unexpected change in crankshaft speed. A certain amount of acceleration/deceleration is expected between each firing stroke, but if crankshaft speed changes more than expected amount, PCM interprets this as a misfire. Interval between CKP sensor pulses is extremely small. At high engine speeds, slight variations in the crankshaft, reluctor and CKP sensor components make misfire detection difficult.

PCM learns variations during CKP system variation learning procedure. PCM compensates for these variations when performing detect misfire calculations. Only a scan tool can command PCM to perform CKP system variation learning procedure again. Perform learning procedure after PCM replacement, any operation or repair involving crankshaft, CKP sensor or CKP sensor-to-reluctor wheel gap relationship, engine replacement or when ignition switch was left in on position until battery drained.

Note. Removing power to PCM with ignition on may clear/erase stored pulse value and set this DTC.

Reprogramming PCM does not require running the CKP system variation learn procedure unless PCM is new or from another vehicle. DTC will set when PCM has not learned the crankshaft position system variation.

Conditions for running DTC

1. DTCs P0335, P0336, P0341 or P1345 is not set.

Conditions for setting DTC

1. PCM has not learned the crankshaft position system variation.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Perform CKP Variation Learning procedure as follows: Install scan tool. Apply parking brakes and block drive wheels. Close hood. Place transmission in Park (A/T) or Neutral (M/T). Warm engine to 150°F (65°C). Turn off all accessories. Apply service brakes for duration of procedure. Enable CKP SYSTEM VARIATION LEARN PROC. on scan tool. Slowly increase engine speed to 4000 RPM. Immediately release throttle when engine speed decreases. If scan tool shows CKP learn procedure is complete, go to step 5 . If scan tool does not show CKP learn procedure is complete, go to next step.
3. Attempt CKP learn procedure as many as 3 times. If scan tool indicates that learn procedure is complete, go to step 5 . If scan tool does not indicate that learn procedure is complete, go to next step.
4. Check CKP sensor and crankshaft reluctor wheel for damage. If problem is found, go to step 6 . If no problem is found, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Turn ignition off for 15 seconds, then go to step 7 .
6. Replace CKP sensor and/or reluctor wheel. After replacing CKP sensor, perform CKP System Variation Learn Procedures. See step 2 . After performing learn procedures, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within the conditions for setting this DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2 .
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.

If CKP learn procedure cannot be learned, check for a chipped or damaged reluctor wheel, incorrect CKP sensor alignment to reluctor wheel, excessive crankshaft runout, interference in signal circuit to CKP sensor or incorrect ratio of crankshaft to camshaft pulses.

If PCM receives an incorrect crankshaft to camshaft ratio, PCM will not allow scan tool to enable the learn procedure.

DTC P1345: CRANKSHAFT/CAMSHAFT POSITION SENSOR CORRELATION

Note. For circuit reference, see WIRING DIAGRAMS article.

This DTC monitors the Crankshaft Position (CKP) and Camshaft Position (CMP) signals to determine if they are synchronized. If both signals are not observed by the PCM within a specified time, PCM will determine that error has occurred. DTC will set when engine is running, cam sensor reference pulse is not detected at correct relative position with crank pulse.

DTC will run when engine is running and DTC will set when engine is running and cam sensor pulse is not detected at the correct relative position to CKP sensor pulse.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Start engine. Using scan tool, monitor engine RPM. If engine RPM fluctuates up to twice the expected RPM, go to next step. If engine RPM does not fluctuate up to twice the expected RPM, go to step 4 .
3. Turn ignition off. Replace CKP sensor. After replacing sensor, go to step 9 .
4. Raise engine speed to 1000 RPM. Monitor camshaft retard on scan tool. If camshaft retard is -5 to -17 degrees, go to next step. If camshaft retard is not -5 to -17 degrees, go to step 6 .
5. Raise engine speed to 2000 RPM. Check camshaft retard on scan tool. If camshaft retard changes more than 2 degrees of previous reading, go to next step. If camshaft retard does not change more than 2 degrees of previous reading, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
6. Turn ignition off. Check for proper installation of distributor. Remove distributor cap and gently attempt to rotate rotor. If rotor turns on distributor shaft, go to step 8 . If rotor does not turn on distributor shaft, go to next step.
7. Check distributor for proper installation. Repair as necessary. After repairs, go to step 9 . If distributor installation is okay, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
8. Replace distributor. After replacing distributor, go to next step.
9. Turn ignition on, with engine off. Using the scan tool, clear the DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running this DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
10. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Check for loose CMP sensor, excessive free play in timing chain and gear assembly, incorrectly installed distributor, loose rotor or distributor hold-down bolt. An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1380: MISFIRE DETECTED - ROUGH ROAD DATA NOT AVAILABLE

Note. For circuit reference, see WIRING DIAGRAMS article.

