Engine Control System - Self-Diagnostics - 4.2L: Diagnosis Chevrolet TrailBlazer I

ON-BOARD DIAGNOSTICS

The Powertrain Control Module (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, in most cases, illuminate the Malfunction Indicator Light (MIL) located on instrument cluster.

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

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

DIAGNOSTIC STARTING POINT - ENGINE CONTROLS

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 «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) .
2. If no DTCs are present and a driveability problem exists, see «SYMPTOMS»(ref-152936-S08695756652003030500000) in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Doing so will help identify proper system or component to check in «SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-153168) article.
3. After necessary repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation and ensure DTC does not reset.

Diagnostic Procedures

Note. Do not perform this diagnostic procedure if there is not a driveability concern, unless another procedure directs you to this diagnostic. Before you proceed with diagnosis, search for applicable service bulletins. Unless a diagnostic procedure instructs you, DO NOT clear the DTCs. If there is a condition with the starting system, see appropriate STARTERS article in ELECTRICAL. Ensure the battery has a full charge. Ensure the battery cables are clean and tight. Ensure the PCM grounds are clean, tight, and in the correct location.

1. Install scan tool. Does scan tool turn ON? If yes, go to next step. If no, see SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
2. Turn ignition on, with engine off. Attempt to establish communication with the listed control modules. If you are using a Tech 2, obtain the information using the Class 2 Message Monitor feature: PCM. Vehicle Theft Deterrent (VTD). Instrument Panel (IP) cluster. Electronic Brake Control Module (EBCM). Heating, Ventilation, and Air Conditioning (HVAC). Does scan tool communicate with all the listed control modules? If yes, go to next step. If no, see SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
3. Attempt to start the engine. Does the engine start and idle? If yes, go to next step. If no, see «HARD START»(ref-152936-S39840238642003030500000) in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Select the DTC display function for the following control modules: PCM, VTD, IP Cluster, EBCM, HVAC. Does scan tool display any DTCs? If yes, go to next step. If no, go to step 9 .
5. With scan tool, select Captured Info in order to store the powertrain DTC information. Go to next step.
6. Does scan tool display DTCs which begin with a "U"? If yes, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If no, go to next step.
7. Does scan tool display DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681 or P1683? If yes, see «DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683 OR P2610: PCM MEMORY»(ref-155898-S33851621052003062800000) under DIAGNOSTIC TESTS. If no, go to next step.
8. Does scan tool display DTC P0562, P0563, P1621 or P1622? If yes, see appropriate GENERATORS & REGULATORS article in ELECTRICAL. If no, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) .
9. Is the customer's concern with the automatic transmission? If yes, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If no, go to next step.
10. Is the customer's concern with the Inspection and Maintenance (I/M) testing? If yes, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155898-S37237432342003062800000) under DRIVE CYCLES. If no, go to next step.
11. Review the following symptoms. Hard start, surges/chuggles, lack of power, sluggishness, sponginess, detonation/spark knock, hesitation, sag, stumble, cuts out, misses, poor fuel economy, poor fuel fill quality, rough, unstable, or incorrect idle and stalling, dieseling, run-on and backfire. See «SYMPTOMS»(ref-152936-S08695756652003030500000) in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Did you find and correct the condition? If yes, system is okay. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

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 DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS. (Scheme 49) DLC is located below left side of dash.

Scheme 49

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.

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. About 80 percent of driveability problems occur without setting DTCs. Sensors that are out of calibration will not set a DTC but will cause driveability problems.

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

Note. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent DTCs 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 the use of a 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 over 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.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM. Repair any DTCs or driveability concerns that would prevent the I/M System Status tests from completing. Did you find and repair a DTC or driveability concern? If yes, go to step 3 . If no, go to next step.
2. Review any service bulletins for software updates that may prevent I/M readiness. Perform any reprogramming or repairs indicated by the service bulletins. Was a reprogramming or repair service required? If yes, see «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(ref-155898-S22460740922003062800000) . If no, go to next step.
3. With scan tool, observe the I/M System Status display. Is more than one test indicating a NO status? If yes, see «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(ref-155898-S22460740922003062800000) . If no, go to the I/M System Set Procedure for the indicated system.

Diagnostic Aids

The I/M System Status display provides an indication of when the control module has completed the required tests. This does not necessarily mean that the test has passed, only that a decision was made. If the diagnostic fails, a DTC will indicate the failure. If a failure indication is present for a DTC associated with one of the I/M regulated systems, the failure indication may prevent other required tests from running. For example, a DTC for the control circuit of the relay controlling an AIR pump may not be listed in the INSPECTION/MAINTENANCE SYSTEM DTCS table because this is a continuous test. If this DTC is set, the Active Tests for the AIR system may not run. The I/M System Status information may be useful for a technician to determine if diagnostics have run when verifying repairs.

Conditions For Running

Cold Start

1. Barometric (BARO) pressure is more than 22 in. Hg (74 kPa).
2. Engine Coolant Temperature (ECT) is less than 86°F (30°C).
3. Intake Air Temperature (IAT) is less than 86°F (30°C).
4. The difference between the Intake Air Temperature (IAT) and the Engine Coolant Temperature (ECT) is 14°F (8°C) or less.
5. Battery voltage is 9-18 volts.
6. Fuel level is 1/4 and 3/4.

1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155898-S37237432342003062800000) .
2. Preprogram scan tool with the vehicle information before the ignition is turned ON. Ensure that the vehicle is within the CONDITIONS FOR RUNNING DTC. Turn OFF all of the accessories, e.g., A/C, blower fan, etc. Set the vehicle parking brake. Verify that the transmission is in Park for automatic transmissions and Neutral for manual transmissions. Start the engine and allow the engine to idle. Allow the engine to idle for 2 minutes. When complete, go to next step.
3. In order for the next group of tests to run, the vehicle must operate in the following conditions: Acceleration at part throttle to 55 MPH with this speed maintained until the engine reaches operating temperature. This may be up to 8-10 minutes depending on the start up coolant temperature. Continued operation under these conditions for an additional 6 minutes. When complete, go to next step.
4. In order for the next group of tests to run, the vehicle must operate in the following conditions: Vehicle speed reduced to 45 MPH with this speed maintained for one additional minute. Four decelerations of 25 seconds each from 45 MPH while the following criteria is maintained: The throttle is closed. NO brake application on either manual or automatic transmission. NO clutch actuation on a manual transmission. NO manual downshift. The vehicle speed remains more than 25 MPH. After each deceleration period, the vehicle is returned to 45 MPH under part throttle acceleration and the speed is maintained for 15 seconds. When complete, go to next step.
5. In order for the next group of tests to run, the vehicle must operate in the following conditions: Acceleration at part throttle to 45-55 MPH with this speed maintained for 2 minutes. Deceleration to zero MPH. Engine idling for 2 minutes while the following criteria is maintained: Service brake depressed. Automatic transmission in drive. Manual transmission in neutral with the clutch pedal depressed. When complete, go to next step.
6. With scan tool, observe the I/M System Status display. Did all of the I/M System Status indicators update to YES? If yes, go to next step. If no, go to the I/M System Set Procedure for the indicated systems.
7. With scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures may prevent tests such as Heated Oxygen Sensor (HO2S) Heater and Evaporative (EVAP) emission System from initiating. If a step is interrupted before completion, perform the remaining portion of the set procedures. Any portion of the set procedure that requires the engine at operating temperature may be repeated. This allows most of the diagnostics to run and the remaining tests can be performed using the individual System Set Procedures. If the vehicle has recently run, start this procedure at step 3 . This will allow the tests that require the engine at operating temperature to run. Using this method allows shorter cool down periods if the tests requiring a cold start do not initiate. The scan tool can be used to monitor each of the I/M System Status indicators during the I/M Complete System Set Procedure. When all of the indicators for a test step have updated to YES, testing can move on to the next step even if the remaining portion of the test is not complete. For example, step 3 is designed to run the EVAP, secondary Air Injection (AIR), and HO2S tests. The procedure instructs the technician to operate the vehicle in the enable conditions for 6 minutes. If all 3 tests have updated to YES within 4 minutes, it is not necessary to continue with the enable conditions and testing can advance to the next step.

INSPECTION/MAINTENANCE SYSTEM DTCS

1. Barometric (BARO) pressure is more than 22 in. Hg (74 kPa).
2. Engine coolant is at operating temperature, 160-248°F (71-120°C).
3. Intake Air Temperature (IAT) is 5-167°F (-15 to 75°C).
4. Engine is in Closed Loop fuel control.
5. Engine has run for 6-8 minutes off idle in order to initiate test.
6. Battery voltage is 11-18 volts.

1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155898-S37237432342003062800000) .
2. Ensure the vehicle is within the «CONDITIONS FOR RUNNING»(ref-155898-S07849106282003062800000) . Turn OFF all of the accessories (e.g., A/C, blower fan, etc.). Start the engine and allow the engine to idle. For this test to run, the vehicle must operate in the following conditions: Acceleration at part throttle to 55 MPH with this speed maintained for 5 minutes. Deceleration to zero MPH. Engine idling for 2 minutes while the following criteria is maintained: Service brake depressed. Automatic transmission in Drive. Manual transmission in Neutral with the clutch pedal depressed. With scan tool, observe the I/M System Status display. Did the Catalyst System Status update to YES? If yes, go to step 5 . If no, go to next step.
3. With scan tool, observe the DTC Information. Does scan tool indicate any failed DTCs? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
4. To determine which DTCs are required to run in order to complete this test, see «INSPECTION/MAINTENANCE SYSTEM DTCS»(ref-155898-S08605071532003062800000) table. With 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 the vehicle within the Conditions For Running DTC, located in appropriate DTC test. Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat steps 4-6 for any additional required DTCs that have not run. With scan tool, observe the I/M System Status display. Did the Catalyst System Status update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S39274004852003062800000) .
5. With scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The control module runs a maximum of 6 tests per trip until the Catalyst System Status updates to YES. If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES. The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the Malfunction Indicator Light (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs). The first failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met 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.

Non Scan Tool Service Bay Test

1. The barometric pressure is more than 22 in. Hg (75 kPa).
2. Fuel level is 1/4 and 3/4.
3. The battery voltage is 10-18 volts.
4. The test will initiate only after a cold start. The control module considers the engine to be cold if the following conditions are met: Engine Coolant Temperature (ECT) is 39-86°F (3.8-30.0°C). Intake Air Temperature (IAT) is 39-86°F (3.8-30.0°C). The difference between the ECT and IAT is less than 14°F (8°C).

Scan Tool Service Bay Test

1. Barometric (BARO) pressure is more than 22 in. Hg (75 kPa).
2. ECT is less than 176°F (80°C).
3. Fuel level is 1/4 and 3/4.
4. Battery voltage is 10-18 volts.

1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155898-S37237432342003062800000) .
2. Using scan tool, select Special Functions. Determine if the vehicle is equipped with a Service Bay Test for the EVAP System. Is the vehicle equipped with EVAP Service Bay Test? If yes, go to next step. If no, go to step 5 .
3. Ensure that the vehicle is within the «CONDITIONS FOR RUNNING»(ref-155898-S11604503962003062800000) . Turn OFF all of the accessories (e.g., A/C, blower fan, etc.). Following the directions on scan tool, perform the EVAP Service Bay Test. Did the EVAP System pass the Service Bay Test? If yes, go to step 8 . If no, go to next step.
4. Observe scan tool Service Bay Test for an indication of why the test did not pass, (e.g., failed DTC, test aborted, etc.). Repair condition as necessary. After repair, see «INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE»(ref-155898-S22460740922003062800000) .
5. Ensure that the vehicle is within the «CONDITIONS FOR RUNNING»(ref-155898-S11604503962003062800000) . Turn OFF all of the accessories (e.g., A/C, blower fan, etc). Start the engine and idle. To run this test, the vehicle must operate in the following conditions: Acceleration at part throttle to 45 MPH with this speed maintained until the engine reaches operating temperature. This may be up to 8-10 minutes depending on the start up coolant temperature. Continue the operating conditions for an additional 3 minutes after the engine reaches operating temperature, or until the I/M System Status indicator updates to YES. Did the EVAP System Status update to YES? If yes, go to step 8 . If no, go to next step.
6. With scan tool, observe the DTC Information. Does scan tool indicate any failed DTCs? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
7. To determine which DTCs are required to run in order to complete this test, see «INSPECTION/MAINTENANCE SYSTEM DTCS»(ref-155898-S08605071532003062800000) table. With 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 the vehicle within the Conditions For Running DTC, located in appropriate DTC test. Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this procedure for any additional required DTCs that have not run. With scan tool, observe the I/M System Status display. Did the EVAP System Status update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S19736575522003062800000) .
8. With scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Extreme high or low ambient temperatures may prevent the EVAP System Tests from initiating. Performing a visual inspection prior to running the 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 the 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 the I/M System Status display will indicate the Malfunction Indicator Light (MIL) is requested. The I/M System Status also registers the number of Diagnostic Trouble Code (DTC). 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.

1. Engine Coolant Temperature (ECT) is more than 135°F (57°C).
2. Engine is running in Closed Loop fuel control.
3. Engine has been running for more than 160 seconds.
4. Battery voltage is 9-18 volts.

1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155898-S37237432342003062800000) .
2. Ensure that the vehicle is within the CONDITIONS FOR RUNNING DTC. Turn OFF all of the accessories (e.g., A/C, blower fan, etc.). Start the engine and allow it to idle. To run this test, the vehicle must operate in the following conditions: Acceleration at part throttle to 45-55 MPH with this speed maintained for 6 minutes or until the I/M System Status updates to YES. On manual transmissions, either 5 or 6-speed, may require operation in 4th or 5th gear respectively in order for this test to run. With scan tool, review the I/M System Status display. Did the HO2S/O2S System Status update to YES? If yes, go to step 5 . If no, go to next step.
3. With scan tool, observe the DTC Information. Does scan tool indicate any failed DTCs? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
4. To determine which DTCs are required to run in order to complete this test, see «INSPECTION/MAINTENANCE SYSTEM DTCS»(ref-155898-S08605071532003062800000) table. With 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 the vehicle within the Conditions For Running DTC, located in appropriate DTC test. Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this procedure for any additional required DTCs that have not run. With scan tool, observe the I/M System Status display. Did the HO2S/O2S System Status update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S21852857482003062800000) .
5. With scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

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

1. The start-up Engine Coolant Temperature (ECT) is less than 122°F (50°C).
2. The start-up Intake Air Temperature (IAT) is less than 122°F (50°C).
3. Difference between the IAT and ECT is less than 14°F (8°C).
4. Battery voltage is 11-18 volts.

1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155898-S37237432342003062800000) .
2. After verifying the enable criteria, turn OFF the ignition for about 5 minutes to allow the sensors to cool before continuing with the test. Preprogram scan tool with the vehicle information before the ignition is turned ON. Ensure that the vehicle is within the «CONDITIONS FOR RUNNING»(ref-155898-S37366593532003062800000) . Set the vehicle parking brake. Verify that the transmission is in Park for automatic transmissions and Neutral for manual transmissions. Turn OFF all of the accessories (e.g., A/C, blower fan, etc.). Start engine and allow the engine to idle for 2 minutes or until the I/M System Status indicator updates to YES. Did the HO2S Heater System Status update to YES? If yes, go to step 5 . If no, go to next step.
3. With scan tool, observe the DTC Information. Does scan tool indicate any failed DTCs? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
4. To determine which DTCs are required to run in order to complete this test, see «INSPECTION/MAINTENANCE SYSTEM DTCS»(ref-155898-S08605071532003062800000) table. With 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 the vehicle within the Conditions For Running DTC, located in appropriate DTC test. Repeat the procedure until scan tool indicates the diagnostic test has run. Repeat this procedure for any additional required DTCs that have not run. With scan tool, observe the I/M System Status display. Did the HO2S Heater System Status update to YES? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S18072936342003062800000) .
5. With scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does scan tool indicate any Emission Related DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The HO2S Heater Tests will normally run within the 2 minutes allotted in the procedure. If there is an indeterminate condition, the test may take up to 8 minutes on some vehicles before a decision of pass or fail is made. If the test does not update within the allotted period of time, continue operation within the enable conditions until the test updates to YES. If the test does not update to YES, it may have failed or aborted due to the loss of enabling conditions. Extremely high ambient temperatures may prevent the HO2S Heater Test from initiating. The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the Malfunction Indicator Light (MIL) is requested. The I/M System Status also registers the number of Diagnostic Trouble Code (DTC). 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.

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DIAGNOSTIC TROUBLE CODE DEFINITIONS

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1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Inspect fuse that supplies voltage to the MIL. Is fuse open? If yes, go to step 10 . If no, go to next step.
3. Turn ignition off. Disconnect the PCM. See «COMPONENT LOCATIONS»(ref-155898-S01562465142003062800000) . Turn ignition on, with engine off. Connect a 3-amp fused jumper wire between the MIL control circuit and a good ground. Observe the MIL. Is the MIL illuminated? If yes, go to step 9 . If no, go to next step.
4. Did the fuse in the jumper wire open? If yes, go to step 11 . If no, go to next step.
5. Remove the Instrument Panel Cluster (IPC). See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Test the MIL control circuit for an open between the PCM and the IPC and repair as necessary. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
6. Probe the MIL battery positive voltage circuit at the IPC harness connector with a test light connected to a good ground. Does the test light illuminate? If yes, go to step 8 . If no, go to next step.
7. Repair open in the MIL battery positive voltage circuit. After repairs, go to step 14 .
8. Inspect for poor connections at the harness connector of the IPC and repair as necessary. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
9. Inspect for poor connections at the harness connector of the PCM and repair as necessary. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
10. Repair short to ground in the MIL battery positive voltage circuit. Replace fuse. After repairs, go to step 14 .
11. Repair short to voltage in the MIL control circuit. After repairs, go to step 14 .
12. Repair or replace the IPC. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step 14 .
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

If the problem is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition off. Disconnect the PCM. See «COMPONENT LOCATIONS»(ref-155898-S01562465142003062800000) . Turn ignition on, with engine off. Observe the MIL. Is the MIL illuminated? If yes, go to next step. If no, go to step 5 .
3. Remove the Instrument Panel Cluster (IPC). See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Test the MIL control circuit for a short to ground between the PCM and the IPC. Did you find and correct the condition? If yes, go to step 6 . If no, go to next step.
4. Repair or replace the IPC. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step 6 .
5. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
6. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

DIAGNOSTIC TESTS

Note. Before clearing DTCs, perform powertrain diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. Record FREEZE FRAME and FAILURE RECORDS for reference during testing. Data will be erased when DTCs are cleared. If PCM is replaced, NEW PCM must be programmed using special manufacturer's equipment.

Conditions For Running DTC

Engine is running.

Conditions For Setting DTC

1. PCM detects an electrical malfunction in the camshaft position actuator solenoid high control or low reference circuits.
2. The condition is present for more than 0.25 seconds.

Action Taken When DTC Sets

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

Conditions For Clearing MIL/DTC

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start engine. Allow engine to reach operating temperature. Increase engine speed to 1500 RPM. Using scan tool, command the cam phaser to 90 percent. Does the Cam Phase Actual parameter match the Cam Phase Angle Desired parameter? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the camshaft position actuator solenoid connector. Turn ignition on, with engine off. With a DVOM, measure voltage between the camshaft position actuator solenoid high control circuit and a good ground. Does the DVOM display voltage at battery voltage? If yes, go to next step. If no, go to step 7 .
5. Connect a test light between the camshaft position actuator solenoid high control circuit and ground. Does the test light illuminate? If yes, go to step 9 . If no, go to next step.
6. Connect a test light between the low reference circuit and battery positive. Does the test light illuminate? If yes, go to step 11 . If no, go to step 8 .
7. Test the camshaft position actuator solenoid high control circuit for an open or short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
8. Test the low reference circuit for an open. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
9. Test the camshaft position actuator solenoid high control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
10. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Inspect for poor connections at the harness connector of the camshaft position actuator solenoid. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to step 14 .
13. Replace camshaft position actuator solenoid. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S18792517682003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. Engine is running.
2. PCM has enabled the cam phaser.

