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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 433 (Engine Controls - Self-Diagnostics - 6.0L Bi-Fuel & CNG) >> Diagnostic Tests >> DTC P0300-P0308: Engine Misfire Detected >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Alternative Fuels - Engine Controls. If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ignition on, with engine off. Using a scan tool, observe the DTC information. If any other DTCs are set, g to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  3. Start the engine. Using a scan tool, clear the DTCs. Allow the engine to reach operating temperature. Observe the Misfire Current Counters using a scan tool. If any of the misfire current counters are incrementing, go to step  7. If none of the misfire current counters are incrementing, go to next step.
  4. If the vehicle is equipped with the Bi-Fuel option (KL6), go to next step. If vehicle is not equipped with the Bi-Fuel option (KL6), go to step  6.
  5. Using the scan tool output controls function, force a switch over to gasoline. Using a scan tool, observe the Misfire Current Counters. If any of the Misfire Current Counters are incrementing, see DTC P0200: INJECTOR CONTROL CIRCUIT VOLTAGE , If none of the Misfire Current Counters are incrementing, go to next step.
  6. Observe the Freeze Frame and the Failure records data for this DTC. Turn ignition off 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, and the Failure Records data. If the DTC failed this ignition cycle, go to next step. If the DTC does not fail this ignition cycle, see DIAGNOSTIC AIDS .
  7. If the engine is misfiring, go to step  9. If the engine is not misfiring, go to next step.
  8. Perform the Crankshaft Variation Learn Procedure. See CKP SYSTEM VARIATION LEARN PROCEDURE under PROGRAMMING in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article. Start the engine. Using a scan tool, observe the Misfire Current Counters. If any of the Misfire Current Counters are incrementing, see appropriate article in ENGINES. If none of the Misfire Current Counters are incrementing, go to step  21.
  9. Using a scan tool, observe the Misfire Current Counters. Is there only one Misfire Current Counter incrementing? If yes, go to next step. If no, go to step  16.
  10. Turn ignition off. Disconnect the spark plug wire from the spark plug that indicates a misfire. Connect the Spark Tester to the spark plug wire and a good ground. Start and idle the engine. If the Spark Tester sparks and is the spark consistent go to step  12. If the Spark Tester does not spark or spark is not consistent, go to next step.
  11. Turn ignition off. Remove the spark plug wire from the cylinder that indicates a misfire. Measure the resistance of the spark plug wire with a DVOM. If the resistance is less than 625 ohms per 12" (per 30 cm), see ELECTRONIC IGNITION SYSTEM DIAGNOSIS under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - GASOLINE article. If the resistance is more than 625 ohms per 12" (per 30 cm), go to step  18.
    12. NOTE: If the spark plug is gas, coolant, or oil fouled, determine the cause of the fouling. See DTC P0172: FUEL TRIM SYSTEM RICH - BANK 1 & DTC P0175: FUEL TRIM SYSTEM RICH - BANK 2 under DIAGNOSTIC TEST in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article, or see appropriate article in ENGINES for spark plugs that are coolant or oil fouled.
  12. Remove the spark plug from the cylinder that indicates a misfire. Inspect the spark plug. If you found and corrected a misfire condition, go to step  19. If you did not find and correct a misfire condition, go to next step.
  13. Swap the suspected spark plug with another cylinder that is operating correctly. Start the engine. Operate the engine within the conditions that the misfire occurred. Using a scan tool, monitor the misfire current counters. If the misfire moved with the spark plug, go to step  17. If the misfire did not move with the spark plug, go to next step.
    14. NOTE: Make sure all the injectors operate. High resistance in an injector circuit causes the injector to be inoperative without setting a fuel injector DTC. Return to this diagnostic after you complete the Fuel Injector Coil Test.
  14. Perform the Fuel Injector Coil Test. See FUEL INJECTOR COIL TEST under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article. Did you find and correct the condition performing fuel injector coil test? If yes, go to step  19. If no, go to next step.
  15. Perform the Fuel System Diagnosis. see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article. Did you find and correct a fuel system condition? If yes, go to step  19. If no, see appropriate article in ENGINES.
  16. Inspect or test for the following conditions:
    • Vacuum hoses for splits, kinks, and the correct connections.
    • Vacuum leaks at the throttle body and at the intake manifold.
    • PCM grounds for being clean, tight, and in the correct location.
    • Correct fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.
    • Faulty spark plug wires.
    • Fouled or damaged spark plugs.
    • Exhaust system for restrictions. See RESTRICTED EXHAUST under SYMPTOMS in TROUBLE SHOOTING - NO CODES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.

    Did you find and correct the condition? If yes, go to step  19. If no, see appropriate article in ENGINES.

  17. Replace the spark plug. After replacement is complete, go to step  19.
  18. Replace the spark plug wire. After replacement is complete, go to next step.
  19. If the customers concern was a flashing MIL, go to next step. If the customers concern was not a flashing MIL, go to step  21.
  20. 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. See DTC P0420: TWC SYSTEM - LOW EFFICIENCY - BANK 1 & DTC P0430: TWC SYSTEM - LOW EFFICIENCY - BANK 2 under DIAGNOSTIC TEST in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article. If the DTC did not fail this ignition cycle, go to next step. If the DTC failed this ignition cycle, see DTC P0420: TWC SYSTEM - LOW EFFICIENCY - BANK 1 & DTC P0430: TWC SYSTEM - LOW EFFICIENCY - BANK 2 under DIAGNOSTIC TEST in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article.
  21. Using a scan tool, clear the DTCs. Turn the ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running The DTC. If the DTC did not fail this ignition cycle, go next step. If DTC failed this ignition cycle, go to step  2.
  22. Observe the Capture Info using 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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