This test determines if EBCM has lost the ability to provide rough road data to PCM for misfire detection (DTC P0300). DTC will set when PCM determines that ABS system is unable to detect a rough road condition.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0121, P0122, P0123, P0335, P0336 or P0742 is not set
2. Vehicle speed is greater than 10 MPH.
3. Engine load is less than 60 percent.
4. Engine misfire is detected and DTC P0300 set.
5. Engine speed is less than 3200 RPM.

Conditions for setting DTC

1. ABS malfunction exists preventing the PCM from receiving rough road detection data.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Perform ABS system diagnosis. See appropriate ANTI-LOCK article in BRAKES. Repair as necessary.

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

DTC P1381: SERIAL DATA MALFUNCTION EXISTS - PREVENTING PCM FROM RECEIVING ROUGH ROAD DETECTION DATA

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. For accurate detection of engine misfire, PCM must distinguish between crankshaft deceleration caused by actual misfire and deceleration caused by rough road conditions. The ABS can detect if vehicle is on a rough road based on wheel acceleration or deceleration data supplied by the wheel speed sensors. If ABS detects rough road greater than a predetermined threshold, this information is sent to PCM via serial data. PCM can then take the rough road into account when calculating misfire. If ABS is malfunctioning and cannot detect rough roads, the misfire diagnostic will continue to run. However, if a misfire DTC sets, this additional DTC also sets indicating that rough road data was not available during the misfire calculation due to a serial data malfunction.

Conditions for running DTC

1. Vehicle speed is greater than 10 MPH.
2. Engine speed is less than 3200 RPM.
3. Engine load is less than 60 percent.
4. Engine misfire is detected and DTC P0300 is set.

Conditions for setting DTC

1. A serial data malfunction exists preventing the PCM from receiving rough road detection data.
2. Conditions are met for 20 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Perform ABS system diagnosis. See appropriate ANTI-LOCK article in BRAKES. Repair as necessary

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.

DTC P1404: EGR VALVE IS STILL OPEN WHEN PCM IS COMMANDING EGR VALVE CLOSED

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM monitors the EGR valve pintle position input in order to ensure that EGR valve responds properly to the commands from PCM. When ignition is on, PCM learns the EGR learned minimum position. The PCM compares EGR learned minimum position to EGR position sensor when the EGR valve is commanded closed. If EGR position sensor indicates that EGR valve is still open when PCM is commanding EGR valve closed, this DTC will set.

Conditions for running DTC

1. Ignition voltage is greater than 11.7 volts.
2. PCM has enabled the EGR valve.

Conditions for setting DTC

1. EGR position sensor is 0.29 volt greater than the EGR learned minimum position when the desired EGR position is commanded to zero percent.
2. Vehicle must be driven.
3. Condition must be present 3 times.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Using scan tool, command EGR valve from zero percent to 100 percent. If EGR position sensor remains close to desired EGR position at all commanded positions, go to next step. If EGR position sensor does not remain close to desired EGR position at all commanded positions, go to step 4.
3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC or as close as possible to the FREEZE FRAME/FAILURE RECORDS data. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC dos not fail this ignition cycle, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l).
4. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on, with engine off. Using a test light connected to ground, probe EGR valve harness connector terminal "E" (Red wire). (Scheme 5) Using scan tool, command EGR valve between zero and 10 percent. If test light turns on and off with each command, go to next step. If test light does not turn on and off with each command, go to step 13.
5. Using scan tool, observe EGR position sensor parameter. If EGR position sensor is at zero percent, go to next step. If EGR position sensor is not at zero percent, go to step 9.
6. Check voltage between EGR valve harness connector terminal "B" (Black wire) and "D" (Gray wire). If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 8.
7. Connect a fused jumper wire between EGR valve harness connector terminals "C" (Brown wire) and "D" (Gray wire). If scan tool indicates that EGR position sensor value is about 100 percent, go to step 14. If scan tool does not indicate that EGR position sensor value is not about 100 percent, go to step 11.
8. Check voltage between a known-good ground and EGR valve harness connector terminal "D" (Gray wire). If voltage reading is about 5 volts, go to step 10. If voltage reading is not about 5 volts, go to step 12.
9. Turn ignition off. Check for short to voltage in Brown wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 15.
10. Turn ignition off. Check for open or high resistance in Black wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 15.
11. Turn ignition off. Check for high resistance or short to ground in Brown wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 15.
12. Turn ignition off. Check for open, short to ground, or short to voltage in Gray wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 15.
13. Turn ignition off. Check for short to voltage in Red wire between EGR valve and PCM. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 15.
14. Turn ignition off. Check for poor connections EGR valve harness connector. Repair as necessary. After repairs, go to step 18. If connections are okay, go to step 16.
15. Check for poor connections PCM harness connector. Repair as necessary. After repairs, go to step 18. If connections are okay, go to step 17.
16. Replace EGR valve. After replacing EGR valve, go to step 18.
17. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
18. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
19. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

