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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 80 (Engine Controls Self-Diagnostics - 5.0L & 5,7L) >> Diagnostic Tests >> DTC P0300-P0308: Engine Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

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  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. Install the scan tool. Are any DTCs other than P0135 or P0155 stored? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Turn ON the ignition, with the engine OFF. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters. Turn OFF the ignition for 15 seconds. Start the engine. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running DTC. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, and then enter the DTC number using the scan tool. Does the scan tool indicate that this diagnostic failed this ignition cycle? If yes, go to step  5. If no, go to next step.
  4. Turn OFF the ignition. Use a spray bottle filled with water in order to wet down the secondary ignition system. Start the engine. Monitor the misfire counters in the misfire data list. Does the scan tool indicate a misfire is present? If yes, perform Electronic Ignition (EI) System Diagnosis. See appropriate SYSTEM & COMPONENT TESTING article. If no, go to step  13.
  5. Is the misfire random on all of the cylinders? If yes, go to step  10. If no, go to next step.
  6. Turn OFF the ignition. Connect the spark tester to the spark plug wire of the cylinders that indicate a misfire. Start and idle the engine. Does the tester indicate that the spark is consistent? If yes, go to next step. If no, perform Electronic Ignition (EI) System Diagnosis. See appropriate SYSTEM & COMPONENT TESTING article. If no, go to step  13.
  7. Remove the spark plugs from the cylinders that indicate a misfire. Inspect the spark plugs. Did you find and correct the condition? If yes, go to step  14. If no, go to next step.
  8. Install the spark plugs in the cylinders that did not indicate a misfire. Start the engine. Monitor the misfire counters in the misfire data list. Did the misfires change to other cylinders? If yes, go to step  12. If no, go to step  10.
  9. Perform the Fuel System Diagnostic. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. Did you find and correct the condition? If yes, go to step  16. If no, go to step  13.
  10. Perform the Fuel Injector Balance Test. See appropriate SYSTEM & COMPONENT TESTING article. Did you find a condition? If yes, go to step  15. If no, perform Fuel Injector Coil Test. See appropriate SYSTEM & COMPONENT TESTING article.
  11. Replace the spark plugs. After repairs, go to step  15.
  12. Check for the following conditions in the following order:
    • Contaminated fuel
    • Fouled or damaged spark plugs
    • The ignition coil and connections
    • The distributor cap for damage
    • The Exhaust Gas Recirculation (EGR) valve for leaks
    • The exhaust system for restrictions
    • The PCM grounds

    Repair any conditions as necessary. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.

  13. Perform the CKP System Variation Learn Procedure. See CRANKSHAFT POSITION SENSOR  under PROGRAMMING. When complete, go to next step.
  14. Check for engine mechanical problems. See appropriate article in ENGINES. Repair as necessary. Did you find and correct the condition? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  15. Select DTC, then select the Clear DTC Information function on the scan tool. Start the engine. Allow the engine to idle until the engine reaches the normal operating temperature. Select DTC, then select the Specific DTC function. Enter the DTC number which was set. Operate the vehicle within the Conditions for Setting this DTC until the scan tool indicates the diagnostic Ran. Does the scan tool indicate that the diagnostic Passed? If yes, go to next step. If no, go to step  2.
  16. 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.
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