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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 379 (Engine Controls Self-Diagnostics - 3.4L) >> Diagnostic Tests >> DTC P0300-P0306: Engine Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
    2. NOTE: You MUST perform the Crankshaft Position (CKP) system variation learn procedure before proceeding with this diagnostic procedure. See CKP SYSTEM VARIATION LEARN PROCEDURE  under PROGRAMMING.
  2. Start the engine. Allow engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. Monitor all of the Misfire counters using the scan tool. Are any of the Misfire Current counters incrementing? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  3. Are any other DTCs set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  4. Can any abnormal engine noise be heard? If yes, diagnose engine mechanical problem. See appropriate article in ENGINES. If no, go to next step.
  5. Observe the MISFIRE HISTORY CYL NO. parameter using a scan tool. Does more than one cylinder indicate a large count value for the MISFIRE HISTORY CYL NO. parameter? If yes, go to next step. If no, go to step  8.
  6. Are the Misfire History Cyl No. counts indicated for companion cylinders 1/4 or 2/5 or 3/6? If yes, go to step  8. If no, go to next step.
  7. Inspect the following components:
    • The vacuum hoses and seals for splits, restrictions, and improper connections.
    • The throttle body and intake manifold for vacuum leaks.
    • The crankcase ventilation system for vacuum leaks.
    • The Exhaust Gas Recirculation (EGR) system components for vacuum leaks or excessive flow. See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS & SUBSYSTEMS in SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
    • The PCM grounds for corrosion and loose connections.
    • The exhaust system for restrictions. See EXHAUST SYSTEM in SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
    • The fuel for contamination. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.

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

  8. Turn ignition switch to OFF position. Disconnect the spark plug wire from the spark plug that corresponds to the Misfire Current counters that were incrementing. Install the Spark Tester (J 26792), or equivalent, to a good ground. Jumper the spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil. Start the engine. Does the spark jump the tester gap, and is the spark consistent? If yes, go to step  10. If no, go to next step.
  9. Remove the spark plug wire for the affected cylinder. Inspect the spark plug wire. Measure the resistance of the spark plug wire using a DMM. Is the spark plug wire resistance less than 700 ohms? If yes, go to ELECTRONIC IGNITION SYSTEM DIAGNOSIS under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article. If no, go to step  19.
  10. Remove the spark plug from the cylinder that indicated a misfire. Inspect the spark plug. Does the spark plug appear to be okay? If yes, go to next step. If no, go to step  12.
  11. Exchange the suspected spark plug with another cylinder that is operating properly. Operate the vehicle under the same conditions that the misfire occurred. Did the misfire move with the spark plug? If yes, go to step  18. If no, go to step  15.
  12. Is the spark plug oil or coolant fouled? If yes, diagnose engine mechanical problem. See appropriate article in ENGINES. If no, go to next step.
  13. Is the spark plug gas fouled? If yes, go to step. If no, go to step  16. If no, go to next step.
  14. Does the spark plug show any signs of being cracked, worn, or improperly gapped? If yes, go to step  17. If no, go to next step.
  15. Perform the fuel injector coil test. See FUEL INJECTOR COIL TEST under FUEL SYSTEMS - SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
  16. Perform the fuel system diagnosis. Go to FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS - SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
  17. Replace or gap the spark plug. After repair, go to step  20.
  18. Replace the faulty spark plug. After repair, go to step  20.
  19. Replace the faulty spark plug wires. After repair, go to step  20.
  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 as specified in the supporting text. See CONDITIONS FOR RUNNING  in DTC P0420: TWC SYSTEM - LOW EFFICIENCY. Does the DTC run and pass? If yes, go to next step. If no, see DTC P0420: TWC SYSTEM - LOW EFFICIENCY .
  22. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running. See CONDITIONS FOR RUNNING . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  23. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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