1. Vehicle must be driven.
2. Difference between the desired CAM phase angle and the actual CAM phase angle is more than 1.5 degrees.
3. The CAM phaser is steady for 20 seconds.
4. Condition is present for 20 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Start and idle the engine for 2 minutes. Increase engine speed to 1500 RPM. With scan tool, command the cam phase solenoid from zero to 100 percent. Does the Cam Phase Angle Actual remain close to the Cam Phase Angle Desired at all commanded positions? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Operate the vehicle within the Conditions For Running DTC or as close the Freeze Frame/Failure Records data that you observe. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S08041510082003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent.
4. Let engine idle. Does the engine run rough or stall? If yes, go to step 9 . If no, go to next step.
5. Turn ignition off. Let vehicle sit for one minute. Check engine oil level. Is engine oil level within operating range? If yes, go to next step. If no, add oil to bring oil level to correct operating range.
6. Install an oil pressure gauge. Start engine. Increase engine speed to 1400 RPM. Observe engine oil pressure. Does the oil pressure gauge indicate engine oil pressure less than 28 psi? If yes, diagnose low oil pressure. See appropriate article in ENGINES. If no, go to next step.
7. Increase engine RPM to 1500 RPM. With scan tool, command the cam phase solenoid from zero percent to 100 percent. Does the Cam Phase Angle Actual increment at all? If yes, go to next step. If no, go to step 10 .
8. Turn ignition off. Disconnect the camshaft position actuator solenoid connector. With a DVOM, measure the resistance of the camshaft position actuator solenoid valve assembly. Does the resistance measure 8-12 ohms? If yes, go to step 13 . If no, go to step 20 .
9. Turn ignition off. Disconnect the camshaft position actuator solenoid connector. Probe the camshaft position actuator solenoid high control circuit with a test light connected to good ground. Start engine. With scan tool, command the cam phase solenoid between 0-50 percent. Does the test light turn ON and OFF? If yes, go to next step. If no, go to step 15 .
10. Turn ignition off. Remove the camshaft position solenoid valve assembly from the engine block. Inspect the camshaft position actuator solenoid valve assembly for the following: Torn screens. Debris on the screens. Debris clogging the oil ports. Missing screens. Oil seepage at the solenoid connector pins. Did you find a problem? If yes, go to step 20 . If no, go to next step.
11. Connect a jumper wire between battery ground and the camshaft position actuator low control at the solenoid. Connect a fused jumper wire between battery voltage and the camshaft position actuator high control at the solenoid. Momentarily touch the fused jumper to the battery voltage. Observe the spool valve inside the camshaft position actuator. Does the spool valve move from fully closed to fully opened? If yes, go to next step. If no, go to step 18 .
12. Inspect for the following conditions: Excessive timing chain play. Excessive camshaft end play. Excessive crankshaft end play. Proper installation of the camshaft position actuator assembly. See appropriate article in ENGINES. Repair as necessary. After repairs, go to step 22 .
13. Disconnect the PCM. With a DVOM measure the resistance on the camshaft position actuator high control circuit. Does the resistance measure more than 5 ohms? If yes, go to step 16 . If no, go to next step.
14. Measure the resistance on the low reference circuit with a DVOM. Does the resistance measure more than 5 ohms? If yes, go to step 17 . If no, see appropriate article in ENGINES.
15. Test the camshaft position actuator high control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 18 .
16. Repair high resistance on the camshaft position actuator high control circuit. After repairs, go to step 22 .
17. Repair high resistance on the camshaft position actuator low reference circuit. After repairs, go to step 22 .
18. Test for an intermittent and for a poor connection at the camshaft position actuator solenoid valve assembly. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
19. Test for an intermittent and for a poor connection at the PCM. Did you repair the circuit? If yes, go to step 22 . If no, go to step 21 .
20. Replace camshaft position actuator solenoid. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 22 .
21. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
22. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S08041510082003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
23. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTC P0107, P0108, P0116, P0117, P0118, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0340, P0341, P0351, P0352, P0353, P0354, P0355, P0356, P0440, P0442, P0446, P0452, P0453, P0502, P0506, P0507, P0740, P0741, P0742, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1512, P1514, P1515, P1516, P1635, P1639, P1680, P1681, or P1860 not set.
2. Engine run time is more than 40 seconds.
3. The change in engine speed is stable to within 50 RPM.
4. Engine speed is 600-6375 RPM.
5. Torque Converter Clutch (TCC) is stable to within 2.5 percent.
6. All conditions stable for 1.5 seconds.

The actual MAP sensor signal is not within the predicted range for 14 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Inspect for the following conditions: MAP sensor seal missing or damaged. Restrictions in the MAP sensor vacuum source. Vacuum hoses disconnected, damaged, or incorrectly routed. Vacuum leaks between the intake manifold and the engine. Vacuum leaks at the throttle body. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
3. Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool? If yes, go to next step. If no, go to step 5 .
4. Install scan tool. Turn ignition on, with engine off. Monitor scan tool and record the MAP sensor pressure. Compare the MAP sensor pressure to that of a known-good vehicle. Is the pressure difference between the vehicles less than 0.89 in. Hg (3 kPa)? If yes, go to next step. If no, go to step 11 .
5. Turn ignition on, with engine off. Observe the MAP sensor pressure with a scan tool. Refer to Altitude vs Barometric Pressure in «SENSOR OPERATING RANGE CHARTS - TRUCKS»(ref-159155) article. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP sensor indicate the correct barometric pressure? If yes, go to next step. If no, go to step 11 .
6. Observe the MAP sensor pressure on scan tool. Start the engine. Does the MAP sensor value change? If yes, go to next step. If no, go to step 11 .
7. Turn ignition off. Remove the MAP sensor from the vacuum source. Leave the electrical harness connected. Connect a hand-held vacuum pump to the MAP sensor. Turn ignition on, with engine off. Observe the MAP sensor pressure as you SLOWLY apply vacuum 1 in. Hg at a time. Each inch of vacuum should result in a 0.89-1.18 in. Hg (3-4 kPa) drop in the MAP sensor pressure. Increase the vacuum to 20 in. Hg (67 kPa). Does scan tool indicate that the MAP sensor pressure decreases smoothly through the test? If yes, go to next step. If no, go to step 11 .
8. Observe the MAP sensor pressure with 20 in. Hg (67 kPa) of vacuum applied to the MAP sensor. Does scan tool indicate that the MAP sensor pressure is less than 10 in. Hg (34 kPa)? If yes, go to next step. If no, go to step 11 .
9. Observe the MAP sensor pressure with the scan tool. Disconnect vacuum pump from the MAP sensor. Does the MAP sensor pressure return to the original reading observed in step 4 or 5 ? If yes, go to next step. If no, go to step 23 .
10. Inspect for incorrect cam timing, restricted exhaust flow, or worn piston rings. Did you find and correct the condition? If yes, go to step 25 . If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
11. Disconnect MAP sensor electrical connector. Observe MAP sensor voltage with scan tool. Is voltage less than 0.3 volt? If yes, go to next step. If no, go to step 16 .
12. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DVOM. Is voltage more than 5.2 volts? If yes, go to step 17 . If no, go to next step.
13. Probe the 5-volt reference circuit of the MAP sensor with a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 18 .
14. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the MAP sensor and the signal circuit of the MAP sensor. Does scan tool indicate that the MAP sensor voltage is more than 4.9 volts? If yes, go to next step. If no, go to step 19 .
15. Turn ignition off. Remove jumper wire. Connect a jumper wire between each of the terminals in the MAP sensor harness connector and corresponding terminal at the MAP sensor. Turn ignition on, with engine off. Measure voltage from the low reference circuit of the MAP sensor at the jumper wire terminal to a good ground with a DVOM. Is the voltage more than 0.2 volt? If yes, go to step 20 . If no, go to step 21 .
16. Test the MAP sensor signal circuit between PCM and MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
17. Test all of the branches of the 5-volt reference circuit that are shared with the MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
18. Test the low reference circuit of the MAP sensor for high resistance or an open. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 22 .
19. Test the MAP sensor signal circuit between the PCM and MAP sensor for a short to ground, open or high resistance. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 22 .
20. Test the low reference circuit between the PCM and MAP sensor for an open or for high resistance. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 22 .
21. Test for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 23 .
22. Inspect the MAP sensor for intermittent or poor connections. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
23. Replace MAP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 26 .
24. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
25. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S12943256182003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
26. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0122 or P0123 not set.
2. Engine speed is less than 1000 RPM; or, the engine speed is more than 1000 RPM, the Throttle Position (TP) is more than 28 percent, and the pedal position is more than 1.2 percent.

The MAP sensor voltage is less than 0.2 volts for at least 6.25 seconds.

1. PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. PCM will store the conditions which were present when the DTC set as Freeze Frame/Failure Records data.
3. A history DTC is stored.
4. PCM will substitute a default MAP value to control the fuel delivery. The scan tool will not show the defaulted value.
5. Engine will operate in Open Loop when the vehicle is traveling under 5 MPH.
6. Engine will operate in Closed Loop when the vehicle is traveling over 5 MPH.

1. The PCM will turn the Malfunction Indicator Light (MIL) OFF after 3 consecutive drive trips that the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start engine. Monitor the Diagnostic Trouble Code (DTC) Information using scan tool. Does scan tool indicate that DTC P1639 is current? If yes, see «DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT»(ref-155898-S02536990042003062800000) . If no, go to next step.
3. With scan tool, observe the MAP sensor voltage. Does scan tool indicate that the voltage is less than 0.2 volt? If yes, go to step 5 . If no, go to next step.
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S22868522322003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Turn ignition off. Disconnect MAP sensor electrical connector. Turn ignition on, with engine off. Probe the 5-volt reference circuit of the MAP sensor with a test light connected to a good ground. Is the test light OFF? If yes, go to step 7 . If no, go to next step.
6. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the MAP sensor and the signal circuit of the MAP sensor. Does scan tool indicate that the MAP sensor voltage is about 5 volts? If yes, go to step 9 . If no, go to step 8 .
7. Test the 5-volt reference circuit of the MAP sensor for a short to ground or an open. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
8. Test the signal circuit of the MAP sensor for a short to ground or an open. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 10 .
9. Inspect for intermittent or poor connections at MAP sensor. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 11 .
10. Inspect for intermittent or poor connections at PCM. Did you find and correct the condition? If yes, go to step 13 . If no, go to step 12 .
11. Replace MAP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 13 .
12. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
13. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S22868522322003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
14. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0122 or P0123 not set.
2. Throttle Position (TP) is less than 15 percent.
3. Vehicle speed is less than one MPH.
4. Engine run time is more than 20-40 seconds.

The MAP sensor voltage is more than 4.2 volts for at least one second.

1. The PCM illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. PCM will store the conditions which were present when the DTC set as Freeze Frame/Failure Records data.
3. A history DTC is stored.
4. The PCM will substitute a defaulted MAP value to control the fuel delivery. The scan tool will not show the defaulted value.
5. Engine will operate in Open Loop when the vehicle is traveling under 5 MPH.
6. Engine will operate in Closed Loop when the vehicle is traveling over 5 MPH.

1. PCM will turn the Malfunction Indicator Light (MIL) OFF after 3 consecutive drive trips that the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Start engine. Let engine idle. Does scan tool indicate that the MAP sensor voltage is greater than 4.2 volts? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S08265220592003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S09391599932003062800000) .
4. Turn ignition off. Inspect the MAP sensor vacuum source for leaks, restrictions, or faulty connections. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
5. Start engine. Monitor the Diagnostic Trouble Code (DTC) Information with the scan tool. Is DTC P1639 also set? If yes, go to step 8 . If no, go to next step.
6. Turn ignition off. Disconnect the MAP sensor electrical connector. Turn ignition on, with engine off. Observe the MAP sensor parameter with the scan tool. Is the voltage less than 0.2 volts? If yes, go to next step. If no, go to step 9 .
7. Turn ignition off. Connect a jumper wire between each of the terminals in the MAP sensor harness connector and the corresponding terminal at the MAP sensor. Turn ignition on, with engine off. Measure the voltage from the low reference circuit of the MAP sensor at the jumper wire terminal to a good ground with the DVOM. Is the voltage more than 0.2 volt? If yes, go to step 10 . If no, go to step 11 .
8. Turn ignition off. Disconnect the MAP sensor electrical connector. Turn ignition on, with engine off. Observe the MAP sensor parameter with the scan tool. Is the voltage less than 0.2 volt? If yes, go to «DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT»(ref-155898-S02536990042003062800000) . If no, go to next step.
9. Test the MAP sensor signal circuit between PCM and MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
10. Test the low reference circuit between the PCM and MAP sensor for high resistance or for an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
11. Inspect for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Inspect for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
13. Replace MAP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 15 .
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S08265220592003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
16. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The 5-volt reference circuits used by the various engine control components are internally connected in the PCM. If a component's 5-volt reference circuit is shorted to voltage, the other 5-volt reference circuits may be affected.
2. Inspect the MAP sensor vacuum source for leaks, restrictions, or poor connections.
3. This DTC may set as the result of a misfire.
4. If an intermittent condition exists, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. DTCs P0116, P0117, P0118, P0125, P0128, P0502, or P0503 not set.
2. Engine run time is more than 320 seconds.
3. Vehicle speed sensor indicates that vehicle speed is more than 15 MPH.

The IAT is more than 262°F (128°C) for more than 6 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Install scan tool. Turn ignition on, with engine off. Observe the IAT sensor temperature with scan tool. Is the IAT sensor temperature more than 262°F (128°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S41390969202003062800000) . Does the DTC reset? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the IAT sensor. Turn ignition on, with engine off. Observe the IAT sensor temperature with scan tool. Is the IAT sensor temperature less than -38°F (-39°C)? If yes, go to step 7 . If no, go to next step.
5. Test the signal circuit of the IAT sensor for a short to ground or a short to IAT low reference circuit and repair as necessary. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
6. Test for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
7. Replace IAT sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 10 .
8. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
9. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
10. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S41390969202003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
11. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0116, P0117, P0118, P0125, P0128, P0502, or P0503 not set.
2. Engine run time is more than 320 seconds.
3. Vehicle speed sensor indicates that vehicle speed is less than 15 MPH.

The IAT sensor signal voltage indicates that the intake air temperature is less than -38°F (-39°C) for more than 3 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Install scan tool. Turn ignition on, with engine off. Observe the IAT sensor temperature with scan tool. Is the IAT sensor temperature less than -36°F (-38°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S02690237962003062800000) . Does the DTC reset? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Disconnect IAT sensor. Connect a DVOM between the signal circuit of the IAT sensor and a good ground. Is the voltage more than 5.2 volts? If yes, go to next step. If no, go to step 6 .
5. Test the signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
6. Connect a 3-amp fused jumper wire between the signal circuit of the IAT sensor and the low reference circuit of the IAT sensor. Observe the IAT sensor parameter with a scan tool. Is the IAT sensor parameter more than 262°F (128°C)? If yes, go to step 10 . If no, go to next step.
7. Connect a 3-amp fused jumper wire between the signal circuit of the IAT sensor and a good ground. Observe the IAT sensor parameter with a scan tool. Is the IAT sensor parameter more than 262°F (128°C)? If yes, go to step 9 . If no, go to next step.
8. Test the signal circuit of the IAT sensor for an open circuit or high resistance. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
9. Test the IAT sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
10. Test the IAT sensor circuit for a short to any 5-volt reference circuit. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
11. Test for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
13. Replace IAT sensor. After replacing sensor, go to step 15 .
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S02690237962003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
16. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Engine has been running more than 2 minutes.

PCM detects that the ECT sensor parameter is more than 280°F (138°C) for more than 6 seconds.

1. The control module illuminates the Malfunction Indicator Light (MIL) if a failure is detected during 2 consecutive key cycles.
2. The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in scan tool Freeze Frame/Failure Records.

1. The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
2. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 40°F (22°C) from the start-up coolant temperature and the engine coolant reaches a temperature that is more than 158°F (70°C) during the same ignition cycle.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Turn ignition on, with engine off. Observe the ECT sensor temperature display. Does scan tool indicate that the ECT sensor temperature is greater than 280°F (138°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S38250093212003062800000) . Does the DTC reset? If yes, go to next step. If no, problem is intermittent.
4. Disconnect the ECT sensor. Turn ignition on, with engine off. With scan tool, observe the ECT sensor temperature. Does scan tool indicate that the ECT sensor temperature is less than -36°F (-38°C)? If yes, go to step 6 . If no, go to next step.
5. Turn ignition off. Disconnect the PCM. Test the signal circuit of the ECT sensor for a short to ground or a short to any low reference circuit. Did you find and correct the condition? If yes, go to step 10 . If no, go to step 8 .
6. Test for an intermittent and for a poor connection at the ECT sensor. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
7. Replace ECT sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 10 .
8. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 10 . If no, go to next step.
9. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
10. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S38250093212003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
11. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The engine has been running more than 60 seconds.

The ECT sensor temperature is less than 122°F (50°C) for more than 6 seconds.

1. The control module illuminates the Malfunction Indicator Light (MIL) if a failure is detected during 2 consecutive key cycles.
2. The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in scan tool Freeze Frame/Failure Records.

1. The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
2. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 40°F (22°C) from the start-up coolant temperature and the engine coolant reaches a temperature that is more than 158°F (70°C) during the same ignition cycle.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Turn ignition on, with engine off. With scan tool, observe the ECT sensor temperature. Does scan tool indicate that the ECT sensor temperature is less than -36°F (-38°C)? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S37405841152003062800000) . Does the DTC reset? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Disconnect the ECT sensor. Measure the voltage from the signal circuit of the ECT sensor to a good ground with a DVOM. Is the voltage more than 5.2 volts? If yes, go to next step. If no, go to step 6 .
5. Test the ECT sensor signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
6. Connect a 3-amp fused jumper between the signal circuit of the ECT sensor and low reference circuit. Observe the ECT sensor parameter with scan tool. Is the ECT sensor parameter more than 280°F (138°C)? If yes, go to step 10 . If no, go to next step.
7. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a good ground. Observe the ECT sensor parameter with a scan tool. Is the ECT sensor parameter more than 280°F (138°C)? If yes, go to step 9 . If no, go to next step.
8. Test the signal circuit of the ECT sensor for a high resistance or an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
9. Test the ECT sensor low reference circuit for a high resistance or an open. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
10. Test the ECT sensor signal circuit for a short to any 5-volt reference circuit. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
11. Test for an intermittent and for a poor connection at the ECT sensor. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
13. Replace ECT sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 15 .
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S37405841152003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
16. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The ignition switch is in the crank or run position.
2. DTC P1635 is not set.
3. The ignition voltage is more than 5.23 volts.

The TP sensor 1 and 2 voltages are not within a calibrated range.

1. PCM will illuminate the Malfunction Indicator Light (MIL) during the first trip in which the diagnostic runs and fails.
2. PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

1. PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are DTCs P1120 and P1220 set? If yes, see «DTC P1120: THROTTLE POSITION SENSOR 1 CIRCUIT»(ref-155898-S42779905142003062800000) and «DTC P1220: THROTTLE POSITION SENSOR 2 CIRCUIT»(ref-155898-S02577458542003062800000) . If no, system is okay.

The DTC indicates 2 separate faults, one fault with TP sensor 1 and one fault with TP sensor 2. The DTC P1120 diagnostic test along with the DTC P1220 diagnostic test may need to be followed to find both faults. See DTC P1120: THROTTLE POSITION SENSOR 1 CIRCUIT and DTC P1220: THROTTLE POSITION SENSOR 2 CIRCUIT .

1. The ignition switch is in the crank or run position.
2. DTC P1635 is not set.
3. The ignition voltage is more than 5.23 volts.

The TP sensor 1 and 2 voltages are not within a calibrated range.

1. PCM will illuminate the Malfunction Indicator Light (MIL) during the first trip in which the diagnostic runs and fails.
2. PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

1. The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are DTCs P1120 and P1220 set? If yes, see «DTC P1120: THROTTLE POSITION SENSOR 1 CIRCUIT»(ref-155898-S42779905142003062800000) and «DTC P1220: THROTTLE POSITION SENSOR 2 CIRCUIT»(ref-155898-S02577458542003062800000) . If no, system is okay.

The DTC indicates 2 separate faults, one fault with TP sensor 1 and one fault with TP sensor 2. The DTC P1120 diagnostic test along with the DTC P1220 diagnostic test may need to be followed to find both faults. See DTC P1120: THROTTLE POSITION SENSOR 1 CIRCUIT and DTC P1220: THROTTLE POSITION SENSOR 2 CIRCUIT .

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0171, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0335, P0336, P0440, P0442, P0446, P0452, P0453, P0480, P0502 and P0503 (A/T only), P0601, P0602, P0604, P0606, P0621, P1133, or P1441 not set.
2. Engine has run more than 30 seconds and for less than 20 minutes.
3. The minimum Intake Air Temperature (IAT) is more than 19°F (-7°C).
4. Engine coolant temperature at start-up is less than 104°F (40°C).
5. Vehicle has traveled more than 0.5 miles at more than 25 MPH (40 km/h).
6. Mass Airflow (MAF) calculated is more than 15 g/s.

1. The average air flow is more than 20 g/s.
2. The vehicle has traveled more than 0.5 miles over 25 MPH.
3. Enough air flow has entered the engine and the engine coolant temperature has not risen to 104°F (40°C) for 60 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Is the cooling system low on coolant? If yes, locate and repair source of coolant loss and refill system. If no, go to next step.
3. Test and verify the proper operation of the thermostat. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
4. Disconnect the ECT sensor. Inspect for corrosion on the ECT sensor terminals, improper or corroded terminals at the ECT harness connector, or loose terminals in the ECT harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
5. Measure the voltage from the signal circuit of the ECT sensor to a good ground with a DVOM. Is the voltage within 4.8-5.2 volts? If yes, go to next step. If no, go to step 8 .
6. Measure the voltage from the signal circuit of the ECT sensor to the low reference circuit of the ECT sensor with a DVOM. Is the voltage within 4.8-5.2 volts? If yes, go to step 9 . If no, go to next step.
7. Test the ECT sensor low reference circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
8. Test the ECT sensor signal circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
9. Turn ignition off. Remove the ECT sensor. Place the sensor on a work surface away from any heat source. Allow the sensor to reach the ambient air temperature for 30-60 minutes. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. Measure the resistance of the ECT sensor and record the value. Compare the resistance measurement of the ECT sensor to the ambient air temperature on the Temperature vs. Resistance table. Refer to «SENSOR OPERATING RANGE CHARTS - TRUCKS»(ref-159155) article. Is the resistance measurement of the ECT sensor within the specified range? If yes, go to next step. If no, go to step 12 .
10. Install the ECT sensor. After reinstalling sensor, check for an intermittent problem. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
11. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace ECT sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to next step.
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0335, P0336, P0440, P0442, P0446, P0452, P0453, P0480, P0502 and P0503 (A/T only), P0601, P0602, P0604, P0606, P0621, P1133, or P1441 not set.
2. The engine coolant temperature is more than -38°F (-39°C), but less than 158°F (70°C).
3. Intake air temperature is more than 19°F (-7°C).
4. Engine is running between 30 seconds and 30 minutes.
5. Vehicle has traveled more than 1.5 miles at more than 25 MPH (40 km/h).
6. Mass Airflow (MAF) calculated is more than 15 g/s.

1. The average air flow is more than 20 g/s.
2. The vehicle has traveled more than 1.5 miles over 25 MPH.
3. Enough air flow has entered the engine and the engine coolant temperature has not risen to 176°F (80°C) for 30 seconds.

1. The control module illuminates the Malfunction Indicator Light (MIL) if a failure is detected during 2 consecutive key cycles.
2. The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in scan tool Freeze Frame/Failure Records.

