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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 385 (Engine Controls Self-Diagnostics) >> Diagnostic Tests >> DTC P0300-P0308: Engine Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  1. 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.
    2. NOTE: You must perform the Crankshaft Position (CKP) system variation learn procedure before proceeding with this diagnostic procedure.
  2. Start the engine and allow the 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 current misfire counters incrementing? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  3. Are any DTCs other than P0300, P0135 or P0155 set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  4. Can any abnormal engine noise be heard? If yes, see appropriate article in ENGINES. If no, go to next step.
  5. Does the scan tool indicate HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are below 200 mV? If yes, see DTC P0131 & P0151: HO2S CIRCUIT - LOW VOLTAGE - BANK 1 & 2, SENSOR 1 . If no, go to next step.
  6. Does the scan tool indicate HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are fixed above 900 mV? If yes, see DTC P0132 & P0152: HO2S CIRCUIT - HIGH VOLTAGE - BANK 1 & 2, SENSOR 1 . If no, go to next step.
  7. Inspect the following items:
    • Inspect vacuum hoses for splits, kinks, and correct connections.
    • Inspect throttle body and intake manifold for vacuum leaks.
    • Inspect crankcase ventilation system for any vacuum leaks.
    • Verify PCM grounds are clean and secure.
    • Inspect for a restricted exhaust.
    • Test for fuel contamination.

    Did you find and correct the condition? If yes, go to step  20. If no, go to next step.

  8. Turn ignition OFF. Disconnect the spark plug wire from the spark plug that corresponds to the Misfire Current counters that were incrementing. Install the Spark Tester to a good ground. Start the engine. Does the spark jump the Spark Tester gap, and is the spark consistent? If yes, go to step  10. If no, go to next step.
  9. Remove the spark plug wire for the affected cylinder. Inspect the spark plug wire. Measure the resistance of the spark plug wire. Is the spark plug wire resistance less than 700 ohms? If yes, see IGNITION SYSTEMS in SERVICE & ADJUSTMENT SPECIFICATIONS - CORVETTE article. If no, go to step  19.
  10. Remove spark plug from the cylinders that indicated a misfire and inspect. Does spark plug appear to be OK? If yes, go to next step. If no, go to step  12.
  11. Switch suspected spark plug with a spark plug from another cylinder that is operating properly. Operate the vehicle under the same conditions that the misfire occurred. Did the misfire move with the spark plug? If yes, go to step  18. If no, go to step  15.
  12. Are the spark plugs oil fouled or coolant fouled? If yes, check engine mechanical condition. See appropriate article in ENGINES. If no, go to next step.
  13. Are the spark plugs gas fouled? If yes, go to step  16. If no, go to next step.
  14. Do the spark plugs show any signs of being cracked, worn, or improperly gapped? If yes, go to step  17. If no, go to next step.
  15. Perform the fuel injector coil test. See appropriate SYSTEM & COMPONENT TESTING article. Did you find and correct the condition? If yes, go to step  20. If no, check engine mechanical condition. See appropriate article in ENGINES.
  16. Perform the fuel system diagnosis. See appropriate SYSTEM & COMPONENT TESTING article. Did you find and correct the condition? If yes, go to step  20. If no, check engine mechanical condition. See appropriate article in ENGINES.
  17. Replace or re-gap the spark plugs. If an improper gap is found, use a wire-type gauge to re-gap the spark plugs. Did you find and correct the condition? If yes, go to step  20.
  18. Replace faulty spark plug. Did you complete the replacement? If yes, go to step  20.
  19. Replace faulty spark plug wire. Did you complete the replacement? If yes, go to next step.
  20. Was the customer concern the MIL flashing? If yes, go to next step. If no, go to step  22.
  21. Operate the vehicle at 2500 RPM for 4 minutes. Operate the vehicle within the Conditions for Running the DTC P0420 or P0430 as specified in the supporting text. Does the DTC run and pass? If yes, go to next step. If no, see DTC P0420 & P0430: TWC SYSTEM - LOW EFFICIENCY - BANK 1 & 2 .
  22. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the 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 cycle? If yes, go to step  2. If no, go to next step.
  23. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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