LEMON Manuals: Even more car manuals for everyone
Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P0300-P0306: Engine 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: Perform the Crankshaft Position (CKP) system variation learn procedure before proceeding with this diagnostic test. Refer to CRANKSHAFT POSITION SENSOR  Learn Procedure 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 Counters with 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, diagnose affected DTCs. Go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  table. 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. Does the scan tool indicate that the HO2S bank 1, sensor 1 or HO2S bank 2, sensor 1 voltage parameters are less than 200 mV? If yes, go to DTC P0131 OR P0151: HO2S CIRCUIT - LOW VOLTAGE (BANK 1 & 2, SENSOR 1) . If no, go to next step.
  6. Does the scan tool indicate that the HO2S bank 1, sensor 1 or HO2S bank 2, sensor 1 voltage parameters are fixed greater than 900 mV? If yes, go to DTC P0132 OR P0152: HO2S CIRCUIT - HIGH VOLTAGE (BANK 1 & 2, SENSOR 1) . 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, PCM grounds for corrosion and loose connections, 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 counter that was incrementing. Install Spark Tester (J-26792) to a good ground. 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 spark plug wire. Measure resistance of the spark plug wire with a DVOM. Is the spark plug wire resistance less than 1000 ohms per foot? If yes, go to step  15. If no, go to step  20.
  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  19. If no, go to step  16.
  12. Are the spark plugs oil or coolant fouled? If yes, diagnose for an engine mechanical problem. If no, go to next step.
  13. Are the spark plugs gas fouled? If yes, go to step  17. 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  18. If no, go to step  16.
  15. Inspect the distributor cap and repair or replace as necessary. After repairs, go to step  21.
  16. Perform Fuel Injector Coil Test. See FUEL INJECTOR COIL TEST in SYSTEM & COMPONENT TESTING - 4.3L ASTRO, SAFARI, SONOMA & S10 PICKUP article. Did you find and correct the condition? If yes, go to step  23. If no, go to next step.
  17. Diagnose fuel system. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L ASTRO, SAFARI, SONOMA & S10 PICKUP article. Did you find and correct the condition? If yes, go to step  23. If no, check for mechanical engine problem. See appropriate article in ENGINES.
  18. Replace or gap spark plugs. After repairs, go to step  23.
  19. Replace spark plugs. After repairs, go to step  23.
  20. Replace spark plug wires. After repairs, go to next step.
  21. Was the customer's concern about the MIL flashing? If yes, go to next step. If no, go to step  23.
  22. Operate engine at 2500 RPM for 4 minutes. Operate the vehicle within the Conditions for Running the DTC P0420 or P0430. Refer to DTC P0420 OR P0430: TWC SYSTEM - LOW EFFICIENCY (BANK 1 & 2) . Does the DTC run and pass? If yes, go to next step. If no, go to DTC P0420 OR P0430: TWC SYSTEM - LOW EFFICIENCY (BANK 1 & 2) .
  23. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  24. Observe the stored information, Capture Info with a scan tool. Does the 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