1. The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
2. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 40°F (22°C) from the start-up coolant temperature and the engine coolant reaches a temperature that is more than 158°F (70°C) during the same ignition cycle.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Is the cooling system low on coolant? If yes, locate and repair source of coolant loss and refill system. If no, go to next step.
3. Test and verify the proper operation of the thermostat. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
4. Disconnect the ECT sensor. Inspect for corrosion on the ECT sensor terminals, improper or corroded terminals at ECT harness connector, or loose terminals in the ECT harness connector. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
5. Measure the voltage from the signal circuit of the ECT sensor to a good ground with a DVOM. Is the voltage within 4.8-5.2 volts? If yes, go to next step. If no, go to step 8 .
6. Measure the voltage from the signal circuit of the ECT sensor to the low reference circuit of the ECT sensor with a DVOM. Is the voltage within 4.8-5.2 volts? If yes, go to step 9 . If no, go to next step.
7. Test the ECT sensor low reference circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
8. Test the ECT sensor signal circuit for high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 11 .
9. Turn ignition off. Remove the ECT sensor. Place the sensor on a work surface away from any heat source. Allow the sensor to reach the ambient air temperature for 30-60 minutes. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. Measure the resistance of the ECT sensor and record the value. Compare the resistance measurement of the ECT sensor to the ambient air temperature on the Temperature vs. Resistance table. See «SENSOR OPERATING RANGE CHARTS - TRUCKS»(ref-159155) article. Is resistance value is as specified? If yes, go to next step. If no, go to step 12 .
10. Install ECT sensor. After reinstalling sensor, check for an intermittent problem. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
11. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
12. Replace ECT sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to next step.
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S30376363072003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. Engine Run Time parameter is more than 200 seconds.
3. Engine Speed parameter is 1200-3400 RPM.
4. TP Indicated Angle parameter is 15-50 percent.
5. ECT Sensor parameter is more than 158°F (70°C).
6. APP Sensor Indicated Angle parameter is more than 1.2 percent.
7. Conditions met for 2 seconds.

Conditions For Setting The DTC

PCM detects that the Loop Status parameter is open for 12.5 seconds.

Action Taken When The DTC Sets

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

Conditions For Clearing The MIL/DTC

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. Command the HO2S 1 heater ON with a scan tool. Wait 15 seconds to allow the HO2S 1 heater current to stabilize. Observe the HO2S 1 heater current parameter with a scan tool. Is the HO2S 1 heater current parameter within 0.22-1.56 amps? If yes, go to next step. If no, go to «DTC P0135 OR P0141: HO2S HEATER CIRCUIT (BANK 1; SENSOR 1 OR 2)»(ref-155898-S07922565602003062800000) .
3. Start engine. Allow engine to reach operating temperature. Operate engine at 2000 RPM for 30 seconds. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter varying greater than and less than the specified range of 300-600 mV? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S31859224782003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Turn ignition off. Disconnect the HO2S 1. Turn ignition on, with engine off. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter more than 800 mV? If yes, go to next step. If no, go to step 7 .
6. Test the HO2S 1 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
7. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 1 harness connector on the engine harness side and the low signal circuit of the HO2S 1 harness connector on the engine harness side. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter within 400-500 mV? If yes, go to step 9 . If no, go to next step.
8. Remove the jumper wire used in previous step. Test the HO2S 1 heater low control circuit for a short to the HO2S 1 low signal circuit or HO2S 1 high signal circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 14 .
9. Remove the jumper wire used in previous step. Connect a 3-amp fused jumper wire from the high signal circuit of the HO2S 1 harness connector on the engine harness side and ground. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter within 400-500 mV? If yes, go to step 11 . If no, go to next step.
10. Remove the jumper wire used in previous step. Test the HO2S low signal circuit for an open. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
11. Measure the voltage from the high signal circuit of the HO2S 1 harness connector on the engine harness side to a good ground with a DVOM. Is the voltage more than 1.0 volt? If yes, go to next step. If no, go to step 13 .
12. Test the HO2S 1 low signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
13. Test the HO2S 1 high signal circuit for an open. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
14. Test for an intermittent and for a poor connection at the HO2S 1. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
15. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
16. Replace the HO2S 1. After replacing sensor, go to step 18 .
17. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
18. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S31859224782003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
19. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 Signal parameter is more than 10 volts.
4. Fuel level sensor parameter is more than 10 percent.
5. Engine Run Time parameter is more than 10 seconds.
6. Loop Status parameter is closed.
7. TP Indicated Angle parameter is between 15-50 percent.
8. MAP Sensor parameter is more than 7.4 in. Hg (25 kPa).
9. APP Sensor Indicated Angle parameter is more than 1.2 percent.
10. Conditions are met for 4 seconds.

The HO2S 1 signal voltage is less than 52 mV for 125 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate the engine at normal operating temperature. Operate the engine more than 1200 RPM for 2 minutes. Observe the HO2S 1 voltage parameter with a scan tool. Does the scan tool indicate that HO2S 1 voltage is less than 52 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S32808207682003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S 1 high signal circuit on the PCM side with a DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 1 high signal circuit for a short to ground or a short to the HO2S 1 low signal circuit. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 1 is detecting a lean condition or may be contaminated. Inspect HO2S connector water intrusion, silicone contamination, exhaust leak between HO2S 1 and engine, vacuum leaks, incorrect fuel pressure, or lean fuel injectors. Repair as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 1 sensor. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace the HO2S 1. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to step 11 .
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S32808207682003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Rich Test Enable

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 Signal parameter is more than 10 volts.
4. Fuel Level Sensor parameter is more than 10 percent.
5. Engine Run Time parameter is more than 10 seconds.
6. Loop Status parameter is closed.
7. TP Indicated Angle parameter is between 15-50 percent.
8. APP Sensor Indicated Angle parameter is more than 1.2 percent.
9. MAP Sensor parameter is more than 7.4 in. Hg (25 kPa).
10. Conditions are met for 4 seconds.

Decel Fuel Cutoff Test Enable

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. Loop Status parameter is closed.
3. Decel Fuel Cutoff is active for more than 2.5 seconds.

Rich Test

1. PCM detects that the HO2S 1 parameter is more than 946 mV for 50 seconds.

Decel Fuel Cutoff Test Enable

1. PCM detects that the HO2S 1 parameter is more than 1042 mV for 50 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.
4. The vehicle will operate in Open Loop operation.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate engine at normal operating temperature. Operate engine at more than 1200 RPM for 2 minutes. Observe the HO2S 1 voltage parameter with a scan tool. Does the scan tool indicate that the HO2S voltage is more than 946 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S21768309172003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 1 sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S 1 high signal circuit on the PCM side with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 1 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 1 is detecting a rich condition or may be contaminated. Inspect HO2S connector for water intrusion, silicone-contaminated HO2S 1, fuel contaminated engine oil, incorrect fuel pressure, inaccurate MAP sensor, leaking fuel pressure regulator, or rich fuel injectors. Repair any of the conditions as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 1 sensor. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace the HO2S 1. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S21768309172003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 Signal parameter is more than 10 volts.
4. Fuel Level Sensor parameter is more than 10 percent.
5. Engine Run Time parameter is more than 200 seconds.
6. Engine Speed parameter is 1000-2500 RPM.
7. MAP Sensor parameter is 7.4-30.1 in. Hg (25-104 kPa).
8. Air Flow Calculated parameter is more than 16 g/s.
9. Loop Status parameter is closed.
10. TP Indicated Angle parameter is 5-30 percent.
11. EVAP Purge Solenoid command is more than 10 percent.
12. Conditions have been met for 60 seconds.

PCM detects that the HO2S 1 rich-to-lean or lean-to-rich average response time is more than a calibrated value.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate the engine at normal operating temperature. Operate the engine at more than 1200 RPM for 2 minutes. Observe the HO2S 1 voltage parameter with a scan tool. Does the scan tool indicate that the HO2S 1 voltage is varying greater than and less than 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S24727071722003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. Refer to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 1. Turn ignition on, with engine off. Measure the voltage of the HO2S 1 high signal circuit on the PCM side to a good ground with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to next step. If no, go to step 9 .
5. Turn ignition off. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit and the HO2S 1 low signal circuit. Turn ignition on. Monitor the HO2S 1 voltage for the sensor that applies to this DTC with the scan tool. Does the scan tool indicate that the HO2S 1 voltage is less than 20 mV? If yes, go to next step. If no, go to step 10 .
6. Turn ignition off. Remove the 3-amp fused jumper wire. Connect a test light between the ignition 1 voltage circuit and a good ground. Do not use the HO2S 1 heater low control. Turn ignition on, with engine off. Does the test light illuminate? If yes, go to next step. If no, go to step 11 .
7. Connect a test light between the ignition 1 voltage circuit and the HO2S 1 heater low control circuit. Turn ignition on, with engine off. Command the HO2S 1 heater ON and OFF with a scan tool. Does the test light turn ON and OFF with each command? If yes, go to step 14 . If no, go to next step.
8. Does the test light remain illuminated with each command? If yes, go to step 12 . If no, go to step 13 .
9. Test the HO2S 1 high signal circuit for open, high resistance, short to ground, or short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
10. Test the HO2S 1 low signal circuit for an open, a high resistance, or a short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
11. Test the ignition 1 voltage circuit for an open, high resistance, or short to ground. Replace the O2 fuse if necessary. Did you find and correct the condition? If yes, go to step 19 . If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
12. Test the HO2S 1 low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
13. Test the HO2S 1 low control circuit for an open, a high resistance, or a short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
14. Inspect for use of incorrect silicone RTV sealant, fuel contamination, exhaust leak, HO2S installed incorrectly, or damaged wiring. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
15. Inspect for poor connections at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
16. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 18 .
17. Replace HO2S 1. After replacing sensor, go to step 19 .
18. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
19. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S24727071722003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
20. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 Signal parameter is more than 10 volts.
4. Fuel level parameter is more than 10 percent.
5. Air Flow Calculated parameter is more than 7 g/s.
6. TP Indicated Angle parameter is 15-50 percent.
7. MAP Sensor parameter is more than 7.4 in. Hg (25 kPa).
8. APP Sensor Indicated Angle parameter is more than 1.2 percent.
9. Engine Run Time parameter is more than 30 seconds.

PCM detects that the HO2S 1 parameter is between 400-500 mV for 125 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
2. PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
3. A history DTC stores.
4. The vehicle will operate in Open Loop operation.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. Command the HO2S 1 heater ON with a scan tool. Wait 15 seconds to allow the HO2S 1 heater current to stabilize. Observe the HO2S 1 heater current parameter with a scan tool. Is the HO2S 1 heater current parameter within 0.22-1.56 amps? If yes, go to next step. If no, go to «DTC P0135 OR P0141: HO2S HEATER CIRCUIT (BANK 1; SENSOR 1 OR 2)»(ref-155898-S07922565602003062800000) .
3. Start and allow engine to reach operating temperature. Operate engine at 2000 RPM for 30 seconds. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter varying greater than and less than 400-500 mV? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S41781300012003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Turn ignition off. Disconnect the HO2S 1. Turn ignition on, with engine off. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter more than 800 mV? If yes, go to next step. If no, go to step 7 .
6. Test the HO2S 1 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
7. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 1 harness connector on the engine harness side and the low signal circuit of the HO2S 1 harness connector on the engine harness side. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter within 400-500 mV? If yes, go to step 9 . If no, go to next step.
8. Remove the jumper wire used in previous step. Test the HO2S 1 heater low control circuit for a short to the HO2S 1 low signal circuit or the HO2S 1 high signal circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 14 .
9. Remove the jumper wire used in previous step. Connect a 3-amp fused jumper wire from the high signal circuit of the HO2S 1 harness connector on the engine harness side and ground. Observe the HO2S 1 voltage parameter with a scan tool. Is the HO2S 1 voltage parameter within 400-500 mV? If yes, go to step 11 . If no, go to next step.
10. Remove the jumper wire used in previous step. Test the HO2S 1 low signal circuit for an open. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
11. Measure the voltage from the high signal circuit of the HO2S 1 harness connector on the engine harness side to a good ground with a DVOM. Is the voltage more than 1.0 volt? If yes, go to next step. If no, go to step 13 .
12. Test the HO2S 1 low signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
13. Test the HO2S 1 high signal circuit for an open. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15
14. Test for an intermittent and for a poor connection at the HO2S 1. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
15. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
16. Replace the HO2S 1. After replacing sensor, go to step 18 .
17. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
18. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S41781300012003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
19. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. Ignition 1 signal parameter is 10-17 volts.
3. Engine Coolant Temperature (ECT) is more than 158°F (70°C).
4. The air flow calculated is less than 50 g/s.
5. The fuel level sensor is more than 10 percent.
6. The engine run time is more than 60 seconds.

PCM detects that the affected HO2S heater current is less than 0.22 amps or more than 1.56 amps for more than 200 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. Command the affected HO2S heater ON with a scan tool. Wait 15 seconds to allow the HO2S heater current to stabilize. Observe the affected HO2S heater current parameter with a scan tool. Is the HO2S heater current parameter within 0.22-1.56 amps? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S14503712212003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Inspect the O2 fuse. Is O2 fuse open? If yes, go to next step. If no, go to step 6 .
5. Test the ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 8 .
6. Disconnect the affected HO2S. Turn ignition on, with engine off. Probe the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side with a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 17 .
7. Connect a test light between the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side and the HO2S heater low control circuit of the HO2S harness connector on the engine harness side. Command the affected HO2S heater ON and OFF with a scan tool. Does the test light turn ON and OFF with each command? If yes, go to step 9 . If no, go to step 10 .
8. Test the ignition 1 voltage circuit on the sensor side of the HO2S connector for a short to ground. Is any sensor shorted to ground? If yes, go to step 18 . If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
9. Measure the resistance of the following circuits with a DVOM: HO2S heater low control circuit, and ignition 1 voltage circuit. Is the resistance of either circuit more than 3 ohms? If yes, go to step 16 . If no, go to step 14 .
10. Does the test light remain illuminated with each command? If yes, go to next step. If no, go to step 12 .
11. Test the HO2S heater low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 15 .
12. Test the HO2S heater low control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 20 . If no, go to next step.
13. Test the HO2S heater low control circuit for an open. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 15 .
14. Test for an intermittent and for a poor connection at the HO2S. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 18 .
15. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 19 .
16. Repair circuit with high resistance. After repairs, go to step 20 .
17. Repair open in the ignition 1 voltage circuit. After repairs, go to step 20 .
18. Replace HO2S. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 20 .
19. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
20. Were you sent to this diagnostic from DTC P0134? If yes, go to step 18 in DTC P0134. If no, go to next step.
21. Were you sent to this diagnostic from DTC P0140? If yes, go to step 18 in DTC P0140. If no, go to next step.
22. Replace the O2 fuse, if necessary. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S14503712212003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
23. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 signal parameter is more than 10 volts.
4. Fuel Level Sensor parameter is more than 10 percent.
5. Engine Run Time parameter is more than 10 seconds.
6. Loop Status parameter is closed
7. TP Indicated Angle parameter is between 15-50 percent.
8. MAP Sensor parameter is more than 7.4 in. Hg (25 kPa).
9. APP Sensor Indicated Angle parameter is more than 1.2 percent.
10. Conditions met for 4 seconds.

The HO2S 2 remains less than 43 mV for 150 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Warm engine to normal operating temperature. Operate engine at more than 1200 RPM for 2 minutes. Observe the HO2S 2 voltage parameter with the scan tool. Does the scan tool indicate that the HO2S 2 voltage is less than 43 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S23493011962003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 2 sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S 2 high signal circuit on the PCM side with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 2 high signal circuit for a short to ground or a short to the low signal circuit. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 2 may be detecting a lean exhaust condition. Check HO2S connector for water intrusion, exhaust leak between HO2S 2 and engine, vacuum leaks, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair any of the conditions as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 2 sensor. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace HO2S 2. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to step 11 .
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S23493011962003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 Signal parameter is more than 10 volts.
4. Fuel Level Sensor parameter is more than 10 percent.
5. Engine Run Time parameter is more than 10 seconds.
6. Loop Status parameter is closed.
7. TP Indicated Angle parameter is 15-50 percent.
8. MAP Sensor parameter is more than 7.4 in. Hg (25 kPa).
9. APP Sensor Indicated Angle parameter is more than 1.2 percent.
10. Conditions have been met for 4 seconds.

PCM detects that the HO2S 2 voltage is more than 1042 mV for 50 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Warm engine to normal operating temperature. Operate engine at more than 1200 RPM for 2 minutes. Observe the HO2S 2 voltage parameter with the scan tool. Does the scan tool indicate that the HO2S 2 voltage is more than 1042 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S17204281772003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 2 sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S 2 high signal circuit on the PCM side with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 2 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 2 is detecting a rich exhaust condition or may be contaminated. Inspect HO2S connector for water intrusion, a silicone-contaminated HO2S 2, fuel-contaminated engine oil, incorrect fuel pressure, leaking fuel pressure regulator, or rich fuel injectors. Repair any of the conditions as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 2. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace HO2S 2. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S17204281772003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Ignition 1 Signal parameter is more than 10 volts.
4. Fuel Level Sensor parameter is more than 10 percent.
5. Engine Run Time parameter is more than 10 seconds.
6. Air Flow Calculated parameter is more than 7 g/s.
7. TP Indicated Angle parameter is 15-50 percent.
8. MAP Sensor parameter is more than 7.4 in. Hg (25 kPa).
9. APP Sensor Indicated Angle parameter is more than 1.2 percent.
10. Loop Status parameter is closed.

PCM detects that the HO2S 2 parameter is 425-473 mV for 125 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. Command the HO2S 2 heater ON with a scan tool. Wait 15 seconds to allow the HO2S 2 heater current to stabilize. Observe the HO2S 2 heater current parameter with a scan tool. Is the HO2S 2 heater current parameter within 0.22-1.56 amps? If yes, go to next step. If no, go to «DTC P0135 OR P0141: HO2S HEATER CIRCUIT (BANK 1; SENSOR 1 OR 2)»(ref-155898-S07922565602003062800000) .
3. Start and allow engine to reach operating temperature. Operate engine at 2000 RPM for 30 seconds. Quickly cycle the throttle from closed throttle to wide open throttle 3 times while observing the HO2S 2 voltage parameter with a scan tool. Did the HO2S 2 voltage parameter change more than 200 mV? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S36713569752003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Turn ignition off. Disconnect the HO2S 2. Turn ignition on, with engine off. Observe the HO2S 2 voltage parameter with a scan tool. Is the HO2S 2 voltage parameter more than 800 mV? If yes, go to next step. If no, go to step 7 .
6. Test the HO2S 2 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
7. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 harness connector on the engine harness side and the low signal circuit of the HO2S 2 harness connector on the engine harness side. Observe the HO2S 2 voltage parameter with a scan tool. Is the HO2S 2 voltage parameter within 400-500 mV? If yes, go to step 9 . If no, go to next step.
8. Remove the jumper wire used in previous step. Test the HO2S 2 heater low control circuit for a short to the HO2S 2 low signal circuit or the HO2S 2 high signal circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 14 .
9. Remove jumper wire used in previous step. Connect a 3-amp fused jumper wire from the high signal circuit of the HO2S 2 harness connector on the engine harness side and ground. Observe the HO2S 2 voltage parameter with a scan tool. Is the HO2S 2 voltage parameter within 400-500 mV? If yes, go to step 11 . If no, go to next step.
10. Remove the jumper wire used in previous step. Test the HO2S 2 low signal circuit for an open. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
11. Measure the voltage from the high signal circuit of the HO2S 2 harness connector on the engine harness side to a good ground with a DVOM. Is the voltage more than 1.0 volt? If yes, go to next step. If no, go to step 13 .
12. Test the HO2S 2 low signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
13. Test the HO2S 2 high signal circuit for an open. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
14. Test for an intermittent and for a poor connection at the HO2S 2. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
15. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
16. Replace HO2S 2. After replacing sensor, go to step 18 .
17. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
18. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S36713569752003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
19. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201, P0202, P0203, P0204, P0300, P0325, P0341, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, or P1441 not set.
2. Engine Coolant Temperature (ECT) is 140-239°F (60-115°C).
3. Intake air temperature is -13 to 239°F (-25 to 115°C).
4. Manifold Absolute Pressure (MAP) is more than 7.7 in. Hg (26 kPa).
5. Vehicle speed is less than 82 MPH.
6. Engine speed is 550-3400 RPM.
7. Barometric pressure is more than 21.3 in. Hg (72 kPa).
8. Fuel ethanol composition is less than 88 percent.
9. Fuel level is more than 9.8 percent.

Fuel Trim Index is more than 20 percent.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Start engine and drive vehicle under normal conditions until the engine reaches operating temperature and is in closed loop. Turn engine off. Turn ignition on, with engine off. Review the Freeze Frame Records/Failure Records and record displayed data for this DTC. Does scan tool indicate that the Fuel Trim Index is greater than 20 percent? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S23163991262003062800000) .
3. Operate engine at idle. Using scan tool, observe the O2S parameters. Does scan tool indicate that the values are 200-800 mv and fluctuating? If yes, go to next step. If no, go to step 6 .
4. Turn engine off. Inspect the following items: Vacuum hoses for splits, kinks, and proper connections. If fuel pressure is too low, this DTC may set. Fuel contamination. Did you find and correct the condition? If yes, go to step 8 . If no, go to step 7 .
5. Turn engine off. Turn ignition on, with engine off. Observe the MAP sensor pressure parameter with scan tool. Refer to Altitude vs. Barometric Pressure table in «SENSOR OPERATING RANGE CHARTS - TRUCKS»(ref-159155) article. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP indicate the correct barometric pressure? If yes, go to next step. If no, go to «DTC P0105: MAP SENSOR CIRCUIT - INSUFFICIENT ACTIVITY»(ref-155898-S42645765212003062800000) .
6. Turn engine off. Inspect O2S for proper installation. Ensure electrical connectors and wires are secured and not contacting the exhaust system. Check for short between the signal circuit and low reference circuit. Did you find and correct the condition? If yes, go to step 8 . If no, diagnose fuel system. See «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Operate engine at idle. Check for missing, loose, or leaking exhaust components. Check for vacuum leaks at the intake manifold, throttle body, and injector "O" rings. Check the air induction system and air intake ducts for leaks. Check crankcase ventilation system for leaks. Did you find and correct the condition? If yes, go to next step. If no, see appropriate article in ENGINES.
8. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
9. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The system will go lean if an injector is not supplying enough fuel.
2. A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel.
3. Using scan tool, review the Failure Records. If an intermittent condition is suspected, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201, P0202, P0203, P0204, P0300, P0325, P0341, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, or P1441 not set.
2. Engine Coolant Temperature (ECT) is 140-239°F (60-115°C).
3. Intake air temperature is -13 to 239°F (-25 to 115°C).
4. Manifold Absolute Pressure (MAP) is more than 8.3 in. Hg (28 kPa).
5. Vehicle speed is less than 82 MPH.
6. Engine speed is 550-3600 RPM.
7. Barometric (BARO) pressure is more than 21.3 in. Hg (72 kPa).
8. The fuel ethanol composition is less than 88 percent.
9. Fuel level is more than 9.8 percent.

