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Home >> Pontiac >> 2001 >> Aztek Base, AWD >> 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. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. If are any other DTCs are set, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  3. Start and operate engine at idle. Using scan tool, review and record scan tool FREEZE FRAME data. Operate vehicle to duplicate the conditions present when DTC was set (as defined by FREEZE FRAME data. Monitor Misfire Current Cyl # display for each cylinder. If Misfire Current # display is incrementing for any cylinder, indicating a misfire currently occurring, go to step  5. If Misfire Current # display is not incrementing for any cylinder, go to next step.
  4. View Misfire History Cyl # display on scan tool. If Misfire History Cyl # displays a very large value for more than one cylinder, go to next step. If Misfire History Cyl # does not display a very large value for more than one cylinder, go to step  8.
  5. If misfire values displayed on the Misfire History Cyl # is related to the companion cylinders (i.e. 1/4, 2/5, 3/6), go to step  9. If misfire values displayed on the Misfire History Cyl # is not related to the companion cylinders, go to next step.
  6. Check for excessive vibration from sources other than the engine. Check vacuum hoses and crankcase ventilation system for vacuum leaks. Check throttle body and intake manifold for vacuum leaks. Check PCM grounds, spark plug wires, EGR valve to exhaust manifold pipe for proper connections and signs of damage. For PCM grounds, see WIRING DIAGRAMS article. Check for fuel contamination. Repair as necessary. After repairs, go to step  18. If no problem is found, go to next step.
  7. Install fuel pressure gauge. Turn ignition on, with engine off. Using scan tool, command fuel pump on. Monitor fuel pressure with fuel pump running. If fuel pressure is 52-59 psi (358-405 kPa), go to next step. If fuel pressure is not 52-59 psi (358-405 kPa), diagnose fuel system. See BASIC FUEL SYSTEM CHECKS (GASOLINE) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Check fuel injector. See appropriate FUEL SYSTEM (GASOLINE) in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step  18. If no problem is found, go to next step.
  9. Check ignition wires and coils associated with misfiring cylinders for carbon tracking/arching and damage. Check for incorrect connection to cylinders at coil and spark plug. Check for poor terminal connections at coil and spark plug. Repair as necessary. After repairs, go to step  18. If no problem is found, go to next step.
  10. Install Spark Tester (J-26792) at spark plug end of ignition wire associated with the misfiring cylinders. Jumper spark plug end of the companion cylinder ignition wire to engine ground (i.e. 1/4, 2/5, 3/6). Crank engine while observing spark tester. If spark is present, go to step  15. If no spark is present, go to next step.
  11. Check resistance of ignition wires associated with cylinders that were indicated as misfiring. Resistance should be greater than 3000 ohms per foot. Replace as necessary. After replacing wires, go to step  18. If wires are okay, go to next step.
  12. Check resistance of secondary ignition coils associated with the misfiring cylinders. Resistance should be 5000-8000 ohms. Replace as necessary. After replacing ignition coil(s), go to step  18. If ignition coil(s) are okay, go to next step.
  13. Remove ignition coils associated with the misfiring cylinders. Check coils for signs of carbon tracking, cracks or other damage. Repair as necessary. After repairs, go to step  18. If ignition coils are okay, go to next step.
  14. Leave ignition coils disconnected. Connect a test light across the ignition module primary circuit terminals. Remove fuel injector fuse (located in underhood fuse/relay block). Observe test light while cranking engine. If test light blinks, go to step  16. If test light does not blink, go to step  17.
  15. Remove and check spark plug from cylinders associated with the misfire. Replace as necessary. After replacing spark plugs, go to step  18.
  16. Reinstall fuel injector fuse. Replace ignition coil(s) associated with misfiring cylinders. After replacing ignition coil(s), go to step  18.
  17. Reinstall fuel injector fuse. Replace ignition coil(s) associated with misfiring cylinders. After replacing ignition coil(s), go to next step.
  18. Review and record FREEZE FRAME data. Clear DTCs. Operate vehicle to duplicate the conditions present when DTC was set, as defined by FREEZE FRAME data. Monitor the scan tool Misfire Current Cyl # display for each cylinder. If Misfire Current Cyl # display is incrementing for any cylinder (indicating a misfire currently occurring), diagnose for a mechanical engine problem. If Misfire Current Cyl # display is not incrementing, system is okay.
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