Check for excessive deposits on EGR valve pintle or seat. Remove EGR valve and check for deposits that can interfere with EGR valve pintle extending completely or deposits that can cause pintle to stick.

The AIR pump is used to lower tailpipe emissions on start-up. PCM supplies ground to AIR pump relay to energize the AIR solenoid and pump. PCM will run a test using HO2S voltages to diagnose AIR system. During this test, PCM will activate AIR pump during closed-loop operation. When system is activated, PCM will monitor HO2S voltages and short term fuel trim values for both engine banks. If AIR system is operating properly, HO2S voltages should go low and short term fuel trim should go high.

PCM checks HO2S voltages return to greater than a rich threshold when AIR pump is disabled. If PCM determines that HO2S voltages for both banks did not respond as expected during the tests, DTC P0410 will set. If only one sensor responded, PCM will set either DTC P1415 or P1416 to indicate which bank the AIR system is inoperative.

Conditions for running DTC

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0300, P0440, P0442, P0446, P0506 or P0507 is not set
2. Engine run time is more than 15 seconds after closed-loop operation.
3. Engine load is less than 33 percent.
4. Engine airflow is less than 20 grams/second.
5. Engine speed is greater than 750 RPM.
6. Ignition voltage is greater than 11.7 volts.
7. Air/fuel ratio is 14.7:1.
8. Engine coolant temperature is 35-230°F (2-110°C).
9. Intake air temperature is 14-212°F (-10 to 100°C).
10. Fuel system is not operating in power enrichment or deceleration fuel cut-off.
11. Start-up engine coolant temperature is less than 176°F (80°C).
12. Vehicle speed is greater than 25 MPH.

Conditions for setting DTC

1. HO2S voltage does not go less than 222 millivolts for 1.2 seconds or more.
2. Short term fuel trim does not go greater than a predetermined amount.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Operate engine at idle. Ensure engine in closed-loop. Turn all accessories off. Using scan tool, monitor HO2S-1 voltage display. Enable AIR pump using scan tool. Observe and record HO2S voltage as AIR pump is enabled. If HO2S voltage drops to less than 350 millivolts, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If HO2S voltage does not drop to less than 350 millivolts, go to next step.
3. Turn ignition off. Inspect all hoses and pipes for proper connection. Ensure clamps are secure on pipes and hoses. Check for kinks, holes or pinched hoses and pipes. Check components with evidence of heat damage. Repair as necessary. After repairs, go to step 6 . If no problem is found, go to next step.
4. Disconnect hose from the applicable check valve at exhaust manifold. Using scan tool, enable AIR pump. If air is present at hose outlet, go to step 7 . If air is not present at hose outlet, go to next step.
5. Repair restriction or blockage in applicable bank AIR hoses and pipes between exhaust manifold and the point where system branches to both sides of engine. After repairs, go to step 8 .
6. Repair condition found. After repairs, go to step 8 .
7. Replace appropriate check valve. After replacing check valve, go to next step.
8. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) . If DTC runs and passes, go to next step. If DTC resets, go to step 2 .
9. Using scan tool review the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Remove any debris from PCM connector surfaces before servicing PCM. Inspect PCM connector gaskets when diagnosing or replacing PCM. Ensure that the gaskets are installed correctly to prevent water intrusion into PCM. Casting flash in exhaust manifold may restrict amount of airflow necessary to affect HO2S voltage. Remove air pipe from manifold and inspect passage.