1. The fuel trim index is less than -35 percent.
2. Diagnostics have determined that a rich condition was not due to excessive vapor.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Install scan tool. Review the Freeze Frame/Failure Records and record displayed data for this DTC. Select Fuel Trim Data parameter. Start the engine and observe the Fuel Trim Index. Does scan tool indicate that the Fuel Trim Index is less than -35 percent? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S08045760402003062800000) .
3. Operate engine at idle. Observe O2S parameters with scan tool. Does scan tool indicate that the values are 200-800 mV and fluctuating? If yes, go to next step. If no, go to step 5 .
4. Turn engine off. Inspect the following items: Vacuum hoses for splits, kinks, and proper connections. The air intake duct for being collapsed or restricted. The air filter for being dirty or restricted. For objects blocking throttle body. Did you find and correct the condition? If yes, go to step 7 . If no, go to step 6 .
5. Turn engine off. Inspect the O2S for proper installation. Ensure electrical connectors and wires are secured and not contacting the exhaust system. Did you find and correct the condition? If yes, go to step 7 . If no, diagnose fuel system. See «BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-152692) article.
6. Inspect for the following conditions: Excessive fuel in the crankcase. Evaporative emissions control system. Fuel pressure regulator for proper operation. Ensure that all injectors are functioning properly. Perform the Fuel Injector Balance Test. Did you find and correct the condition? If yes, go to next step. If no, see appropriate article in ENGINES.
7. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
8. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. Fuel contamination, such as water and alcohol, will affect fuel trim.
2. System will go rich if injectors are supplying too much fuel.
3. Using scan tool, review the Failure Records. If an intermittent condition is suspected, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

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

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

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
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 DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S18643612352003062800000) .
3. Turn ignition off. Disconnect the fuel injector harness multi-way connector. Probe the appropriate fuel injector control circuit, PCM side, with a test light connected to battery voltage. Crank the engine. Does the test light flash when cranking the engine? If yes, go to step 7 . If no, go to next step.
4. Does the test light remain illuminated at all times? If yes, go to step 6 . If no, go to next step.
5. Test the control circuit of the fuel injector for a short to voltage or an open between the multi-way connector and the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
6. Test the control circuit of the fuel injector for a short to ground between the multi-way connector and the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
7. Inspect the accessible fuel injector jumper harness between the multi-way connector and the intake manifold for the following: Poor connections at the multi-way connector. Damaged or pinched wiring. Broken wires inside the insulation. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
8. Probe the appropriate fuel injector control circuit, fuel injector side, at the multi-way connector, with a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 15 . If no, go to next step.
9. With a DVOM, test for continuity between the ignition 1 voltage supply terminal and the appropriate fuel injector control circuit terminal, at the multi-way connector. Does the DVOM indicate OL? If yes, go to next step. If no, go to step 12 .
10. Test the control circuit of the fuel injector for an open or for poor connections at the fuel injector. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
11. Test the ignition 1 voltage supply circuit of the fuel injector for an open between the fuel injector and the splice. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
12. Test the control circuit of the fuel injector for a short to voltage or a short to another circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 16 .
13. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
14. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
15. Repair short to ground in the fuel injector control circuit. After repairs, go to step 18 .
16. Replace appropriate fuel injector. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 18 .
17. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
18. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
19. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. Performing the Fuel Injector Coil test may help isolate an intermittent condition. See «SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-153168) article.
2. For an intermittent condition, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. DTCs P0013, P0014, P0105, P0107, P0108, P0117, P0118, P0122, P0123, P0125, P0128, P0217, P0218, P0336, P0340, P0341, P0365, P0366, P0502, P0503, P1114, P1115, P1121, P1122, P1336, or P1345 not set.
2. Engine is running.
3. System voltage is 10-18 volts.
4. Engine Coolant Temperature (ECT) is 19-266°F (7-130°C).
5. Throttle angle is steady.
6. A/C compressor clutch is not changing state.
7. Exhaust Gas Recirculation (EGR) flow test is inactive.
8. Fuel level is more than 10 percent.
9. The fuel cut-off or Decel Fuel Cut-Off (DFCO) mode is not active.
10. PCM is not receiving a rough road signal.

1. PCM determines that an emission type misfire is present on more than one cylinder.
2. PCM determines that a catalyst damaging misfire is present.

1. If the misfire level is non-catalyst damaging, the PCM will illuminate the MIL during the second key cycle in which the DTC sets.
2. If the misfire is severe enough to cause possible catalyst damage, the PCM will immediately flash the MIL while the misfire remains at catalyst damaging levels.
3. The PCM will disable the Torque Converter Clutch (TCC) operation.
4. The PCM will store the conditions present when the DTC set as Freeze Frame/Failure Records data. Any data previously stored in Freeze Frame will be overwritten when this DTC sets. The only exception to this is if a fuel trim DTC was already recorded in Freeze Frame. In this case, the fuel trim data stays in Freeze Frame and the Misfire Data will be stored in Failure Records.

1. The PCM will turn the MIL OFF after 3 consecutive trips during which the diagnostic runs and passes. Note that if the last failure was during a non-typical driving condition, the MIL may remain ON longer than 3 drive trips. Review Freeze Frame for the last failure conditions.
2. The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool Clear DTC Information function.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start and allow engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. Monitor all of the Misfire counters with the scan tool. Are any of the Misfire current counters incrementing? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S29559372762003062800000) .
3. Are any other DTCs set? If yes, diagnose affected DTC(s) first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
4. Can any abnormal engine noise be heard? If yes, diagnose engine mechanical condition. If no, go to next step.
5. Inspect vacuum hoses and seals for splits, restrictions, and improper connections. Check throttle body and intake manifold for vacuum leaks, crankcase ventilation system for vacuum leaks, PCM grounds for corrosion and loose connections, exhaust system for restrictions, or for fuel contamination. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 8 .
6. Turn ignition off. Remove the fuel pump relay. Remove an ignition coil that corresponds to the Misfire Current counters that were incrementing. Connect the ignition coil connector to the ignition coil. Connect a jumper wire between the ignition coil and a good ground. Install Spark Tester (J-26792) on the ignition coil and a good ground. Crank engine. Repeat the steps by installing the spark tester on the other affected cylinders. Does the spark tester spark on all the affected cylinders? If yes, go to step 8 . If no, go to next step.
7. Inspect the affected cylinder spark plug boot for a missing or damaged ignition coil spring. Did you find and correct the condition? If yes, go to step 17 . If no, diagnose Electronic Ignition (EI) System. See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(ref-153168-S18519169542003032100000) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
8. Remove spark plug from the cylinder that indicated a misfire. Inspect the spark plug. Does the spark plug appear to be okay? If yes, go to next step. If no, go to step 10 .
9. Exchange the suspected spark plug with another cylinder that is operating properly. Operate the vehicle under the same conditions that the misfire occurred. Did the misfire move with the spark plug? If yes, go to step 16 . If no, go to step 13 .
10. Is the spark plug oil or coolant fouled? If yes, diagnose for an engine mechanical condition. If spark plug is okay, go to next step.
11. Is the spark plug gas fouled? If yes, go to step 14 . If no, go to next step.
12. Did the spark plug show any signs of being cracked, worn, or improperly gapped? If yes, go to step 15 . If no, go to next step.
13. Perform the fuel injector coil test. Did you find and correct the condition? If yes, go to step 17 . If no, diagnose for an engine mechanical problem.
14. Perform fuel system diagnosis. Did you find and correct the condition? If yes, go to step 17 . If no, diagnose for an engine mechanical problem.
15. Replace or gap the spark plug. After repairs, go to step 17 .
16. Replace the faulty spark plug. After replacing spark plugs, go to next step
17. Operate the vehicle at 2500 RPM for 4 minutes. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S41959280532003062800000) . Does the DTC run and pass? If yes, go to step 19 . If no, go to «DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)»(ref-155898-S00120696492003062800000) .
18. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
19. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S41959280532003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
20. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Check for the following conditions

1. Incorrect CKP system variation data stored in the PCM. Run the CKP System Variation Learn Procedure using scan tool. See «CRANKSHAFT POSITION SENSOR»(ref-155898-S34895643712003062800000) under PROGRAMMING.
2. System grounds. Ensure that all connections are clean and properly tightened.
3. Damaged accessory drive belt or driven accessory. A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.
4. Fuel pressure. Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. See «BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-152692) article.
5. Fuel injectors. See «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.3L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
6. Contaminated fuel.
7. Extended idle. Excessive Open Loop operation caused by extended idling or short trip driving may leave deposits on the Heated Oxygen Sensors (HO2S). The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the Freeze Frame/Failure Records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures less than 176°F (80°C), the condition described is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows more than 15 g/s.
8. Running the vehicle low on fuel. This DTC may set if the vehicle misfires while running out of fuel. If no misfire is currently present, but the History Counters indicate random misfire was once present, ask if the vehicle has been run out of fuel. If this is the case, no further repair may be necessary.

Note. If the level of misfire was sufficient to cause possible catalyst damage, if the MIL was flashing, ensure that the DTC P0420 test is completed and passed after verifying the misfire repair. See DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1) .

If the condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. DTC P0013, P0014, P0105, P0107, P0108, P0117, P0118, P0122, P0123, P0125, P0128, P0217, P0218, P0336, P0340, P0341, P0365, P0366, P0502, P0503, P1114, P1115, P1120, P1220, P1221, P1336, or P1345 not set.
2. Engine speed is 450-5000 RPM.
3. Ignition voltage is 10-18 volts.
4. Engine Coolant Temperature (ECT) is 19-266°F ( -7 and 130°C).
5. Fuel level is more than 10 percent.
6. Throttle angle is steady within one percent.
7. Anti-lock Brake System (ABS) is not active.
8. Transmission is not changing gears.
9. A/C clutch is not changing states.
10. PCM is not in fuel shut-off or decel fuel cut-off mode.
11. PCM is not receiving a rough road signal.

1. The PCM determines that an emission type misfire is present.
2. The PCM determines that a catalyst damaging misfire is present.

1. If the misfire level is non-catalyst damaging, the PCM will illuminate the MIL during the second key cycle in which the DTC sets.
2. If the misfire is severe enough to cause possible catalyst damage, the PCM will immediately flash the MIL while the misfire remains at catalyst damaging levels.
3. The PCM will disable the Torque Converter Clutch (TCC) operation.
4. The PCM will store the conditions present when the DTC set as Freeze Frame/Failure Records data. Any data previously stored in Freeze Frame will be overwritten when this DTC sets. The only exception to this is if a fuel trim DTC was already recorded in Freeze Frame. In this case, the fuel trim data stays in Freeze Frame and the Misfire Data will be stored in Failure Records.

1. The PCM will turn the MIL OFF after 3 consecutive trips during which the diagnostic runs and passes. Note that if the last failure was during a non-typical driving condition, the MIL may remain ON longer than 3 drive trips. Review Freeze Frame for the last failure conditions.
2. The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool Clear DTC Information function.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start engine. Allow engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. Monitor all of the Misfire counters with the scan tool. Are any of the Misfire current counters incrementing? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Are any other DTCs set? If yes, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
4. Can any abnormal engine noise be heard? If yes, diagnose engine mechanical condition. If no, go to next step.
5. Turn ignition off. Remove the fuel pump relay. Remove the ignition coil for the affected cylinder, keeping the ignition connected to the harness connector. Connect a jumper wire between the ignition coil and a good ground. Install Spark Tester (J-26792) on the ignition coil and a good ground. Crank engine. Does the spark tester spark? If yes, go to step 7 . If no, go to next step.
6. Inspect the affected cylinder spark plug boot for a missing or damaged ignition coil spring. Did you find and correct the condition? If yes, go to step 15 . If no, diagnose Electronic Ignition (EI) System. See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(ref-153168-S18519169542003032100000) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Remove the spark plug from the cylinder that indicated a misfire. Inspect the spark plug. Does the spark plug appear to be okay? If yes, go to next step. If no, go to step 9 .
8. Exchange the suspected spark plug with another cylinder that is operating properly. Operate the vehicle under the same conditions that the misfire occurred. Did the misfire move with the spark plug? If yes, go to step 14 . If no, go to step 12 .
9. Is the spark plug oil or coolant fouled? If yes, diagnose for an engine mechanical problem. If no, go to next step.
10. Is the spark plug gas fouled? If yes, go to step 12 . If no, go to next step.
11. Did the spark plug show any signs of being cracked, worn, or improperly gapped? If yes, go to step 13 . If no, go to next step.
12. Perform the fuel injector coil test. Did you find and correct the condition? If yes, go to step 15 . If no, diagnose for an engine mechanical condition.
13. Replace or gap the spark plug. After repairs, go to step 15 .
14. Replace faulty spark plug. After replacing spark plug, go to next step.
15. Was the customer's concerned about the MIL flashing? If yes, go to next step. If no, go to step 17 .
16. Operate the vehicle at 2500 RPM for 4 minutes. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S22532392002003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to «DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)»(ref-155898-S00120696492003062800000) .
17. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S25123313802003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
18. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0117, P0118, P0122, P0123, P0327, or P0332 not set.
2. Engine run time is more than 20 seconds.
3. Engine Coolant Temperature (ECT) is more than 158°F (70°C).
4. Engine speed is 2000-6400 RPM.
5. Manifold Absolute Pressure (MAP) is more than 18 in. Hg (60 kPa).

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

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
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 DTC or as close as possible to the Freeze Frame/Failure Records data that you observed. Did the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
4. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
5. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0117, P0118, P0122, or P0123 not set.
2. The ignition voltage is more than 10 volts.
3. Engine Coolant Temperature (ECT) sensor is more than 158°F (70°C).
4. Engine run time is more than 20 seconds.
5. Manifold Absolute Pressure (MAP) is more than 18 in. Hg (60 kPa).
6. Engine speed is 2000-6400 RPM.

The knock sensor signal is outside the normal operating range or the knock sensor signal is not present.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Observe the Freeze Frame/Failure Records data for this DTC. Turn the ignition OFF for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Turn ignition off. Disconnect the affected KS. Set the DVOM to the ohms scale. Measure the resistance from the signal terminal on the KS to a good ground with the DVOM. Measure the resistance from the low reference terminal on the KS to a good ground with the DVOM. Does the DVOM display OL for both terminals? If yes, go to next step. If no, go to step 10 .
4. Connect the DVOM between the terminals of the affected KS. Set the DVOM to the 400 mV AC hertz scale and wait for the DVOM to stabilize at zero Hz. DO NOT tap on plastic engine components. Tap on the engine block with a non-metallic object near the affected KS while observing the signal indicated on the DVOM. Does the DVOM display a fluctuating frequency while tapping on the engine block? If yes, go to next step. If no, go to step 10 .
5. Turn ignition on, with engine off. Measure the voltage at the KS signal circuit to a good ground with a DVOM. Measure the voltage at the KS low reference circuit to a good ground with a DVOM. Does the DVOM display a voltage greater than one volt on either circuit? If yes, go to next step. If no, go to step 7 .
6. Turn ignition off Disconnect the PCM. Test the KS signal circuit or the KS low reference circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
7. Turn ignition off. Disconnect the PCM. Test the KS signal circuit and the KS low reference circuit for an open, for a high resistance, and for a short to ground. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 9 .
8. Test for an intermittent and for a poor connection at the affected KS. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 12 . If no, go to step 11 .
10. Replace knock sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 12 .
11. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
12. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
13. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The knock sensor must be correctly tightened to 18 ft. lbs. (25 N.m).
2. The mounting between the sensor and engine must be free of burrs, casting flash, and foreign material.
3. The knock sensor head is clear from hoses, brackets, and engine wiring.
4. If knock sensor is dropped, it must be replaced.
5. For an intermittent condition, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. The engine is running.
2. Battery voltage is less than 18 volts.
3. DTC P0562 is not set.

PCM detects there is no signal from the CKP sensor.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start engine. Observe the CKP active counter on scan tool. Does the CKP active counter increment? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S18898096182003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the PCM connector. Measure the resistance from the CKP sensor signal circuit to the low reference circuit of the CKP sensor with a DVOM. Is the resistance 500-1000 ohms? If yes, go to next step. If no, go to step 6 .
5. Test the CKP sensor circuits for a short to voltage or a short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 9 .
6. Test the CKP sensor circuits for an open, short across circuit, or high resistance. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
7. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
8. Test for an intermittent and for a poor connection at the CKP sensor. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
9. Test for shorted terminals and poor connections at the PCM. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
10. Remove the CKP sensor. Visually inspect the CKP sensor for foreign material passing between the CKP sensor and reluctor wheel, physical damage, excessive air gap between CKP sensor and reluctor wheel, loose or improper installation, electromagnetic interference in the CKP sensor circuits, or wiring routed too closely to secondary ignition components. Did you find and correct the conditions? If yes, go to step 14 . If no, go to next step.
11. Visually inspect the CKP reluctor wheel for physical damage, incorrect installation, or excessive end play or looseness. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
12. Replace CKP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to 14 .
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S18898096182003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The engine is running.
2. DTCs P0340 or P0341 not set.

The CKP resync counter goes more than 15 times within 4 minutes and 15 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Attempt to start the engine. Will the engine start? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S28405989682003062800000) .
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 DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC failed this ignition? If yes, go to next step. If no, go to step 5 .
4. With the engine running, wiggle the electrical connectors of the following components and related circuits while listening for the engine to stumble: The PCM The CKP sensor Does the engine stumble? If yes, go to step 6 . If no, go to step 7 .
5. Operate any non-engine related electronic component on the vehicle. Observe the Med. Resolution Resync Counter with scan tool. Does the Med. Resolution Resync Counter on scan tool increment while operating any non-engine related electronic components? If yes, go to step 9 . If no, go to step 14 .
6. Turn ignition off. Repair intermittent and a poor connection that caused the engine to stumble. After repairs, go to step 14 .
7. Did the MIL illuminate in step 3 ? If yes, go to next step. If no, go to step 14 .
8. Turn ignition off. Check the following items for rubbed-through wire insulation or for wiring being pinched: The PCM. The CKP sensor. Repair wiring as necessary. After repairs, go to step 14 . If no problem was found, go to step 10 .
9. Turn ignition off. Repair circuitry of the malfunctioning or interfering component. Move any wiring that is causing the interference away from the CKP sensor and ICM wiring harness. After repairs, go to step 14 .
10. Remove CKP sensor. Visually inspect the CKP sensor for any physical damage, loose or improper installation, or wiring routed too closely to secondary ignition components. Did you find and correct the condition? If yes, go to next step. If no, go to step 14 .
11. Visually inspect the CKP sensor reluctor wheel for damage or looseness. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
12. Replace CKP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Idle the engine for 5 minutes or until the Malfunction Indicator Light (MIL) turns ON. Did the MIL illuminate? If yes, go to next step. If no, go to step 14 .
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S20931796292003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. If the DTC is determined to be intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
2. An intermittent can also be the result of a defective reluctor wheel. Remove the crankshaft position sensor and inspect the reluctor wheel through the hole.

The engine is running.

The CMP Active Counter is not incrementing.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
2. The PCM records the operating conditions at the time when the diagnostic fails. This information stores in the Freeze Frame and Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool to clear the DTCs

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Start and idle engine. Use scan tool in order to monitor the CMP active counter. Does scan tool indicate the CMP active counter is incrementing? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observe. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S31938064382003062800000) . Does the DTC reset? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S38048646852003062800000) .
4. Turn ignition off. Disconnect the CMP sensor. Turn ignition on, with engine off. Probe the 12-volt reference circuit with a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 7 .
5. Turn ignition off. Jumper the CMP circuits from the CMP sensor to the CMP sensor harness connector. Turn ignition on, with engine off. Measure the voltage drop from the low reference circuit of the CMP sensor to a good ground with a DVOM. Is the voltage more than 0.2 volt? If yes, go to step 8 . If no, go to next step.
6. Leave the jumper wires installed. Remove the jumper wire from the CMP sensor signal circuit on the PCM side. Start the engine. Measure the duty cycle from the CMP sensor signal circuit on the sensor side and to a good ground with a DVOM. Is the duty cycle within 40-50 percent? If yes, go to step 9 . If no, go to step 10 .
7. Test the 12-volt reference circuit for an open, high resistance or a short to ground. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 11 .
8. Test the low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 11 .
9. Test the signal circuit for an open, short to ground or a short to voltage. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 11 .
10. Test for an intermittent and for a poor connection at the CMP sensor. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 12 .
11. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
12. Remove the CMP sensor. Visually inspect the CMP sensor for physical damage, loose or improper installation. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
13. Replace CMP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 16 .
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S31938064382003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
16. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. Whenever the PCM sees less than 15 resyncs in 256 seconds, the counter resets to zero. When a poor connection is present, the cam sensor active counter stops incrementing and the cam sensor resync counter starts to increment.
2. Inspect the wiring harness for damage. If the harness appears to be okay, observe the CMP resync counter on scan tool while moving connectors and wiring harnesses related to the CMP sensor. If the CMP resync counter still does not count, then while still observing scan tool, operate any non-engine related electrical components on the vehicle. A change in display will indicate the location of the malfunction.
3. A defective reluctor wheel or a cracked or damaged CMP sensor can result in an intermittent. Remove the camshaft position sensor and inspect for any damage. With the CMP sensor removed you can also inspect the reluctor wheel through the hole. Check the porosity and condition of the wheel. The edges must be square. Look for a nicked or damaged wheel.
4. If the DTC is determined to be intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

The engine is running.

