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Home >> Pontiac >> 2003 >> Aztek FWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0300-P0306: Engine Misfire Detected >> Diagnostic Procedures
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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 CKP system variation learn procedure before proceeding with this diagnostic test. See CRANKSHAFT POSITION SENSOR  under PROGRAMMING.
  2. Start engine. Allow the engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. Monitor all of the Misfire Current 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, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  4. Can any abnormal engine noise be heard? If yes, diagnose for an engine mechanical problem. If no, go to next step.
  5. Observe the Misfire History Cyl# parameter with a scan tool. Does more than one cylinder indicate a large count value for the Misfire History Cyl# parameter? If yes, go to next step. If no, go to step  8.
  6. Are the Misfire History Cyl# 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 vacuum hoses and seals for splits, restrictions, and improper connections. Inspect throttle body and intake manifold for vacuum leaks, crankcase ventilation system for vacuum leaks, or EGR system components for vacuum leaks or excessive flow. Inspect PCM grounds for corrosion and loose connections, exhaust for restrictions, or fuel for 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 Spark Tester (J-26792) 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 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 with a DVOM. Is the spark plug wire resistance less than 700 ohms? If yes, diagnose Electronic Ignition (EI) system. Refer to ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.4L AZTEK & RENDEZVOUS 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 next step.
  12. Is the spark plug oil or coolant fouled? If yes, diagnose for an engine mechanical problem. If no, go to next step.
  13. Is the spark plug gas fouled? If yes, 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. Did you find and correct the condition? If yes, go to step  20. If no, diagnose for an engine mechanical problem.
  16. Perform the fuel system diagnosis. Did you find and correct the condition? If yes, go to step  20. If no, diagnose for an engine mechanical problem.
  17. Replace or gap the spark plug. After regapping or replacing spark plugs, go to step  20.
  18. Replace faulty spark plug. After replacing spark plug, go to step  20.
  19. Replace faulty spark plug wires. After replacing spark plug wires, go to next step.
  20. Was the customer's concern regarding the MIL flashing? If yes, go to next step. If no, go to step  22.
  21. Operate engine at 2500 RPM for 4 minutes. Operate the vehicle within the Conditions for Running this DTC or DTC P0420. Does the DTC run and pass? If yes, go to next step. If no, go to DTC P0420: TWC SYSTEM - LOW EFFICIENCY .
  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. 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.
  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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