Using the FREEZE FRAME/FAILURE RECORDS may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the FREEZE FRAME/FAILURE RECORDS data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same FREEZE FRAME conditions observed in order to isolate when DTC failed. Duplicate conditions such as RPM, load, vehicle speed and temperature will also cause DTC to set.

DTC P1441: EVAPORATIVE SYSTEM - VACUUM IS GREATER THAN CALIBRATED VALUE ("L" & "M" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

Evaporative (EVAP) emissions canister purge is controlled by a solenoid valve which allows ported vacuum to purge canister when energized by PCM. A vacuum switch in purge line is used to detect when system is being purged. PCM supplies and reads a 12-volt reference to switch. DTC will set when EVAP system develops a vacuum greater than a calibrated value when purge is not commanded.

Conditions for running DTC

1. DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1112, P1114, P1115 or P1122 is not set
2. Ignition voltage is 10-18 volts.
3. Barometric pressure is greater than 75 kPa.
4. Fuel level is 15-85 percent.
5. Engine coolant temperature and intake air temperature is 39-86°F (4-30°C).
6. Start up engine coolant temperature and intake air temperature are within 16°F (9°C) of each other.
7. VSS is less than 75 MPH.

Conditions for setting DTC

1. PCM detects vacuum during a non-purge condition.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, retrieve DTCs. If DTCs P0443, P0449, P0452 or P0453 is also set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If DTCs P0443, P0449, P0452 or P0453 is not set, go to next step.
3. Remove fuel fill cap. Using scan tool, monitor Fuel Tank Pressure (FTP). If scan tool indicates that FTP is within -0.5 to 0.5 in. H2O, go to next step. If scan tool does not indicate that FTP is within -0.5 to 0.5 in. H2O, go to «DTC P0453»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0453-fuel-tank-pressure-sensor) .
4. Disconnect EVAP canister purge pipe from EVAP canister purge solenoid. Install a hand-held vacuum gauge to EVAP canister purge port. Disconnect EVAP canister purge solenoid harness connector. Monitor vacuum on vacuum gauge. Start and operate engine at idle. Increase idle to 1200-1500 RPM. If vacuum increases, go to next step. If vacuum does not increase, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
5. Replace EVAP canister purge solenoid. After replacing solenoid, go to next step.
6. Using scan tool, review and record the FREEZE FRAME/FAILURE RECORDS data. Using scan tool, clear DTCs and perform Service Bay Test. If scan tool indicates that service bay test passed, go to next step. If scan tool does not indicate that service bay test passed, go to step 3 .
7. Using a scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

An intermittent condition could be caused by an improperly installed or damaged EVAP canister purge solenoid or a temporary blockage in the EVAP canister purge solenoid. Repair blockage in EVAP system.

DTC P1441: EVAPORATIVE SYSTEM - VACUUM IS GREATER THAN CALIBRATED VALUE ("S" & "T" SERIES)

Note. For circuit reference, see WIRING DIAGRAMS article.

PCM monitors the amount of vacuum pressure in the Evaporative Emissions (EVAP) system by monitoring the Fuel Tank Pressure (FTP) sensor signal. PCM seals the EVAP system by commanding EVAP canister purge solenoid off and EVAP canister vent solenoid on. PCM monitors the FTP sensor in order to determine if EVAP canister purge solenoid is leaking vacuum to EVAP system. This DTC sets if vacuum in EVAP system is greater than a predetermined value within a predetermined time.

Conditions for running DTC

1. DTCs P0107, P0108, P0112, P0113, P0121, P0122, P0123, P0131-P0161, P0420, P0430, P0500, P0502, P0503, P0562, P0563, P1111, P1112, P1114 or P1115 is not set.
2. No active HO2S, IAT, MAP, TP or VSS DTCs.
3. No active system voltage DTCs.
4. Ignition voltage is 10-18 volts.
5. Barometric pressure is greater than 75 kPa.
6. Fuel level is 15-85 percent.
7. Engine coolant temperature and intake air temperature is 39-86°F (4-30°C).
8. Start up engine coolant temperature and intake air temperature are within 14°F (8°C) of each other.
9. Throttle position angle is 0-99.6 percent.