The PCM sees more than 15 CMP sensor resyncs in 256 seconds (4 minutes 16 seconds).

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm up cycles without a fault.
3. Scan tool can clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. Connect scan tool. Are any other DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
3. Start engine. Observe the CMP Resync Counter with scan tool. Is the CMP Resync Counter incrementing? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S39139454802003062800000) .
4. Turn ignition off. Disconnect the CMP sensor electrical connector. Start the engine. Observe CMP Resync on scan tool. Did the CMP Resync Counter stop incrementing? If yes, go to next step. If no, go to step 6 .
5. Turn engine off. With the CMP sensor connector still disconnected, connect a DVOM set to the DC HZ scale from the CMP sensor signal circuit (PCM side) to ground. Start and idle the engine. Does the DVOM display a Hertz reading more than zero Hz? If yes, go to next step. If no, go to step 7 .
6. Visually and physically inspect all circuits going to the CMP sensor for the following: Being routed too close to secondary ignition wires or components. Being routed too close to aftermarket add-on electrical equipment. Being routed too close to solenoids, relays, and motors. If you find incorrect routing, correct the harness routing. Did you find and correct the condition? Inspect the CMP sensor harness for incorrect routing or shorted to another circuit that generates frequency: Did you locate and correct the condition? If yes, go to step 11 . If no, go to step 9 .
7. Turn ignition off. Check for a faulty electrical connection at the CMP sensor electrical connector. Repair electrical connector as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
8. Replace Camshaft Position (CMP) sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 11 .
9. Disconnect the PCM electrical connector. Check the PCM terminals for a faulty electrical connection. Repair terminals as necessary. Did you find and correct the condition? If problem was found, go to step 11 . If problem was not found, go to next step.
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S13076939702003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. If the PCM sees less than 15 resyncs in 256 seconds, the counter is reset to zero. When a faulty electrical connection is present, the CMP Reference Activity counter will stop incrementing and the CMP Resync Counter will increment.
2. If the DTC is determined to be intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. DTCs P0013, P0014, P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0301-P0306, P0326, P0327, P0332, P0336, P0340, P0341, P0440, P0442, P0446, P0452, P0453, P0502, P0503, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1133, P1220, P1221, P1271, P1275, P1280, P1441, P1512, P1514, P1515, P1516, P1635, or P1639 not set.
2. Engine speed is more than 1000 RPM for a minimum of 36 seconds since the end of the last idle period.
3. Barometric (BARO) pressure is more than 21.3 in. Hg (72 kPa).
4. Intake Air Temperature (IAT) is -5 to 176°F (-20.5 to 80.0°C).
5. Engine Coolant Temperature (ECT) is 158-257°F (70-125°C).
6. Battery voltage is more than 9 volts.
7. The calculated air flow is less than 15 g/sec.
8. Engine run time is more than 530 seconds.
9. Vehicle speed is less than 3 MPH.
10. Tests attempted this trip are less than 12.
11. Predicted catalyst temperature is 934-1382°F (501-750°C).

The PCM determines that the oxygen storage capacity of the converter is degraded past a calibrated value.

1. The control module illuminates the Malfunction Indicator Light (MIL) the first time the diagnostic runs and fails.
2. The control module will set the DTC and records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

1. The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
2. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 40°F (22°C) from the start-up coolant temperature and the engine coolant reaches a temperature that is more than 158°F (70°C) during the same ignition cycle.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start and operate engine at idle until Closed Loop is achieved. Increase engine speed to 1500 RPM. Monitor the HO2S 1 and 2 voltage parameters on scan tool. Is the HO2S 2 voltage parameter as active as the HO2S 1 voltage parameter? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze/Frame Records for this DTC. Clear the DTCs with a scan tool. Turn the OFF all accessories. Operate the vehicle within the Conditions For Running this DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S22532392002003062800000) . The test may need to be completed up to 6 times in order to pass or fail. If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle, the test may be aborting. Does the scan tool indicate DTC P0420 ran and passed this ignition? If yes, go to «DIAGNOSTIC AIDS»(ref-155898-S05857835322003062800000) . If no, go to next step.
4. Visually and physically inspect the catalytic converter for dents, severe discoloration caused by excessive temperatures, road damage, internal rattle caused by damaged catalyst substrate, or restrictions. Did you find a condition? If yes, go to step 8 . If no, go to next step.
5. Visually inspect the exhaust system for leaks, physical damage, loose or missing hardware, or HO2S 2 for proper torque. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
6. Visually inspect the HO2S 2 pigtail and wiring harness contacting the exhaust or a ground. Inspect for physical damage. Did you find a condition? If yes, go to next step. If no, go to step 8 .
7. Replace HO2S 2 sensor. After replacing sensor, go to step 9 .
8. Replace catalytic converter. After replacing converter, go to next step.
9. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S22532392002003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
10. Observe the Capture Info with a scan tool. Are there any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Fuel with a high sulfur or lead content can degrade marginal converter's performance. Be sure to check the fuel quality.

An intermittent may be caused by any of the following conditions

1. A poor connection.
2. Rubbed-through wire insulation.
3. A broken wire inside the insulation.

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Repair circuits as necessary.

1. DTC P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0125, P0452, or P0453 not set.
2. Ignition voltage is 10-18 volts.
3. Barometric (BARO) pressure is more than 22 in. Hg (75 kPa).
4. Fuel level is 15-85 percent.
5. Engine Coolant Temperature (ECT) is 39-86°F (4-30°C).
6. Intake Air Temperature (IAT) is 39-86°F (4-30°C).
7. Start-up ECT and IAT are within 16°F (9°C) of each other.
8. Vehicle Speed Sensor (VSS) is less than 75 MPH.

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

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Inspect the EVAP system for a loose, missing, or damaged service port Schrader valve, loose, incorrect, missing, or damaged fuel fill cap, or damaged EVAP purge solenoid. Raise and support vehicle on a hoist. Inspect the EVAP system for any disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses, damaged EVAP vent solenoid or EVAP canister. Did you find and correct the condition? If yes, go to step 34 . If no, go to next step.
3. Clear the DTCs with a scan tool. Command the EVAP purge solenoid to 50 percent and back to zero percent with scan tool. Do you hear or feel a clicking from the EVAP purge solenoid when it is commanded to 50 percent? If yes, go to next step. If no, go to step 5 .
4. Command the EVAP vent solenoid ON and OFF with scan tool. Do you hear or feel a click as the EVAP vent solenoid is commanded ON and OFF? If yes, go to step 9 . If no, go to step 7 .
5. Disconnect the EVAP purge solenoid. Turn ignition on, with engine off. Connect a test light between the ignition 1 voltage circuit of the EVAP purge solenoid and a known-good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 25 .
6. Connect a test light between the ignition 1 voltage circuit of the EVAP purge solenoid and the control circuit of the EVAP purge solenoid. Command the EVAP purge solenoid to 50 percent and then to zero percent with scan tool. Does the test light illuminate or pulsate when the EVAP purge solenoid is commanded to 50 percent and turn OFF when the EVAP purge solenoid is commanded to zero percent? If yes, go to step 20 . If no, go to step 18 .
7. Turn ignition on, with engine off. Disconnect the EVAP vent solenoid. Connect a test light between the ignition 1 voltage circuit of the EVAP vent solenoid and a known-good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 26 .
8. Connect a test light between the ignition 1 voltage circuit of the EVAP vent solenoid and the control circuit of the EVAP vent solenoid. Command the EVAP vent solenoid ON, with scan tool. Does the test light illuminate? If yes, go to step 21 . If no, go to step 19 .
9. Turn ignition off. Connect Evaporative Emissions System Tester (J-41413-200) power supply clips to a known-good 12-volt source. Install the Fuel Tank Cap Adapter (J-41415-40) to fuel fill pipe. Connect fuel fill cap to the Fuel Tank Cap Adapter. Connect the nitrogen/smoke supply hose from the Evaporative Emissions System Tester to the Fuel Tank Cap Adapter. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Turn the nitrogen/smoke valve on the control panel to SMOKE. Use the remote switch to introduce smoke into the EVAP system. Use the EVAP Service Port Vent Fitting (J-41413-VLV) to open the EVAP service port. Remove the EVAP Service Port Vent Fitting once smoke is observed. Continue to introduce smoke into the EVAP system for an additional 60 seconds. Inspect the entire EVAP system for exiting smoke with the High Intensity White Light (J-41413-SPT). Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step 34 . If no, go to next step.
10. Disconnect the Fuel Tank Cap Adapter (J-41415-40) from the fuel fill pipe. Install fuel fill cap to fuel fill pipe. Connect the nitrogen/smoke supply hose to the EVAP service port. Use the remote switch to introduce smoke into the EVAP system. Inspect the entire EVAP system for exiting smoke with the High Intensity White Light (J-41413-SPT). Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step 34 . If no, go to next step.
11. Use the remote switch to stop introducing smoke. Install the Fuel Tank Cap Adapter (J-41415-40) to the fuel fill pipe. Connect the nitrogen/smoke supply hose to the Fuel Tank Cap Adapter. Connect fuel fill cap to the Fuel Tank Cap Adapter. Command the EVAP vent solenoid open with scan tool. Compare the Fuel Tank Pressure Sensor parameter with a scan tool, to the Pressure/Vacuum Gauge (J-41413-200). Is the scan tool Fuel Tank Pressure Sensor parameter within 1 in. H2O of the pressure/vacuum gauge? If yes, go to next step. If no, go to step 22 .
12. Seal the EVAP system using the EVAP Purge/Seal function on scan tool. Turn the nitrogen/smoke valve on the Evaporative Emissions System Tester control panel to NITROGEN. Use the Evaporative Emissions System Tester to pressurize the EVAP system to 10 in. H2O. Is the Fuel Tank Pressure Sensor parameter more than the 5 in. H2O? If yes, go to next step. If no, go to step 22 .
13. Use the remote switch to stop introducing nitrogen into the EVAP system. Increase the EVAP purge solenoid to 100 percent. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to «DIAGNOSTIC AIDS»(ref-155898-S23980490262003062800000) . If no, go to next step.
14. Disconnect the EVAP purge vacuum source from the EVAP purge solenoid. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step 24 . If no, go to next step.
15. Disconnect the EVAP purge pipe from the EVAP purge solenoid. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step 29 . If no, go to next step.
16. Disconnect the EVAP purge pipe at the EVAP canister. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step 27 . If no, go to next step.
17. Disconnect the EVAP vapor pipe at the EVAP canister. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step 31 . If no, go to step 28 .
18. Test the control circuit of the EVAP purge solenoid for an open or for a short to voltage. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 23 .
19. Test the control circuit of the EVAP vent solenoid for an open or for a short to voltage. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 23 .
20. Test for an intermittent and for a poor connection at the EVAP canister purge solenoid. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 29 .
21. Test for an intermittent and for a poor connection at the EVAP vent solenoid. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 30 .
22. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 32 .
23. Test for an intermittent and for a poor connection at the control module. Did you find and correct the condition? If yes, go to step 34 . If no, go to step 33 .
24. Repair pinched or obstructed EVAP purge solenoid vacuum source. After repairs, go to step 34 .
25. Repair open or short to ground in the ignition 1 voltage circuit of the EVAP purge solenoid. Replace fuse as necessary. After repairs, go to step 34 .
26. Repair open or short to ground in the ignition 1 voltage circuit of the EVAP vent solenoid. Replace fuse as necessary. After repairs, go to step 34 .
27. Repair restriction in the EVAP purge pipe. After repairs, go to step 34 .
28. Repair restriction in the EVAP vapor pipe. After repairs, go to step 34
29. Replace EVAP purge solenoid. After replacing solenoid, go to step 34 .
30. Replace EVAP vent solenoid. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing solenoid, go to step 34 .
31. Replace EVAP canister. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing EVAP canister, go to step 34 .
32. Replace FTP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 34 .
33. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
34. Connect the Pressure/Vacuum Gauge (J-41413-200) to fuel fill pipe. Turn the nitrogen/smoke valve to NITROGEN. Seal the EVAP system using the EVAP purge/seal function on scan tool. Pressurize the EVAP system to 5 in. H2O. Observe the pressure/vacuum gauge for 5 minutes. Does the pressure/vacuum gauge remain constant? If yes, go to next step. If no, go to step 2 .
35. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

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

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0452, or P0453 not set.
2. Ignition voltage is 10-18 volts.
3. Barometric (BARO) pressure is more than 22 in. Hg (75 kPa).
4. Fuel level is 15-85 percent.
5. Engine Coolant Temperature (ECT) is 39-86°F (4-30°C).
6. Intake Air Temperature (IAT) is 39-86°F (4-30°C).
7. The start-up ECT and IAT are within 16°F (9°C) of each other.
8. Vehicle Speed Sensor (VSS) is less than 75 MPH (121 km/h).

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

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Inspect the EVAP system for the following conditions: A loose, incorrect, faulty, or missing fuel tank fill cap. Damaged or disconnected EVAP system purge lines. A damaged EVAP system component. A loose, missing, or damaged service port Schrader valve. Did you find and correct the condition? If yes, go to step 5 . If no, go to next step.
3. Turn ignition off. Connect the Evaporative Emissions System Tester (J-41413-200) power supply clips to a known-good 12-volt source. Install the Fuel Tank Cap Adapter (J-41415-40) to the fuel fill pipe. Connect the fuel fill cap to the Fuel Tank Cap Adapter. Connect the Evaporative Emissions System Tester nitrogen/smoke supply hose to the Fuel Tank Cap Adapter. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Turn the nitrogen/smoke valve on the Evaporative Emissions System Tester control panel to SMOKE. Use the remote switch to introduce smoke into the EVAP system. Use the EVAP Service Port Vent Fitting (J-41413-VLV) to open the EVAP service port. Remove the EVAP Service Port Vent Fitting once smoke is observed. Continue to introduce smoke into the EVAP system for an additional 60 seconds. Inspect the entire EVAP system for exiting smoke with the High Intensity White Light (J-41413-SPT). Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to step 5 . If no, go to next step.
4. Disconnect the Fuel Tank Cap Adapter from the fuel fill pipe. Install the fuel fill cap to the fuel fill pipe. Connect the Evaporative Emissions System Tester nitrogen/smoke supply hose to the EVAP service port. Use the remote switch to introduce smoke into the EVAP system. Inspect the entire EVAP system for exiting smoke with the High Intensity White Light (J-41413-PT). Continue to introduce smoke at 15 second intervals until the leak source has been located. Did you locate and repair a leak source? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S09109926502003062800000) .
5. Turn the nitrogen/smoke valve to nitrogen. Connect the nitrogen/smoke hose to the 0.20" (0.5 mm) test orifice on the bottom front of the Evaporative Emissions System Tester. Use the remote switch to activate the Evaporative Emissions System Tester. Align the Red flag on the flow meter with the floating indicator. Use the remote switch to de-activate the Evaporative Emissions System Tester. Install the Fuel Tank Cap Adapter to the fuel fill pipe. Remove the nitrogen/smoke hose from the test orifice and install the hose onto the Fuel Tank Cap Adapter. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Use the remote switch to introduce nitrogen and fill the EVAP system until the floating stabilizes. Compare the flow meter's stable floating indicator position to the Red flag. Is the floating indicator below the Red flag? If yes, go to next step. If no, go to step 2 .
6. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Note. If carbon release is detected, see EVAPORATIVE EMISSION SYSTEM CLEANING in REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT .

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

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

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0452, or P0453 not set.
2. The ignition voltage is 10-18 volts.
3. Barometric (BARO) pressure is more than 22 in. Hg (75 kPa).
4. Fuel level is 15-85 percent.
5. Engine Coolant Temperature (ECT) is 39-86°F (4-30°C).
6. Intake Air Temperature (IAT) is 39-86°F (4-30°C).
7. The start-up ECT and IAT are within 16°F (9°C) of each other.
8. Vehicle Speed Sensor (VSS) is less than 75 MPH.

1. The Fuel Tank Pressure (FTP) is less than -10 in. H2O.
2. Condition is present for at least 30 seconds.

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

1. The PCM will turn OFF the MIL during the first trip in which the diagnostic has been run and passed.
2. The history DTC will clear when the PCM turns OFF the MIL.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Inspect the EVAP system for damaged EVAP vent solenoid, pinched EVAP vent hose, or damaged EVAP canister. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
3. Turn ignition off. Disconnect the EVAP purge line from the EVAP purge solenoid. Turn ignition on, with engine off. Is the Fuel Tank Pressure Sensor parameter within -1 to 1 in. H20? If yes, go to next step. If no, go to step 10 .
4. Turn ignition off. Connect the EVAP purge pipe. Connect the Evaporative Emissions System Tester (J-41413-200) power supply clips to a known-good 12-volt source. Install the Fuel Fill Cap Adapter (J-41415-40) to the fuel fill pipe. Connect the fuel fill cap to the Fuel Fill Cap Adapter. Connect the Evaporative Emissions System Tester nitrogen/smoke supply hose to the Fuel Fill Cap Adapter. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Turn the nitrogen/smoke valve on the Evaporative Emissions System Tester control panel to NITROGEN. Use the remote switch to pressurize the EVAP system to 5 in. H2O. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Command the EVAP vent solenoid open with scan tool. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to «DIAGNOSTIC AIDS»(ref-155898-S33308107752003062800000) . If no, go to next step.
5. Command the EVAP vent solenoid ON and OFF with a scan tool. Do you hear or feel the EVAP vent solenoid click when commanded ON and OFF? If yes, go to next step. If no, go to step 8 .
6. Disconnect the EVAP vent hose from the EVAP vent solenoid. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step 12 . If no, go to next step.
7. Disconnect the EVAP vent hose from the EVAP canister. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step 14 . If no, go to step 13 .
8. Disconnect the EVAP vent solenoid. Probe the control circuit of the EVAP vent solenoid with a test light that is connected to battery voltage. Does the test light illuminate? If yes, go to next step. If no, go to step 12 .
9. Test the EVAP vent solenoid control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 11 .
10. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 15 .
11. Test for an intermittent and for a poor connection at the control module. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 16 .
12. Replace EVAP vent solenoid. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing solenoid, go to step 17 .
13. Replace EVAP canister. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing EVAP canister, go to step 17 .
14. Repair blockage in the EVAP vent hose. After repairs, go to step 17 .
15. Replace FTP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 17 .
16. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
17. Turn ignition off. Connect all disconnected components. Connect the Evaporative Emissions System Tester to the fuel fill pipe. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Turn the nitrogen/smoke valve on the Evaporative Emissions System Tester control panel to NITROGEN. Use the remote switch to pressurize the EVAP system to 5 in. H2O. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Command the EVAP vent solenoid open with a scan tool. Is the Fuel Tank Pressure Sensor parameter less than zero in. H2O? If yes, go to next step. If no, go to step 2 .
18. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The EVAP system tests run when the engine is first started and meets the Conditions For Running DTC. An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem. Repair blockage in the EVAP system.

Ignition is on.

1. The fuel tank pressure sensor voltage is less than 0.1 volt.
2. Conditions present for greater than 5 seconds.

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

1. PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic ran and passed.
2. The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. With scan tool, observe the Fuel Tank Pressure (FTP) sensor voltage. Does scan tool indicate that the FTP sensor voltage is less than 0.1 volt? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S15012607872003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition on, with engine off. Disconnect the FTP sensor. Measure the voltage from the 5-volt reference circuit of the FTP sensor to a good ground with a DVOM. Is the voltage within 4.8-5.2 volts? If yes, go to step 6 . If no, go to next step.
5. Disconnect the following components, while monitoring the DVOM: MAP sensor, TP sensor and A/C pressure sensor. Is DVOM reading within 4.8-5.2 volts when any of the components are disconnected? If yes, go to step 11 . If no, go to step 7 .
6. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the FTP sensor and the signal circuit of the FTP sensor. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Is Fuel Tank Pressure Sensor parameter within 4.8-5.2 volts? If yes, go to step 9 . If no, go to step 8 .
7. Test the FTP 5-volt reference circuit for an open or for a short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
8. Test the FTP sensor signal circuit for an open or for a short to ground. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 10 .
9. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
10. Test for an intermittent and for a poor connection at the control module. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
11. Replace the component that affected the 5-volt reference circuit. After replacing component(s), go to step 14 .
12. Replace FTP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 14 .
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S15012607872003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The ignition is on.

1. Fuel tank pressure sensor voltage is more than 4.9 volts.
2. Condition present for greater than 5 seconds.

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

1. PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic ran and passed.
2. The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition off. Remove fuel cap. Turn ignition on, with engine off. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Is the Fuel Tank Pressure Sensor parameter more than 4.3 volts? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Turn ignition on, with engine off. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S21201878432003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Install fuel cap. Disconnect the FTP sensor. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Is the Fuel Tank Pressure Sensor parameter more than 0.2 volt? If yes, go to next step. If no, go to step 7 .
5. Probe the ground circuit of the FTP sensor with a test light that is connected to battery voltage. Does the test light illuminate? If yes, go to next step. If no, go to step 8 .
6. Measure the voltage of the FTP 5-volt reference circuit with a DVOM. Is the Fuel Tank Pressure Sensor parameter within 4.8-5.2 volts? If yes, go to step 10 . If no, go to step 11 .
7. Test the FTP sensor signal circuit for a short to voltage or for a short to a 5-volt reference circuit. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
8. Test the FTP ground circuit for an open. Did you find and correct the condition? If yes, go to step 14 . If no, go to next step.
9. Test for an intermittent and for a poor connection at the control module. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 13 .
10. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step 14 . If no, go to step 12 .
11. Repair short to voltage in the FTP 5-volt reference circuit. After repairs, go to step 14 .
12. Replace FTP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 14 .
13. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
14. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S21201878432003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
15. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. No MAP sensor DTC P0105, P0107 or P0108.
2. No TP sensor DTC P1120 or P1220.
3. No TFP manual valve position switch DTC P1810.
4. Engine vacuum is 0-15 psi (0-105 kPa).
5. The TP angle is 20-50 percent.
6. Engine speed is 3200-4775 RPM.
7. Transmission is not in PARK or NEUTRAL.

