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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 54 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0301-P0306: Engine Misfire Detected In Cylinder No. 1-6 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
  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. Check for other DTCs that may cause a misfire. Did you find any other DTCs? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, go to next step.
  3. Connect the scan tool. Start the engine. Allow the engine to idle or operate within the conditions listed in the Freeze Frame records. Using the scan tool, monitor the Misfire Current Counter for this cylinder. Is the Misfire Current Counter incrementing? If yes, go to next step. If no, see DIAGNOSTIC AIDS  .
  4. Inspect the following items:
    • The vacuum hoses for splits, kinks and proper connections.
    • The throttle body and the intake manifold for vacuum leaks.
    • The crankcase ventilation valve and/or system for vacuum leaks.
    • Ensure that the PCM grounds are clean and secure.

    Did you find and correct the condition? If yes, go to step  8 . If no, go to next step.

  5. Perform the Fuel Injector Balance Test and the Fuel Injector Coil Test on the affected cylinder. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. Did you find and correct the condition? If yes, go to step  8 . If no, go to next step.
  6. Perform the Ignition System Check on the affected cylinder. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. Did you find and correct the condition? If yes, go to step  8 . If no, go to next step.
  7. Turn OFF the ignition. Disconnect the HO2S 1 connector. Start the engine and allow the engine to idle. Using the scan tool, monitor the Misfire Current Counter for this cylinder. Is the Misfire Current Counter incrementing? If yes, see appropriate article in ENGINES. If no, see DTC P0130: CLOSED LOOP RATIONALITY  .
  8. 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 DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2 .
  9. 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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