Conditions for setting DTC

1. EVAP system develops a vacuum more than a predetermined value when purge is not commanded.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check) . After performing powertrain diagnostic system check, go to next step.
2. Using scan tool, retrieve DTCs. If DTCs P0443, P0449, P0452 or P0453 is also set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If DTCs P0443, P0449, P0452 or P0453 is not set, go to next step.
3. Using scan tool, monitor FTP sensor. If scan tool indicates that fuel tank pressure is within -0.5 to 0.5 in. H2O, go to step 5 . If scan tool does not indicate that fuel tank pressure is within -0.5 to 0.5 in. H2O, go to next step.
4. Disconnect FTP sensor harness connector (sensor located on top of fuel tank). Using scan tool, monitor FTP sensor. If scan tool indicates fuel tank pressure is within -0.5 to 0.5 in. H2O, go to step 6 . If scan tool does not indicate that fuel tank pressure is within -0.5 to 0.5 in. H2O, go to «DTC P0453»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__dtc-p0453-fuel-tank-pressure-sensor) .
5. Turn ignition off. Disconnect purge pipe from EVAP canister purge solenoid. Install a vacuum gauge to EVAP canister purge port. Disconnect EVAP canister purge solenoid harness connector. Monitor vacuum on vacuum gauge. Start and operate engine at idle. Increase idle to 1200-1500 RPM. If vacuum increases, go to step 7 . If vacuum does not increase, see «DIAGNOSTIC AIDS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) .
6. Turn ignition off. Replace FTP sensor. After replacing sensor, go to step 8 .
7. Turn ignition off. Replace EVAP canister purge solenoid. After replacing canister purge solenoid, go to next step.
8. Turn ignition on, with engine off. Using scan tool, review and record the FREEZE FRAME/FAILURE RECORDS data. Using scan tool, clear DTCs and perform Service Bay Test. If scan tool indicates that service bay test passed, go to next step. If scan tool does not indicate that service bay test passed, go to step 3 .
9. Using scan tool, select the Review Info option. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) . If no DTCs are displayed, system is okay.

Remove any debris from PCM connector surfaces before servicing PCM. Inspect PCM connector gaskets when diagnosing/replacing PCM. Ensure that gaskets are installed correctly to prevent water intrusion into PCM.

An intermittent condition could be caused by an improperly installed or damaged EVAP canister purge solenoid or a temporary blockage in EVAP canister purge solenoid. Repair blockage in EVAP system.

DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT OUT OF TOLERANCE

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM uses the 5-volt reference 1 circuit as a sensor feed to the TP sensor and MAP sensor. PCM monitors voltage on the 5-volt reference 1 circuit. If voltage is out of range/tolerance, DTC will set.

DTC will run when engine is running and DTC will set when PCM detects a voltage out of range/tolerance condition on the 5-volt reference 1 circuit for more than 10 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
3. Check PCM and engine grounds. Ensure that grounds are clean and secure. Repair as necessary. After repairs, go to step 12. If no problem is found, go to next step.
4. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on, with engine off. Using a DVOM, check voltage between engine ground and TP sensor harness connector terminal "A" (Black wire on "L" and "M" Series or Gray wire on "S" and "T" Series). (Scheme 4) If voltage reading is about 5 volts, go to step 6. If voltage reading is not about 5 volts, go to next step.
5. If voltage reading is greater than 5 volts, go to step 9. If voltage reading is not greater than 5 volts, go to step 7.
6. Reconnect TP sensor harness connector. Disconnect MAP sensor harness connector. Using DVOM, check voltage between engine ground and MAP sensor harness connector terminal "C" (Gray wire). (Scheme 3) If voltage reading is about 5 volts, problem is intermittent. If voltage reading is not about 5 volts, go to step 10.
7. Monitor DVOM while disconnecting all other devices connected to 5-volt reference circuit one at a time. See WIRING DIAGRAMS. If voltage changes when one of the components are disconnected, replace the component. After replacing component, go to step 12. If no problem is found, go to next step.
8. Disconnect PCM harness connector. Check the 5-volt reference circuit for a short to ground or any sensor low reference circuit. If a problem is found, repair as necessary. After repairs, go to step 12. If no problem is found, go to step 11.
9. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Check for short to voltage Gray wire between MAP sensor and PCM or shorted to Black wire in MAP sensor circuit. Repair as necessary. After repairs, go to step 12. If circuits are okay, go to step 11.
10. Replace TP sensor. After replacing sensor, go to step 12.
11. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
12. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC runs and passes, go to next step. If DTC resets, go to step 2.
13. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

DTC P1639: 5-VOLT REFERENCE 2 CIRCUIT OUT OF TOLERANCE

Note. For circuit reference, see WIRING DIAGRAMS article.