The transmission output speed is less than 150 RPM for 3 seconds.

1. PCM illuminates the Malfunction Indicator Light (MIL) during the second consecutive trip in which the Conditions for Setting DTC are met.
2. PCM commands second gear only.
3. PCM commands maximum line pressure.
4. PCM inhibits TCC engagement.
5. PCM freezes shift adapts from being updated.
6. PCM records the operating conditions when the Conditions for Setting DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
7. PCM stores DTC P0502 in PCM history during the second consecutive trip in which the Conditions for Setting DTC are met.

1. PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
2. Use scan tool can clear the MIL/DTC.
3. PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
4. The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Install scan tool. Turn ignition on, with engine off. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Raise and support the rear axle assembly. Start engine. Place the transmission in any drive range. With drive wheels rotating, does scan tool Transmission OSS increase with the drive wheel speed? If yes, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no, go to next step.
3. Turn ignition off. Disconnect the PCM connector C2. Using DVOM and the GM Terminal Test Kit (J-35616-A), measure the resistance between harness connector terminals C2-2 and C2-10. Does the resistance measure 1377-3355 ohms (2WD) or 976-2354 ohms (4WD)? If yes, go to next step. If no, go to step 7 .
4. Place transmission in Neutral. Select AC volts. Prevent one rear wheel from turning. Rotate the other rear wheel by hand, ensuring that the driveshaft is turning. Does the voltage measure greater than 0.5 volt? If yes, go to next step. If no, go to step 12 .
5. Measure the resistance from terminal C2-10 to ground. Does the resistance measure greater than 50 k/ohms? If yes, go to next step. If no, go to step 9 .
6. Reconnect the PCM connector C2. Disconnect the engine wiring harness from the VSS assembly. Turn ignition on, with engine off. Test the high circuit (CKT 821) of the VSS assembly for a short to power. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
7. Disconnect the engine wiring harness from the VSS assembly. Measure the resistance of the VSS assembly. Does the resistance measure 1377-3355 ohms (2WD) or 976-2354 ohms (4WD)? If yes, go to next step. If no, go to step 13 .
8. Was the resistance measured in step 3 greater than 3355 ohms (2WD) or 2354 ohms (4WD)? If yes, go to step 10 . If no, go to step 11 .
9. Test the high circuit (CKT 821) of the VSS assembly for a short to ground. Repair as necessary. After repairs, go to step 15 .
10. Test the high circuit (CKT 821) of the VSS assembly for an open. Test the low circuit (CKT 822) of the VSS assembly for an open. Repair as necessary. After repairs, go to step 15 .
11. Test the high circuit (CKT 821) and the low circuit (CKT 822) of the VSS assembly for a short together. Repair as necessary. After repairs, go to step 15 .
12. Remove the VSS assembly. See appropriate SERVICING article in AUTOMATIC TRANSMISSION. Inspect the output shaft speed sensor rotor for damage or misalignment. Inspect the case extension bushing for wear. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
13. Replace VSS assembly. After repairs, go to step 15 .
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Perform the following procedure in order to verify the repair: Select DTC. Select Clear Info. Operate the vehicle, so that the transmission output speed is greater than 250 RPM for 2 seconds. Select Specific DTC. Enter DTC P0502. Has the test run and passed? If yes, go to next step. If no, go to step 2 .
16. Using scan tool, observe the stored information, capture info, and DTC Info. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. No TFP manual valve position switch DTC P1810.
2. Engine speed is greater than 450 RPM.
3. Time since the last gear range change is greater than 6 seconds.
4. Time since the last 4WD low state change is greater than 6 seconds.
5. Transmission output speed rise does not exceed 600 RPM within 2 seconds.

1. Transmission output speed drop is greater than 1300 RPM for 3 seconds when the transmission is not in PARK or NEUTRAL.
2. Transmission output speed drop is greater than 8129 RPM for 409 seconds when the transmission is in PARK or NEUTRAL.

1. PCM illuminates the Malfunction Indicator Light (MIL) during the second consecutive trip in which the Conditions for Setting DTC are met.
2. PCM commands a soft landing to second gear.
3. PCM commands maximum line pressure.
4. PCM inhibits TCC engagement.
5. PCM inhibits 4th gear if the transmission is in hot mode.
6. PCM freezes transmission adapt functions.
7. PCM records the operating conditions when the Conditions for Setting DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
8. PCM stores DTC P0503 in PCM history during the second consecutive trip in which the Conditions for Setting DTC are met.

1. PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
2. A scan tool can clear the MIL/DTC.
3. PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
4. PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Install scan tool. Turn ignition on, with engine off. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Raise and support the rear axle assembly. Start engine. Place the transmission in D3 range. With drive wheels rotating, slowly accelerate engine to 2000 RPM and hold speed. Does scan tool Transmission OSS drop or fluctuate more than 1300 RPM? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Turn ignition off. Disconnect the PCM connector C2. Using DVOM and the GM Terminal Test Kit (J-35616-A), measure the resistance between harness connector terminals C2-2 and C2-10. Does the resistance measure 1377-3355 ohms (2WD) or 976-2354 ohms (4WD)? If yes, go to next step. If no, go to step 7 .
4. Place transmission in NEUTRAL. Select AC volts. Prevent one rear wheel from turning. Rotate the other rear wheel by hand, ensuring that the driveshaft is turning. Does the voltage measure greater than 0.5 volt? If yes, go to next step. If no, go to step 12 .
5. Measure the resistance from terminal C2-10 to ground. Does the resistance measure greater than 50 k/ohms? If yes, go to next step. If no, go to step 9 .
6. Reconnect the PCM connector C2. Disconnect the engine wiring harness from the VSS assembly. Turn ignition on, with engine off. Test the high circuit (CKT 821) of the VSS assembly for a short to power. Test the low circuit (CKT 822) of the VSS assembly for a short to power. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 14 .
7. Disconnect the engine wiring harness from the VSS assembly. Measure the resistance of the VSS assembly. Does the resistance measure 1377-3355 ohms (2WD), or 976-2354 ohms (4WD)? If yes, go to next step. If no, go to step 13 .
8. Was the resistance measured in step 3 greater than 3355 ohms (2WD), or 2354 ohms (4WD)? If yes, go to step 10 . If no, go to step 11 .
9. Test the high circuit (CKT 821) of the VSS assembly for a short to ground. Test the low circuit (CKT 822) of the VSS assembly for a short to ground. Repair as necessary. After repairs, go to step 15 .
10. Test the high circuit (CKT 821) of the VSS assembly for an open. Test the low circuit (CKT 822) of the VSS assembly for an open. Repair as necessary. After repairs, go to step 15 .
11. Test the high circuit (CKT 821) and the low circuit (CKT 822) of the VSS assembly for a short together. Repair as necessary. After repairs, go to step 15 .
12. Remove VSS assembly. See appropriate SERVICING article in AUTOMATIC TRANSMISSION. Inspect the output shaft speed sensor rotor for damage or misalignment. Inspect the case extension bushing for wear. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
13. Replace VSS assembly. After repairs, go to step 15 .
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Perform the following procedure in order to verify the repair: Select DTC. Select Clear Info. Operate the vehicle, ensuring that the transmission output speed drop is less than 500 RPM for 2 seconds and output speed is greater than 500 RPM for 2 seconds. Select Specific DTC. Enter DTC P0503. Has the test run and passed? If yes, go to next step. If no, go to step 2 .
16. Using scan tool, observe the stored information, capture info, and DTC Info. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Inspect for ABS DTCs. A faulty ABS condition may contribute to setting DTC P0503.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0130, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0336, P0440, P0442, P0446, P0452, P0453, P0502, P0503, P1120, P1220, P1221, P1512, P1514, P1515, P1516, P1635, or P1639 not set.
2. Engine is operating for at least 2 seconds.
3. Engine Coolant Temperature (ECT) is more than -40°F (-40°C).
4. Intake Air Temperature (IAT) is more than -40°F (-40°C).
5. Barometric (BARO) pressure is more than 19 in. Hg (65 kPa).
6. System voltage is 9-18 volts.
7. Vehicle speed is less than 3 MPH.

1. The actual idle speed is about 150 RPM lower than the desired idle speed.
2. Condition present for 15 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start engine. With scan tool, command the engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. Exit the RPM control function. Does the engine speed correspond, within 100 RPM, with each command? If yes, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no, go to next step.
3. Inspect for any condition that can reduce idle speed by increasing engine load. Examples include: Incorrect Torque Converter Clutch (TCC) operation. Accessories that require additional torque to operate. Restricted exhaust. Mechanical conditions that limit engine speed. After repairs, go to next step.
4. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S05468379322003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
5. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0130, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0336, P0440, P0442, P0446, P0452, P0453, P0502, P0503, P1120, P1220, P1221, P1512, P1514, P1515, P1516, P1635, or P1639 not set.
2. Engine is operating for at least 2 seconds.
3. Engine Coolant Temperature (ECT) is more than -40°F (-40°C).
4. Intake Air Temperature (IAT) is more than -40°F (-40°C).
5. Barometric (BARO) pressure is more than 19 in. Hg (65 kPa).
6. System voltage is 9-18 volts.
7. The vehicle speed is less than 3 MPH.

1. The actual idle speed is about 100 RPM greater than the desired idle speed.
2. Condition present for 15 seconds.

1. The control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails. The control module records the operating conditions at the time the diagnostic fails.
2. Control module stores this information in the Freeze Frame and/or the Failure Records.
3. Control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Start engine. Command engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM with scan tool. Exit the RPM control function. Does the engine speed correspond, within 100 RPM, with each command? If yes, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no, go to next step.
3. Inspect for the following conditions: Vacuum leaks. Excessive deposits in the throttle body. A faulty PCV valve. After inspection or repair, go to next step.
4. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S21917423662003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
5. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Is DTC P0602 set? If yes, go to next step. If no, go to step 5 .
3. Program the PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. Does DTC P0602 reset? If yes, go to next step. If no, go to step 6 .
4. Ensure that all tool connections are secure. Ensure the programming equipment is operating correctly. Ensure the correct software and the correct calibration is used. Attempt to program the PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. Does DTC P0602 reset? If yes, go to next step. If no, go to step 6 .
5. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
6. Turn ignition on, with engine off. Use scan tool in order to clear DTCs. Turn ignition off for 30 seconds. Start engine. Does scan tool display any DTCs? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
7. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The ignition switch is in the crank or run position.
2. DTC P1635 is not set.
3. The ignition voltage is greater than 5.23 volts.

TP sensor 1 voltage is less than 0.27 volts or more than 4.67 volts as observed on scan tool.

1. Control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. Control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. Control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. PCM will turn OFF the Malfunction Indicator Light (MIL) during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. With scan tool, observe the TP sensor voltage with the accelerator pedal in the rest position. Does scan tool indicate voltage less than 0.27 volt or greater than 4.67 volts? If yes, go to step 5 . If no, go to next step.
3. Is DTC P1221 also set? If yes, see «DTC P1221: THROTTLE POSITION SENSORS 1 & 2 CORRELATION»(ref-155898-S27575514242003062800000) . If no, 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 DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S25953110242003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Turn ignition off. Disconnect the throttle body harness connector. Turn ignition on, with engine off. With scan tool, observe the TP sensor 1 voltage parameter. Does scan tool indicate voltage at zero volts? If yes, go to next step. If no, go to step 11 .
6. Connect a fused jumper wire between the TP sensor 5-volt reference circuit and the TP sensor signal circuit at the throttle body harness connector. With scan tool, observe the TP sensor 1 voltage parameter. Does scan tool indicate the TP sensor 1 voltage at 5 volts? If yes, go to next step. If no, go to step 8 .
7. With a test light connected to battery voltage, probe the TP sensor low reference circuit. Does the test light illuminate? If yes, go to step 17 . If no, go to step 13 .
8. With a DVOM, measure the voltage of the TP sensor 1 5-volt reference circuit. Does the DVOM indicate voltage at 5 volts? If yes, go to step 10 . If no, go to next step.
9. Does the DVOM indicate voltage less than 5 volts on the TP sensor 1 5-volt reference circuit? If yes, go to step 14 . If no, go to step 16 .
10. Test the TP sensor 1 signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 12 .
11. Test the TP sensor 1 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 19 .
12. Test the TP sensor 1 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 19 .
13. Test the TP sensor 1 low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to step 19 .
14. Test the TP sensor 1 5-volt reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 21 . If no, go to next step.
15. Test the TP sensor 1 5-volt reference circuit for a short to ground. Repair as necessary. After repairs, go to step 21 . If no, go to step 19 .
16. Test the TP sensor 1 5-volt reference circuit for a short to voltage. Repair as necessary. After repairs, go to step 21 .
17. Inspect for poor connections at the throttle body harness connector. Did you find and correct the condition? If yes, go to step 21 . If no, go to next step.
18. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 21 .
19. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 21 . If no, go to next step.
20. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
21. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S25953110242003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
22. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT Sensor parameter is more than 158°F (70°C).
3. Engine Speed parameter is 1000-2500 RPM.
4. Ignition 1 Signal parameter is more than 10 volts.
5. Engine Run Time parameter is more than 200 seconds.
6. Loop Status parameter is closed.
7. TP sensor Indicated Angle parameter is 5-30 percent.
8. EVAP Purge Solenoid command is more than 10 percent.
9. Fuel level sensor parameter is more than 10 percent.
10. MAP sensor parameter is 7.4-31.0 in. Hg (25-104 kPa).
11. Air Flow Calculated parameter is more than 16 g/s.
12. Conditions are met for 60 seconds.

The HO2S 1 rich to lean counts is less than 2 or lean to rich counts is less than 2.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate engine at normal operating temperature. Operate engine at greater than 1200 RPM for 2 minutes. Observe the HO2S 1 voltage parameter with a scan tool. Does the scan tool indicate that the HO2S 1 voltage is varying greater than and less than 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S42666412312003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 1. Turn ignition on, with engine off. Measure the voltage of the HO2S 1 high signal circuit on the PCM side to a good ground with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to next step. If no, go to step 9 .
5. Turn ignition off. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit and HO2S 1 low signal circuit. Turn ignition on. Monitor the HO2S 1 voltage for the sensor that applies to this DTC with the scan tool. Does the scan tool indicate that the HO2S 1 voltage is less than 20 mV? If yes, go to next step. If no, go to step 10 .
6. Turn ignition off. Remove the 3-amp fused jumper wire. Connect a test light between the ignition 1 voltage circuit and a good ground. DO NOT use the HO2S 1 heater low control. Turn ignition on, with engine off. Does the test light illuminate? If yes, go to next step. If no, go to step 11 .
7. Connect a test light between the ignition 1 voltage circuit and the HO2S 1 heater low control circuit. Turn ignition on, with engine off. Command the HO2S 1 heater ON and OFF with the scan tool. Does the test light turn ON and OFF with each command? If yes, go to step 14 . If no, go to next step.
8. Does the test light remain illuminated with each command? If yes, go to step 12 . If no, go to step 13 .
9. Test the HO2S 1 high signal circuit for an open, high resistance, short to ground, or short to voltage. Did you find and correct the condition. If yes, go to step 19 . If no, go to step 16 .
10. Test the HO2S 1 low signal circuit for an open, short to voltage, or high resistance. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
11. Test the ignition 1 voltage circuit for an open, short to ground, or high resistance. Replace O2 fuse, if necessary. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 15 .
12. Test the HO2S 1 heater low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
13. Test the HO2S 1 heater low control circuit for an open, short to voltage, or high resistance. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
14. Inspect for incorrect use of silicone RTV sealant, fuel contamination, exhaust leak, HO2S installed incorrectly, or damaged wiring. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
15. Inspect for poor connections at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
16. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 18 .
17. Replace HO2S 1. After replacing sensor, go to step 19 .
18. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
19. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S42666412312003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
20. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. ECT sensor parameter is more than 158°F (70°C).
3. Engine speed parameter is 1000-2500 RPM.
4. Ignition 1 signal parameter is more than 10 volts.
5. Engine run time parameter is more than 200 seconds.
6. Loop status parameter is closed.
7. TP sensor Indicated Angle parameter is 5-30 percent.
8. EVAP purge solenoid command is more than 10 percent.
9. Fuel level sensor parameter is more than 10 percent.
10. MAP sensor parameter is 7.4-31.0 in. Hg (25-104 kPa).
11. Air flow calculated parameter is more than 16 g/s.
12. Conditions are met for 60 seconds.

The HO2S 1 rich-to-lean counts is less than 2 or lean-to-rich counts is less than 2.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate engine at normal operating temperature. Operate engine at greater than 1200 RPM for 2 minutes. Observe the HO2S 1 voltage parameter with scan tool. Does scan tool indicate that the HO2S 1 voltage is varying greater than and less than 350-550 mV? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S37892195352003070300000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 1. Turn ignition on, with engine off. Measure the voltage of the HO2S 1 high signal circuit on the PCM side to a good ground with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to next step. If no, go to step 9 .
5. Turn ignition off. Connect a 3-amp fused jumper wire between the HO2S 1 high signal circuit and the HO2S 1 low signal circuit. Turn ignition on. Monitor the HO2S 1 voltage for the sensor that applies to this DTC with scan tool. Does the scan tool indicate that the HO2S 1 voltage is less than 20 mV? If yes, go to next step. If no, go to step 10 .
6. Turn ignition off. Remove the 3-amp fused jumper wire. Connect a test light between the ignition 1 voltage circuit and a good ground. DO NOT use the HO2S 1 heater low control circuit. Turn ignition on, with engine off. Does the test light illuminate? If yes, go to next step. If no, go to step 11 .
7. Connect a test light between the ignition 1 voltage circuit and the HO2S 1 heater low control circuit. Turn ignition on, with engine off. Command the HO2S 1 heater ON and OFF with the scan tool. Does the test light turn ON and OFF with each command? If yes, go to step 14 . If no, go to next step.
8. Does the test light remain illuminated with each command? If yes, go to step 12 . If no, go to step 13 .
9. Test the HO2S 1 high signal circuit for an open, high resistance, short to ground, or short to voltage. Did you find and correct the condition. If yes, go to step 19 . If no, go to step 16 .
10. Test the HO2S 1 low signal circuit for an open, short to voltage, or high resistance. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
11. Test the ignition 1 voltage circuit for an open, short to ground, or high resistance. Replace O2 fuse, if necessary. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 15 .
12. Test the HO2S 1 heater low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
13. Test the HO2S 1 heater low control circuit for an open, short to voltage, or high resistance. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 16 .
14. Inspect for incorrect use of silicone RTV sealant, fuel contamination, exhaust leak, HO2S installed incorrectly, or damaged wiring. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
15. Inspect for poor connections at the harness connector of the HO2S 1. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
16. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 18 .
17. Replace HO2S 1. After replacing sensor, go to step 19 .
18. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
19. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S37892195352003070300000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
20. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0336, P0440, P0446, P0452, P0453, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. The engine is in power enrichment mode.
3. The ignition 1 signal is more than 10 volts.
4. Engine Coolant Temperature (ECT) is greater than 158°F (70°C).
5. Engine is operating in Closed Loop.
6. Fuel level sensor is more than 10 percent.
7. Engine run time is more than 10 seconds.
8. Conditions are met for 5 seconds.

PCM detects that the HO2S 1 parameter is more than 700 mV and HO2S 2 parameter is less than 399 mV for 9.5 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. The PCM will record the operating conditions when the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate engine at normal operating temperature. Operate engine at greater than 1200 RPM for 2 minutes. Observe the HO2S 2 voltage parameter with the scan tool. Does the scan tool indicate that the HO2S 2 voltage is less than 399 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S16400639862003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 2 sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S 2 high signal circuit on the PCM side with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 2 high signal circuit for a short to ground or a short to the low signal circuit. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 2 may be detecting a lean exhaust condition. Inspect HO2S connector for water intrusion, exhaust leak between HO2S 2 and engine, incorrect fuel pressure, lean fuel injectors, or inaccurate MAF sensor. Repair as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 2 sensor. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace HO2S 2. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
11. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S16400639862003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201 P0202, P0203, P0204, P0205, P0206, P0300-P0306, P0336, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P0604, P0606, P1120, P1220, P1221, P1271, P1275, P1280, P1441, P1484, P1512, P1514, P1515, P1516, P1621, P1635, P1639, P1680, or P1681 not set.
2. Engine is in the Decel Fuel Cut-Off (DFCO) mode.
3. Ignition 1 signal is more than 10 volts.
4. Engine Coolant Temperature (ECT) is greater than 158°F (70°C).
5. Fuel level sensor is more than 10 percent.
6. Engine is operating in Closed Loop.
7. Engine run time is more than 10 seconds.

PCM detects that the HO2S 2 parameter is more than 648 mV for more than 10 seconds.

1. The Malfunction Indicator Light (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present.
2. PCM will record the operating conditions when the diagnostic fails. This information will store in the Freeze Frame/Failure Records buffers.
3. A history DTC stores.

