LEMON Manuals: Even more car manuals for everyone
Home >> Oldsmobile >> 2003 >> Bravada AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Self-Diagnostics - 4.2L >> Diagnostic Tests >> DTC P0300: Random/Multiple Cylinder Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

  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 test. Refer to CRANKSHAFT POSITION SENSOR  under PROGRAMMING.
  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 .
  3. Are any other DTCs set? If yes, diagnose affected DTC(s) first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . 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 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 . 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) .
  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 . 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 . If no, system is okay.
scientia non olet · About LEMON Manuals