The PCM uses the 5-volt reference 2 circuit as a sensor feed for the Fuel Tank Pressure (FTP) sensor. The PCM monitors the voltage on the 5-volt reference 2 circuit. If voltage is out of range/tolerance, DTC will set.

DTC will run when engine is running and DTC will set when PCM detects a voltage out of range/tolerance condition on the 5-volt reference 2 circuit for more than 10 seconds.

1. Perform powertrain diagnostic system check. See «POWERTRAIN DIAGNOSTIC SYSTEM CHECK»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-diagnostic-system-check). After performing powertrain diagnostic system check, go to next step.
2. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, problem is intermittent.
3. Check PCM and engine grounds. Ensure grounds are clean and secure. Repair as necessary. After repairs, go to step 13. If no problem is found, go to next step.
4. Turn ignition off. Disconnect FTP sensor harness connector (sensor is located on top of fuel tank). Connect a DVOM between a known-good ground and FTP sensor harness connector terminal "B" (Dark Green wire). (Scheme 7) Turn ignition on, with engine off. If voltage reading is about zero volts, go to next step. If voltage reading is not about zero volts, go to step 7.
5. Turn ignition off. Connect a DVOM between a known-good ground and FTP sensor harness connector terminal "C" (Gray wire). Turn ignition on, with engine off. If voltage reading is about 5 volts, go to step 11. If voltage reading is not about 5 volts, go to next step.
6. If voltage reading is greater than 5 volts, go to next step. If voltage reading is not greater than 5 volts, go to step 8.
7. Disconnect PCM harness connector. Check for short to voltage on Gray wire or Dark Green wire between FTP sensor and PCM. Repair as necessary. After repairs, go to step 13. If circuits are okay, go to step 12.
8. Turn ignition off. Using DVOM, check for continuity of Gray wire and Dark Green wire. If continuity does not exist, go to next step. If continuity exists, go to step 10.
9. Leave ignition off. Using DVOM, check for continuity between Gray wire and a known-good ground. If continuity does not exist, go to step 12. If continuity exists, go to next step.
10. Repair for short to chassis ground or short to FTP sensor ground circuit (Black wire). After repairs, go to step 13.
11. Turn ignition off. Replace FTP sensor. After replacing sensor, go to step 13.
12. Replace PCM. Perform PCM relearn procedure. See «POWERTRAIN CONTROL MODULE»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING. After replacing PCM, go to next step.
13. Using scan tool, select DTC option and Clear DTC. Operate engine at idle and warm engine to normal operating temperature. Select DTC option and Specific DTC option, then enter this DTC on scan tool. Operate vehicle within the conditions for running the DTC. See «CODE ENABLE CRITERIA»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l). If scan tool indicates that this test ran and passed, go to next step. If DTC resets, go to step 2.
14. Using scan tool, select the Capture Info option and Review Info option. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions). If no DTCs are displayed, system is okay.

See also:
• MODEL IDENTIFICATION
• DIAGNOSTIC PROCEDURE
• POWERTRAIN DIAGNOSTIC SYSTEM CHECK
• DIAGNOSTIC TROUBLE CODE DEFINITIONS
• CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE
• ENABLE CRITERIA
• ENABLING CRITERIA
• P0101
• P0102
• P0103
• P0106
• P0107
• P0108
• P0112
• P0113
• P0117
• P0118
• P0121
• P0122
• P0123
• P0125
• P0128
• P0131 OR P0151
• P0132 OR P0152
• P0133 OR P0153
• P0134 OR P0154
• P0135
• P0137
• P0138
• P0140
• P0141
• P0155
• P0171 OR P0174
• P0172 OR P0175
• P0200
• P0230
• P0300
• P0325
• P0327
• P0335
• P0336
• P0341
• P0351
• P0401
• P0404
• P0405
• P0410
• P0418
• P0420 OR P0430
• P0440
• P0442
• P0443
• P0446
• P0449
• P0452
• P0453
• P0500
• P0506
• P0507
• P0601-P0607, P1600, P1621, P1627, P1680, P1681 OR P1683
• P0650
• P0719
• P0724
• P1111
• P1112
• P1114
• P1115
• P1121
• P1122
• P1133 OR P1153
• P1134 OR P1154
• P1258
• P1336
• P1345
• P1380
• P1381
• P1404
• P1441
• P1635
• P1639
• CODE TYPES
• POWERTRAIN CONTROL MODULE
• CODE ENABLE CRITERIA