1. The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
2. A history DTC will clear after 40 consecutive warm-up cycles without a fault.
3. Use scan tool in order to clear the DTCs.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate engine at normal operating temperature. Operate engine at greater than 1200 RPM for 2 minutes. Observe the HO2S 2 voltage parameter with scan tool. Does the scan tool indicate that the HO2S 2 voltage is more than 648 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S03507616902003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the HO2S 2 sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S high signal circuit on the PCM side with a DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 2 high signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 2 is detecting a rich condition or may be contaminated. Inspect HO2S connector for water intrusion, silicone contaminated HO2S 2, fuel contaminated engine oil, incorrect fuel pressure, leaking fuel pressure regulator, or rich fuel injectors. Repair any of the conditions as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 2. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace HO2S. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S03507616902003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0122, P0123, P0131, P0132, P0133, or P0134 not set.
2. Engine Coolant Temperature (ECT) is more than 70°F (20°C).
3. Engine has been running for longer than 20 seconds.
4. Engine is operating in a Closed Loop operation.
5. Engine is in the power enrichment mode.

PCM detects that the HO2S 1 parameter is less than 300 mV for 5 seconds.

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

Conditions For Clearing DTC

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Operate engine at normal operating temperature. Operate engine at greater than 1200 RPM for 2 minutes. Observe the HO2S 1 voltage parameter with a scan tool. Does the scan tool indicate that the HO2S 1 voltage is less than 300 mV? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S10528379162003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(ref-155898-S15827103112003062800000) .
4. Turn ignition off. Disconnect the HO2S sensor. Turn ignition on, with engine off. Measure the voltage of the HO2S 1 high signal circuit on the PCM side with the DVOM. Does the voltage measure within 350-550 mV? If yes, go to step 6 . If no, go to next step.
5. Test the HO2S 1 high signal circuit for a short to ground or a short to the HO2S 1 low signal circuit. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 8 .
6. The HO2S 1 is detecting a lean condition or may be contaminated. Inspect HO2S connector for water intrusion, silicone contaminated HO2S, exhaust leak between HO2S 1 and engine, vacuum leaks, incorrect fuel pressure, or lean fuel injectors. Repair any of the conditions as necessary. Did you find and correct the condition? If yes, go to step 11 . If no, go to next step.
7. Inspect for poor connections at the harness connector of the HO2S 1 sensor. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 9 .
8. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 11 . If no, go to step 10 .
9. Replace HO2S 1. After replacing sensor, go to step 11 .
10. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
11. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S10528379162003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
12. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. A restricted fuel filter can supply adequate amounts of fuel at idle, but may not be able to supply enough fuel during heavy acceleration. Water or alcohol in the fuel may cause low HO2S 1 voltage during acceleration.
2. High resistance in ignition coil control circuits may cause this condition.
3. High resistance in MAP sensor circuits may cause this condition.
4. Check for faulty or plugged fuel injectors.

1. The ignition switch in the crank or run position.
2. DTC P1635 is not set.
3. The ignition voltage is more than 5.23 volts.

The TP sensor 2 voltage is less than 0.31 volt or more than 4.7 volts.

1. The control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails.
3. The control module stores this information in the Freeze Frame and/or the Failure Records. The control module commands the TAC system to operate in the Reduced Engine Power mode or under certain conditions, the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. PCM will turn OFF the Malfunction Indicator Light (MIL) during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. With scan tool, observe the TP sensor voltage with the accelerator pedal in the rest position. Does scan tool indicate voltage less than 0.31 volt or greater than 4.7 volts? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S14953389312003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the throttle body harness connector. Turn ignition on, with engine off. With scan tool, observe the TP sensor 2 voltage parameter. Does scan tool indicate voltage at 5 volts? If yes, go to next step. If no, go to step 12 .
5. With a test light connected to ground, probe the TP sensor signal circuit. Does the test light illuminate? If yes, go to step 12 . If no, go to next step.
6. With a test light still connected to the TP sensor signal circuit, observe the TP sensor 2 parameter. Does scan tool indicate voltage at zero volts? If yes, go to next step. If no, go to step 11 .
7. With a DVOM, measure the voltage of the TP sensor 2 5-volt reference circuit. Does the DVOM indicate voltage at 5 volts. If yes, go to next step. If no, go to step 10 .
8. With a test light connected to battery voltage, probe the TP sensor low reference circuit. Does the test light illuminate? If yes, go to next step. If no, go to step 14 .
9. Test the TP sensor low reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 18 .
10. Does the DVOM indicate voltage less than 5 volts on the TP sensor 2 5-volt reference circuit? If yes, go to step 15 . If no, go to step 17 .
11. Test the TP sensor 2 signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 13 .
12. Test the TP sensor 2 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
13. Test the TP sensor 2 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
14. Test the TP sensor 2 low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
15. Test the TP sensor 2 5-volt reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 22 . If no, go to next step.
16. Test the TP sensor 2 5-volt reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
17. Test the TP sensor 2 5-volt reference circuit for a short to voltage. Repair as necessary. After repairs, go to step 22 .
18. Inspect for poor connections at the throttle body harness connector. Did you find and correct the condition? If yes, go to step 22 . If no, go to next step.
19. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 22 .
20. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 22 . If no, go to next step.
21. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
22. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S14953389312003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
23. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The ignition is ON.
2. DTCs P1120, P1220, P1635, or P1639 not set.
3. The ignition voltage is greater than 5.23 volts.

The difference between the TP sensor 1 and TP sensor 2 exceeds a predetermined value.

1. Control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. Control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. Control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. PCM will turn OFF the Malfunction Indicator Light (MIL) during the third consecutive trip in which the diagnostic has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Using scan tool, observe the DTC information. Is DTC P1635 or P1639 also set? If yes, see «DTC P1635: 5-VOLT REFERENCE "A" CIRCUIT»(ref-155898-S28470144352003062800000) or «DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT»(ref-155898-S02536990042003062800000) . If no, go to next step.
3. Turn ignition on, with engine off. Monitor the TP sensors Agree/Disagree parameter using scan tool. Does scan tool indicate Disagree? If yes, go to step 6 . If no, go to next step.
4. Remove the resonator assembly from the throttle body assembly. Remove the ETC fuse. Open the throttle blade to Wide-Open Throttle (WOT) by hand and then return it to closed throttle. Stop briefly at about 25 percent, 50 percent, 75 percent and 100 percent in each direction. Test the Throttle Sensors Disagree parameter at each stop. Does scan tool indicate Disagree while rotating the throttle blade? If yes, go to step 6 . If no, go to next step.
5. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S28789429802003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
6. Disconnect the TP sensor electrical connector. Turn ignition on, with engine off. Measure the voltage between the 5-volt reference circuit of TP sensor 1 and TP sensor 1 low reference circuit with a DVOM. Measure the voltage between the 5-volt reference circuit of TP sensor 2 and TP sensor 2 low reference circuit with a DVOM. Does the DVOM display a voltage 4.9-5.1 volts for both measurements? If yes, go to step 8 . If no, go to next step.
7. Test the voltage on the 5-volt reference circuit for TP sensor 1 and 2 to battery ground with a DVOM. Does the DVOM display a voltage 4.9-5.1 volts? If yes, go to step 10 . If no, go to step 9 .
8. Observe the TP sensor 1 and 2 angle on scan tool. Does scan tool indicate both sensors at 100 percent? If yes, go to step 12 . If no, go to step 11 .
9. Test the 5-volt reference circuit of the TP sensor 1 and 2 for high resistance. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
10. Test the low reference circuit of the TP sensor 1 and 2 for high resistance. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
11. Test the signal circuit of the TP sensor 1 and 2 for high resistance. Did you find and correct the condition? If yes, go to step 15 . If no, go to step 13 .
12. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 15 .
13. Test for poor connections and/or terminal tension at the TP sensor and at the PCM. Did you find and correct the condition? If yes, go to step 15 . If no, go to next step.
14. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
15. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S28789429802003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
16. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

If DTC is determined to be intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. The battery voltage is more than 5.23 volts.
2. DTCs P1275, P1280, P1635, or P1639 not set.
3. The accelerator pedal is leaving the idle position.

The voltage difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value.

1. The control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. PCM turns OFF the MIL after 3 consecutive drive trips that the diagnostic runs and does not fail.
2. A History DTC clears after 40 consecutive warm up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.
3. The scan tool clears the MIL/DTC.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Using scan tool, observe the DTC information. Is DTC P1120, P1220, P1275, P1280, P1635, or P1639 also set? If yes, see «DTC P1120: THROTTLE POSITION SENSOR 1 CIRCUIT»(ref-155898-S42779905142003062800000) , «DTC P1220: THROTTLE POSITION SENSOR 2 CIRCUIT»(ref-155898-S02577458542003062800000) , «DTC P1275: ACCELERATOR PEDAL POSITION CIRCUIT (SENSOR 1)»(ref-155898-S24503802972003062800000) , «DTC P1280: ACCELERATOR PEDAL POSITION CIRCUIT (SENSOR 2)»(ref-155898-S19963277472003062800000) , «DTC P1635: 5-VOLT REFERENCE "A" CIRCUIT»(ref-155898-S28470144352003062800000) or «DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT»(ref-155898-S02536990042003062800000) . If no, go to next step.
3. Turn ignition off. Disconnect the APP sensor electrical connector. Disconnect the PCM. Use a DVOM to measure the resistance of the following circuits for each of the APP sensors: Low reference circuit. Signal circuit. 5-volt reference circuit. Did any of the circuits measure more than 5 ohms? If yes, go to step 5 . If no, go to next step.
4. Test for a short between any of the circuits in the APP sensor harness. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step 7 . If no, go to step 6 .
5. Repair high resistance in the circuit. After repairs, go to step 7 .
6. Replace APP sensor. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to next step.
7. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S24877986602003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
8. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The PCM compares the signal of each of the accelerator pedal position sensors to each other throughout the entire range of operation. Clear the DTCs and actuate the pedal through the entire range with the ignition ON and engine OFF. Use the Connector Test Adapter Kit (J-35616-A) for any test that requires probing the PCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

If DTC is determined to be intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. The ignition is ON.
2. The ignition voltage is greater than 5.23 volts.
3. DTC P1635 is not set.

The APP sensor 1 voltage is less than 0.13 volt or more than 4.87 volts.

1. The control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. With scan tool observe the APP sensor 1 voltage with the accelerator pedal in the rest position. Does scan tool indicate voltage less than 0.13 volt or greater than 4.87 volts? If yes, go to step 4 . If no, go to next step.
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S29098466692003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the accelerator pedal harness connector. Turn ignition on, with engine off. With scan tool, observe the APP sensor 1 voltage parameter. Does scan tool indicate voltage at zero volts? If yes, go to next step. If no, go to step 10 .
5. Connect a fused jumper wire between the APP sensor 1 5-volt reference circuit and the APP sensor 1 signal circuit at the accelerator pedal harness connector. With scan tool, observe the APP sensor 1 voltage parameter. Does scan tool indicate the APP sensor 1 voltage at 5 volts? If yes, go to next step. If no, go to step 7 .
6. With a test light connected to battery voltage, probe the APP sensor low reference circuit. Does the test light illuminate? If yes, go to step 16 . If no, go to step 12 .
7. With a DVOM, measure the voltage of the APP sensor 1 5-volt reference circuit. Does the DVOM indicate voltage at 5 volts? If yes, go to step 9 . If no, go to next step.
8. Does the DVOM indicate voltage less than 5 volts on the APP sensor 1 5-volt reference circuit? If yes, go to step 13 . If no, go to step 15 .
9. Test the APP sensor 1 signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 11 .
10. Test the APP sensor 1 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 18 .
11. Test the APP sensor 1 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 18 .
12. Test the APP sensor 1 low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 18 .
13. Test the APP sensor 1 5-volt reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 20 . If no, go to next step.
14. Test the APP sensor 1 5-volt reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step 20 . If no, go to step 18 .
15. Test the APP sensor 1 5-volt reference circuit for a short to voltage. Repair as necessary. After repairs, go to step 20 .
16. Inspect for poor connections at the accelerator pedal harness connector. Did you find and correct the condition? If yes, go to step 20 . If no, go to next step.
17. Replace accelerator pedal assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 20 .
18. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 20 . If no, go to next step.
19. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
20. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S29098466692003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
21. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. The ignition is ON.
2. Ignition voltage is greater than 5.23 volts.
3. DTC P1635 is not set.

The APP sensor 2 voltage is less than 0.13 volt or more than 4.87 volts.

1. The control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. With scan tool, observe the APP sensor 2 voltage with the accelerator pedal in the rest position. Does scan tool indicate voltage less than 0.13 volt or greater than 4.87 volts? If yes, go to step 5 . If no, go to next step.
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 DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S38809525612003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Turn ignition off. Disconnect the accelerator pedal harness connector. Turn ignition on, with engine off. With scan tool, observe the APP sensor 2 voltage parameter. Does scan tool indicate voltage at 5 volts? If yes, go to next step. If no, go to step 12 .
5. With a test light connected to ground, probe the APP sensor 2 signal circuit. Does the test light illuminate? If yes, go to step 11 . If no, go to next step.
6. With the test light still connected to the APP sensor 2 signal circuit, observe the APP sensor 2 parameter. Does scan tool indicate voltage at zero volts? If yes, go to next step. If no, go to step 11 .
7. With a DVOM, measure the voltage of the APP sensor 2 5-volt reference circuit. Does the DVOM indicate voltage at 5 volts? If yes, go to next step. If no, go to step 10 .
8. With a test light connected to battery voltage, probe the APP sensor 2 low reference circuit. Does the test light illuminate? If yes, go to next step. If no, go to step 14 .
9. Test the APP sensor low reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 18 .
10. Does the DVOM indicate voltage less than 5 volts on the APP sensor 2 5-volt reference circuit? If yes, go to step 14 . If no, go to step 16 .
11. Test the APP sensor 2 signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 13 .
12. Test the APP sensor 2 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
13. Test the APP sensor 2 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
14. Test the APP sensor 2 low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
15. Test the APP sensor 2 5-volt reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 22 . If no, go to next step.
16. Test the APP sensor 2 5-volt reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step 22 . If no, go to step 20 .
17. Test the APP sensor 2 5-volt reference circuit for a short to voltage. Repair as necessary. After repairs, go to step 22 .
18. Inspect for poor connections at the accelerator pedal harness connector. Did you find and correct the condition? If yes, go to step 22 . If no, go to next step.
19. Replace accelerator pedal assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 22 .
20. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step 22 . If no, go to next step.
21. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
22. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S38809525612003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
23. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. DTCs P0013, P0014, P0335, P0336, P0340, P0341, or P1345 not set.
2. The engine coolant temperature is more than 158°F (70°C).

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

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Perform the crankshaft position system variation learn procedure. See «CRANKSHAFT POSITION SENSOR»(ref-155898-S34895643712003062800000) under PROGRAMMING. Is the action complete? If yes, go to step 4 . If no, go to next step.
3. If the crankshaft position system variation learn procedure cannot be performed successfully, check for a damaged reluctor wheel, excessive crankshaft runout, damaged crankshaft, interference in the signal circuit of the CKP sensor, or ECT is less than 158°F (70°C). DTC will also set when ignition switch is left in ON position until battery is drained. If PCM power was disconnected with ignition ON, it may erase the stored value and set DTC P1336. Repair as necessary. After repairs, go to next step.
4. Clear the DTCs with scan tool. Turn ignition off. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S00435023582003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
5. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. Engine is running.
2. Engine has been running for more than 16 seconds.
3. Minimum voltage is 11 volts.
4. Variable cam phaser is commanded to zero.

The deviation between the crankshaft and camshaft positions exceeds a calibrated amount.

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

1. PCM will turn OFF the Malfunction Indicator Light (MIL) during the third consecutive trip in which the diagnostic has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool. Start the engine. Does scan tool indicate that DTC P0014 failed this ignition? If yes, see «DTC P0014: CAMSHAFT POSITION "B" TIMING OVER ADVANCED OR SYSTEM PERFORMANCE (BANK 1)»(ref-155898-S30751762232003062800000) . If no, go to next step.
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 DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S03536128382003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S18899605602003062800000) .
4. Turn ignition off. Inspect the crank damper bolt for the proper torque. Did you find and correct the condition? If yes, go to step 9 . If yes, go to next step.
5. Disconnect the camshaft position actuator. Remove the Camshaft Position (CMP) actuator solenoid. Jumper the camshaft position solenoid actuator high control circuit of the actuator solenoid assembly to 12 volts. Jumper the low reference circuit of the camshaft position actuator solenoid to a good ground. Does the pintle inside the CMP actuator solenoid move? If yes, go to next step. If no, go to step 8 .
6. Inspect the CMP actuator for binding or being stuck. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
7. Inspect the engine for correct valve timing. Did you find and correct the condition? If yes, go to step 9 . If no, see «DIAGNOSTIC AIDS»(ref-155898-S18899605602003062800000) .
8. Replace the camshaft position actuator solenoid. After replacing solenoid, go to next step.
9. Clear the DTCs with scan tool. Turn ignition off. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S03536128382003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
10. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

1. This DTC will only set at idle.
2. An improperly torqued harmonic balancer or improperly built engine will set this DTC.
3. PCM will disable the ability to command the variable cam phaser on scan tool. This will prevent engine damage from excessive valve overlap.

1. Vehicle speed is more than 0.6 MPH.
2. Engine load is less than 100 percent.
3. Engine misfire is detected.
4. Engine speed is less than 6500 RPM.

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

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

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

Did you perform the Diagnostic System Check - Engine Controls? If yes, see appropriate ANTI-LOCK article in BRAKES. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

1. Vehicle speed is more than 10 MPH.
2. Engine speed is less than 3200 RPM.
3. Engine load is less than 60 percent.
4. A misfire DTC is occurring and requesting the MIL to be illuminated.

The PCM is detecting a loss of communication with the EBCM for less than 5 seconds.

1. Control module stores the DTC information into memory when the diagnostic runs and fails.
2. PCM will not illuminate the Malfunction Indicator Light (MIL).
3. PCM will store the conditions present when the DTC set as Failure Records data only.
4. The driver information center, if equipped, may display a message.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using scan tool Clear DTC Information function.

Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

1. DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0440, P0442, P0446, P0452, or P0453 not set.
2. The ignition voltage is 10-18 volts.
3. Barometric (BARO) pressure is more than 22 in. Hg (75 kPa).
4. Fuel level is 15-85 percent.
5. Engine Coolant Temperature (ECT) is 39-86°F (4-30°C).
6. Intake Air Temperature (IAT) is 39-86°F (4-30°C).
7. Start up ECT and IAT are within 16°F (9°C) of each other.
8. Vehicle Speed Sensor (VSS) is less than 75 MPH.

The control module detects vacuum during a non-purge condition.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Disconnect the purge pipe from the EVAP purge solenoid. Install a hand-held vacuum gauge to the EVAP purge solenoid purge port. Disconnect the EVAP purge solenoid harness connector. Monitor vacuum on the vacuum gauge. Start and allow engine to idle. Increase the idle to 1200-1500 RPM. Does the vacuum gauge indicate an increase in vacuum? If yes, go to step 8 . If no, go to next step.
3. Connect the EVAP purge solenoid harness connector. Monitor vacuum on the vacuum gauge. Increase the idle to 1200-1500 RPM. Does the vacuum gauge indicate an increase in vacuum? If yes, go to step 5 . If no, go to next step.
4. Turn ignition off. Remove and then install fuel fill cap. Turn ignition on, with engine off. Observe the Fuel Tank Pressure Sensor parameter with scan tool. Is the Fuel Tank Pressure Sensor parameter within -0.5 to 0.5 in. H2O? If yes, see «DIAGNOSTIC AIDS»(ref-155898-S04474041302003062800000) . If no, go to step 6 .
5. Test the EVAP purge solenoid control circuit for a short to ground. Did you find and correct the conditions? If yes, go to step 9 . If no, go to step 8 .
6. Test for an intermittent and for a poor connection at the EVAP purge solenoid. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
7. Replace FTP sensor. After replacing sensor, go to step 9 .
8. Replace EVAP canister purge solenoid. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) . After replacing solenoid, go to next step.
9. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S11285390492003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2 . If no, go to next step.
10. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

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

The ignition is ON.

The difference between the predicted and the actual throttle position is more than a calibrated amount.

1. Control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. Control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. Control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. PCM turns OFF the MIL after 3 consecutive drive trips that the diagnostic runs and passes.
2. A History DTC clears after 40 consecutive warm-up cycles in which there are no failures reported of this diagnostic or any other emission related diagnostic.
3. The scan tool clears the MIL/DTC.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are DTCs P1120, P1220, P1221, P1271, P1275 and P1280 also set? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
3. Turn ignition on, with engine off. Observe the TP sensor 1 and 2 angle parameters. Apply and release the accelerator pedal several times. Does the TP sensor 1 and 2 angle parameters increase as the pedal is applied and decrease as the pedal is released? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records for this DTC. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S04934096702003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S09870361712003062800000) .
5. Turn ignition on, with engine off. Probe both sides of the ETC or TAC fuse with a test light. Does the test light illuminate on both sides of the fuse? If yes, go to next step. If no, go to step 16 .
6. Turn ignition off. Probe both sides of the ETC or TAC fuse with a test light. Does the test light illuminate on both sides of the fuse? If yes, go to step 22 . If no, go to next step.
7. Disconnect the PCM connector containing the ETC/TAC ignition 1 voltage circuit. Turn ON the ignition. Probe the ETC ignition 1 voltage circuit with a test light. Does the test light illuminate? If yes, go to next step. If no, go to step 23 .
8. Inspect the throttle body for throttle valve that is NOT in the rest position, throttle valve that is binding open or closed, or throttle valve that is free to move open or closed WITHOUT spring pressure. Did you find any of these conditions with the throttle body? If yes, go to step 24 . If no, go to next step.
9. Disconnect the throttle body harness connector. Turn ignition on, with engine off. Probe the TAC motor control 1 and 2 circuits with the test light connected to ground. Did the test light illuminate and remain illuminated on either circuit? If yes, go to step 13 . If no, go to next step.
10. Probe the TAC motor control 1 and 2 circuits with the test light connected to battery positive. Did the test light illuminate and remain illuminated on either circuit? If yes, go to step 14 . If no, go to next step.
11. Turn ignition off. Connect the test light between the TAC motor control 1 and battery ground. Observe the test light as you turn ON the ignition. Does the test light flash ON and then turn OFF? If yes, go to next step. If no, go to step 15 .
12. Turn ignition off. Connect a test light between the TAC motor control 2 circuit and battery ground. Observe the test light as you turn ON the ignition. Does the test light flash ON and then OFF? If yes, go to step 18 . If no, go to step 15 .
13. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Turn ignition on, with engine off. Probe the TAC motor control 1 and 2 circuits with the test light connected to ground. Does the test light illuminate? If yes, go to step 20 . If no, go to step 19 .
14. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Probe the TAC motor control 1 and 2 circuits with the test light connected to battery positive. Does the test light illuminate? If yes, go to step 21 . If no, go to step 19 .
15. Turn ignition off. Disconnect the PCM connector that contains the TAC motor controls circuits. Test TAC motor control 1 and 2 circuits for an open or high resistance. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 19 .
16. Test the ETC/TAC ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to next step.
17. Test the motor control 1 circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
18. Test for a poor connection or terminal tension at the throttle body connector. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
19. Test for a poor connection or terminal tension at the PCM. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
20. Repair short to voltage on the circuit where the test light remained illuminated. After repairs, go to step 26 .
21. Repair short to ground on the circuit where the test light remained illuminated. After repairs, go to step 26 .
22. Repair short to voltage on the ETC ignition 1 voltage circuit. After repairs, go to step 26 .
23. Repair open or high resistance in the ETC ignition 1 voltage circuit. After repairs, go to step 26 .
24. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 26 .
25. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
26. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S04934096702003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
27. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The throttle valve is spring loaded to a slightly open position. The throttle valve should be open about 20 percent. This is referred to as the rest position. The throttle valve should not be completely closed nor should they be open any more than the specified amount. The throttle valve should move open and to the closed position without binding under the normal spring pressure. The throttle should NOT be free to move open or closed WITHOUT spring pressure. Replace throttle body if any of these conditions are found. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

Note. Operating the throttle blade with the Throttle Blade Control function of scan tool may cause additional DTCs to set. Do not attempt to diagnose DTCs set during this function.

The scan tool has the ability to operate the throttle control system using Special Functions. Actuate the throttle valve using the throttle blade control function located in the TAC System menu. This function will operate the throttle valve through the entire range in order to determine if the throttle body and system operate correctly. Check for the following conditions

1. Use the Connector Test Adapter Kit (J-35616-A) for any test that requires probing the PCM harness connector or a component harness connector.
2. Poor connections at the PCM or at the component. Inspect the harness connectors for a poor terminal to wire connection. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. DTCs P1512, P1515, P1516, P1523, P1635, or P1639 not set.
2. The engine is running and the engine speed is more than 600 RPM.

PCM detects that the calculated airflow rate is more than expected.

1. The control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. PCM will turn OFF the Malfunction Indicator Light (MIL) during the third consecutive trip in which the diagnostic has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. DTC can be cleared by using scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are any other DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S02979462722003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S35495997292003062800000) .
4. Inspect for the following conditions: Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction. Air leaks at throttle body mounting area and intake manifold sealing surfaces. Did you find and correct the condition? If yes, go to step 8 . If no, go to next step.
5. Allow the engine to reach operating temperature. Observe the MAP sensor voltage parameter with scan tool. Is the MAP sensor voltage 0.8-4.0 volts? If yes, go to next step. If no, see «DTC P0105: MAP SENSOR CIRCUIT - INSUFFICIENT ACTIVITY»(ref-155898-S42645765212003062800000) .
6. Idle engine. Observe the MAP sensor kPa parameter with scan tool. Increase the engine speed slowly and then back to idle. Does the MAP sensor kPa change smoothly and gradually as engine speed is increased and returned to idle? If yes, go to next step. If no, see «DTC P0105: MAP SENSOR CIRCUIT - INSUFFICIENT ACTIVITY»(ref-155898-S42645765212003062800000) .
7. Inspect the throttle body for the following conditions while modulating the throttle through the entire range using scan tool: Loose or damaged throttle blade. Broken throttle shaft. Drive mechanism damage. If any of these conditions exist, replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Did you find and correct the condition? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S35495997292003062800000) .
8. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S02979462722003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
9. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

Inspect for the following conditions

1. Throttle blade for damage.
2. A skewed cam sensor signal. Inspect for signals that are intermittently shorted to ground, causing a fluctuating RPM on scan tool.

If the condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. Ignition is ON.
2. Ignition voltage is greater than 8 volts.
3. System is not in battery saver mode.
4. Engine is running.
5. DTC P1514 is not set.

The difference between the predicted and the actual throttle position is more than a calibrated amount.

1. Control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. Control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. Control module commands the TAC system to operate in the Reduced Engine Power mode or under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. The PCM turns OFF the MIL after 3 consecutive drive trips that the diagnostic runs and passes.
2. A History DTC clears after 40 consecutive warm-up cycles in which there are no failures reported of this diagnostic or any other emission related diagnostic.
3. The scan tool clears the MIL/DTC.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are DTCs P1120, P1220, P1221, P1271, P1275 and P1280 also set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
3. Turn ignition on, with engine off. Observe the TP sensor 1 and 2 angle parameters. Apply and release the accelerator pedal several times. Does the TP sensor 1 and 2 angle parameters increase as the pedal is applied and decrease as the pedal is released? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records for this DTC. Start engine. Operate vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S07448276492003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S33708290582003062800000) .
5. Turn ignition on, with engine off. Probe both sides of the ETC fuse with a test light. Does the test light illuminate on both sides of the fuse? If yes, go to next step. If no, go to step 16 .
6. Turn ignition off. Probe both sides of the ETC/TAC fuse with a test light. Does the test light illuminate on both sides of the fuse? If yes, go to step 22 . If no, go to next step.
7. Turn ignition off. Disconnect the PCM connector containing the ETC/TAC ignition 1 voltage circuit. Turn ON the ignition. Probe the ETC ignition 1 voltage circuit with a test light. Does the test light illuminate? If yes, go to next step. If no, go to step 23 .
8. Turn ignition off. Inspect the throttle body for throttle valve that is NOT in the rest position, throttle valve that is binding open or closed, or throttle valve that is free to move open or closed WITHOUT spring pressure. Did you find any of these conditions with the throttle body? If yes, go to step 24 . If no, go to next step.
9. Disconnect the throttle body harness connector. Turn ignition on, with engine off. Probe the TAC motor control 1 and 2 circuits with the test light connected to ground. Did the test light illuminate and remain illuminated on either circuit? If yes, go to step 13 . If no, go to next step.
10. Probe the TAC motor control 1 and 2 circuits with the test light connected to battery positive. Did the test light illuminate and remain illuminated on either circuit? If yes, go to step 14 . If no, go to next step.
11. Turn ignition off. Connect the test light between the TAC motor control 1 and battery ground. Observe the test light as you turn ON the ignition. Does the test light flash ON and then turn OFF? If yes, go to next step. If no, go to step 15 .
12. Turn ignition off. Connect a test light between the TAC motor control 2 circuit and battery ground. Observe the test light as you turn ON the ignition. Does the test light flash ON and then OFF? If yes, go to step 18 . If no, go to step 15 .
13. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Turn ignition on, with engine off. Probe the TAC motor control 1 and 2 circuits with the test light connected to ground. Does the test light illuminate? If yes, go to step 20 . If no, go to step 19 .
14. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Probe the TAC motor control 1 and 2 circuits with the test light connected to battery positive. Does the test light illuminate? If yes, go to step 21 . If no, go to step 19 .
15. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Test the TAC motor control 1 and 2 circuits for an open or high resistance. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 19 .
16. Test the ETC/TAC ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to next step.
17. Test the motor control 1 circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
18. Test for a poor connection or terminal tension at the throttle body connector. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
19. Test for a poor connection or terminal tension at the PCM. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
20. Repair short to voltage on the circuit where the test light remained illuminated. After repairs, go to step 26 .
21. Repair short to ground on the circuit where the test light remained illuminated. After repairs, go to step 26 .
22. Repair short to voltage on the ETC ignition 1 voltage circuit. After repairs, go to step 26 .
23. Repair open or high resistance in the ETC ignition 1 voltage circuit. After repairs, go to step 26 .
24. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 26 .
25. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
26. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S07448276492003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
27. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The throttle valve is spring loaded to a slightly open position. The throttle valve should be open about 20 percent. This is referred to as the rest position. The throttle valve should not be completely closed nor should they be open any more than the specified amount. The throttle valve should move open and to the closed position without binding under the normal spring pressure. The throttle should NOT be free to move open or closed WITHOUT spring pressure. Replace throttle body if any of these conditions are found. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

Note. Operating the throttle blade with the Throttle Blade Control function of scan tool may cause additional DTCs to set. Do not attempt to diagnose DTCs set during this function.

The scan tool has the ability to operate the throttle control system using Special Functions. Actuate the throttle valve using the throttle blade control function located in the TAC System menu. This function will operate the throttle valve through the entire range in order to determine if the throttle body and system operate correctly. Check for the following conditions

1. Use the Connector Test Adapter Kit (J-35616-A) for any test that requires probing the PCM harness connector or a component harness connector.
2. Poor connections at the PCM or at the component. Inspect the harness connectors for a poor terminal to wire connection.
3. If the condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. Ignition is ON.
2. Ignition voltage is greater than 8 volts.
3. System is not in the battery save mode.
4. Engine is running.
5. DTC P1514 is not set.

The difference between the predicted and the actual throttle position is more than a calibrated amount.

1. Control module illuminates the Malfunction Indicator Light (MIL) when the diagnostic runs and fails.
2. Control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. Control module commands the TAC system to operate in the Reduced Engine Power mode; or, under certain conditions the control module commands the engine OFF.
4. The message center displays Reduced Engine Power.

1. The PCM turns OFF the MIL after 3 consecutive drive trips that the diagnostic runs and passes.
2. A History DTC clears after 40 consecutive warm-up cycles in which there are no failures reported of this diagnostic or any other emission related diagnostic.
3. The scan tool clears the MIL/DTC.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are DTCs P1120, P1220, P1221, P1271, P1275, and P1280 also set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
3. Turn ignition on, with engine off. Observe the TP sensor 1 and 2 angle parameters. Apply and release the accelerator pedal several times. Does the TP sensor 1 and 2 angle parameters increase as the pedal is applied and decrease as the pedal is released? If yes, go to next step. If no, go to step 5 .
4. Observe the Freeze Frame/Failure Records for this DTC. Start the engine. Operate the vehicle within the Conditions For Running the DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S18668387192003062800000) . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-155898-S03763113502003062800000) .
5. Turn ignition on, with engine off. Probe both sides of the ETC fuse with a test light. Does the test light illuminate on both sides of the fuse? If yes, go to next step. If no, go to step 16 .
6. Turn ignition off. Probe both sides of the ETC/TAC fuse with a test light. Does the test light illuminate on both sides of the fuse? If yes, go to step 22 . If no, go to next step.
7. Turn ignition off. Disconnect the PCM connector containing the ETC/TAC ignition 1 voltage circuit. Turn ON the ignition. Probe the ETC/TAC ignition 1 voltage circuit with a test light. Does the test light illuminate? If yes, go to next step. If no, go to step 23 .
8. Turn ignition off. Inspect the throttle body for throttle valve that is NOT in the rest position, throttle valve that is binding open or closed, or throttle valve that is free to move open or closed WITHOUT spring pressure. Did you find any of these conditions with the throttle body? If yes, go to step 24 . If no, go to next step.
9. Disconnect the throttle body harness connector. Turn ignition on, with engine off. Probe the TAC motor control 1 and 2 circuits with the test light connected to ground. Did the test light illuminate and remain illuminated on either circuit? If yes, go to step 13 . If no, go to next step.
10. Probe the TAC motor control 1 and 2 circuits with the test light connected to battery positive. Did the test light illuminate and remain illuminated on either circuit? If yes, go to step 14 . If no, go to next step.
11. Turn ignition off. Connect the test light between the TAC motor control 1 and battery ground. Observe the test light as you turn ON the ignition. Does the test light flash ON and then turn OFF? If yes, go to next step. If no, go to step 15 .
12. Turn ignition off. Connect a test light between the TAC motor control 2 circuit and battery ground. Observe the test light as you turn ON the ignition. Does the test light flash ON and then OFF? If yes, go to step 18 . If no, go to step 15 .
13. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Turn ignition on, with engine off. Probe the TAC motor control 1 and 2 circuits with the test light connected to ground. Does the test light illuminate? If yes, go to step 20 . If no, go to step 19 .
14. Turn ignition off. Disconnect the PCM connector that contains the TAC motor control circuits. Probe the TAC motor control 1 and 2 circuits with the test light connected to battery positive. Does the test light illuminate? If yes, go to step 21 . If no, go to step 19 .
15. Turn ignition off. Disconnect the PCM connector that contains the TAC motor controls circuits. Test TAC motor control 1 and 2 circuits for an open or high resistance. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 19 .
16. Test the ETC/TAC ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to next step.
17. Test the motor control 1 circuit for a short to ground. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
18. Test for a poor connection or terminal tension at the throttle body connector. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
19. Test for a poor connection or terminal tension at the PCM. Did you find and correct the condition? If yes, go to step 26 . If no, go to step 24 .
20. Repair short to voltage on the circuit where the test light remained illuminated. After repairs, go to step 26 .
21. Repair short to ground on the circuit where the test light remained illuminated. After repairs, go to step 26 .
22. Repair short to voltage on the ETC ignition 1 voltage circuit. After repairs, go to step 26 .
23. Repair open or high resistance in the ETC ignition 1 voltage circuit. After repairs, go to step 26 .
24. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 26 .
25. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
26. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S18668387192003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
27. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The throttle valve is spring loaded to a slightly open position. The throttle valve should be open about 20 percent. This is referred to as the rest position. The throttle valve should not be completely closed nor should they be open any more than the specified amount. The throttle valve should move open and to the closed position without binding under the normal spring pressure. The throttle should NOT be free to move open or closed WITHOUT spring pressure. Replace throttle body if any of these conditions are found. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

Note. Operating the throttle blade with the Throttle Blade Control function of scan tool may cause additional DTCs to set. Do not attempt to diagnose DTCs set during this function.

The scan tool has the ability to operate the throttle control system using Special Functions. Actuate the throttle valve using the throttle blade control function located in the TAC System menu. This function will operate the throttle valve through the entire range in order to determine if the throttle body and system operate correctly. Check for the following conditions

1. Use the Connector Test Adapter Kit (J-35616-A) for any test that requires probing the PCM harness connector or a component harness connector.
2. Poor connections at the PCM or at the component. Inspect the harness connectors for a poor terminal to wire connection.
3. If the condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

1. Ignition is ON and the engine is OFF.
2. Ignition voltage is more than 8.5 volts.
3. Battery Saver Mode is active.

PCM detects that the commanded and actual throttle positions are not within a calibrated range of each other.

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

1. The DTC becomes history when the conditions for setting the DTC are no longer present.
2. The history DTC clears after 40 malfunction free warm-up cycles.
3. PCM receives a clear code command from scan tool.

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Are any other DTCs set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
3. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Allow the pedal to rest at idle stop for 20 seconds. With scan tool, observe the indicated throttle position parameter. Does scan tool indicate throttle position of 10.8-23.2 percent? If yes, go to step 6 . If no, go to next step.
4. Remove throttle body assembly. Did you find any obstructions preventing the throttle blade from returning to the default position? If yes, go to next step. If no, go to step 6 .
5. Remove obstruction. After repairs, go to step 7 .
6. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to next step.
7. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
8. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

If you do not find any trouble, inspect for mechanical conditions or binding that may be temperature related. Components may not move freely in extreme heat or cold due to the presence of contaminants or ice formation.

There is no Class II serial data circuit condition.

The ignition 1 voltage is present but ignition zero is not.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Does the engine run with the ignition OFF? If yes, go to step 6 . If no, go to next step.
3. Are DTCs P0740, P0753, P0785, or P1860 also set? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, go to next step.
4. Turn ignition off. Disconnect the PCM. Connect a test light between the ignition 0 voltage circuit and a good ground. Turn ignition on, with engine off. Does the test light illuminate? If yes, go to step 9 . If no, go to next step.
5. Test the ignition 0 voltage circuit for an open between the splice and the PCM. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
6. Disconnect the PCM. Test both ignition 1 voltage circuits for a short to voltage. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
7. Test for an intermittent and for poor connection at the PCM. Did you find and correct the condition? If yes, go to step 9 . If no, go to next step.
8. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
9. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S32767854272003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
10. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The ignition is ON.

1. PCM detects a voltage that is higher or lower than required on the 5-volt reference circuit.
2. Condition present for longer than 10 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
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 DTC or as close as possible to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S36164881252003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Turn ignition off. Disconnect the throttle body electrical connector. Turn ignition on, with engine off. Measure the voltage from the 5-volt reference "A" circuit of the Throttle Position (TP) sensor 1 to a good ground with a DVOM. Is the voltage about 5 volts? If yes, go to step 5 . If no, go to next step.
4. Is the voltage more than 5 volts? If yes, go to step 8 . If no, go to step 6 .
5. Connect the throttle body electrical connector. Disconnect the AC pressure sensor. Measure the voltage from the 5-volt reference circuit of the AC pressure sensor to a good ground with a DVOM. Is the voltage about 5 volts? If yes, go to step 10 . If no, go to step 9 .
6. Monitor the DVOM while disconnecting all other devices connected to the 5-volt reference "A" circuit one at a time. If voltage changes when one of the components are disconnected, replace component. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Was a component replaced? If yes, go to step 12 . If no, go to next step.
7. Turn ignition off. Disconnect PCM. Test the 5-volt reference "A" circuit for a short to ground or for any sensor low reference circuit. If a condition is found, repair as necessary. Did you find and correct a condition? If yes, go to step 12 . If no, go to step 10 .
8. Turn ignition on, with engine off. Test the following circuits for a short to voltage: The 5-volt reference "A" circuit. The FTP sensor signal circuit. If a condition is found, repair as necessary. Did you find and correct a condition? If yes, go to step 12 . If no, go to step 10 .
9. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 12 .
10. Test the 5-volt reference "A" circuit for a short to the TAC motor control 1 or 2 circuits. Did you find and correct a condition? If yes, go to step 12 . If no, go to next step.
11. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
12. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S36164881252003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
13. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The ignition is ON.

1. The PCM detects a voltage that is higher or lower than required on the 5-volt reference circuit.
2. Condition present for longer than 10 seconds.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
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 DTC or as close as possible to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S39951077502003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Turn ignition off. Disconnect the throttle body electrical connector. Turn ignition on, with engine off. Measure the voltage from the 5-volt reference "B" circuit of the Throttle Position (TP) sensor 2 to a good ground with a DVOM. Is the voltage about 5 volts? If yes, go to step 5 . If no, go to next step.
4. Is the voltage more than 5 volts? If yes, go to step 8 . If no, go to step 6 .
5. Connect the throttle body electrical connector. Disconnect the MAP sensor. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DVOM. Is the voltage about 5 volts? If yes, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no, go to step 9 .
6. Monitor the DVOM while disconnecting all other devices connected to the 5-volt reference "B" circuit one at a time. If voltage changes when one of the components are disconnected, replace component. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Was a component replaced? If yes, go to step 12 . If no, go to next step.
7. Turn ignition off. Disconnect the PCM. Test the 5-volt reference "B" circuit for a short to ground or for any sensor low reference circuit. If a condition is found, repair as necessary. Did you find and correct a condition? If yes, go to step 12 . If no, go to step 10 .
8. Turn ignition on, with engine off. Test the following circuits for a short to voltage: The 5-volt reference "B" circuit. The MAP sensor signal circuit. If a condition is found, repair as necessary. Did you find and correct a condition? If yes, go to step 12 . If no, go to step 10 .
9. Replace throttle body assembly. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After repairs, go to step 12 .
10. Test the 5-volt reference "B" circuit for a short to the TAC motor control 1 or 2 circuits. Did you find and correct a condition? If yes, go to step 12 . If no, go to next step.
11. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
12. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S39951077502003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
13. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.

The ignition is ON.

The ignition 1 voltage is less than 10 volts.

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

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

1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition on, with engine off. With scan tool, command the throttle blade to 100 percent and back to zero percent. Exit the throttle blade control function. Did the throttle blade angle follow the commanded angle? If yes, go to next step. If no, go to step 4 .
3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S02582823052003062800000) . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. With a test light connected to ground, probe both sides of the ETC fuse. Does the test light illuminate on both sides of the fuse? If yes, go to next step. If no, go to step 6 .
5. With a test light connected to ground, probe both sides of the PCM fuse. Does the test light illuminate on both sides of the fuse? If yes, go to step 10 . If no, go to step 8 .
6. Test the ETC ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
7. Test the supply voltage to the ETC fuse for an open or high resistance. If a short to ground is found, replace affected fuse. Did you find and correct the condition? If yes, go to step 16 . If no, go to step 10 .
8. Test the PCM ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
9. Test the supply voltage to the PCM fuse for an open or high resistance. If a short to ground is found, replace the affected fuse. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
10. Disconnect the PCM connector containing the ETC ignition 1 voltage. With a DVOM connected to ground, measure the voltage on the ETC ignition 1 voltage circuit. Does the voltage measure about 12 volts? If yes, go to next step. If no, go to step 12 .
11. Disconnect the PCM connector containing the PCM ignition 1 voltage. With a DVOM connected to ground, measure the voltage on the PCM ignition 1 voltage circuit. Does the voltage measure about 12 volts? If yes, go to step 14 . If no, go to step 13 .
12. Test the ETC ignition 1 voltage circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
13. Test the PCM ignition 1 voltage circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
14. Test for poor connections at the PCM connectors. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
15. Replace PCM. See «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. Reprogram PCM. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING. After repairs, go to next step.
16. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See «CONDITIONS FOR RUNNING DTC»(ref-155898-S02582823052003062800000) . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
17. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . If no, system is okay.