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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ensure fuel level is more than 1.6 gallons. Operate engine for one minute. Using scan tool, monitor current misfire counters. If any current counters are incrementing, go to next step. If no current counters are incrementing, problem is intermittent. Review MISFIRE HISTORY to see which cylinders where misfiring. See DIAGNOSTIC AIDS  .
  2. If a particular counter is dominant, see DTC P0301-P0306: SPECIFIC CYLINDER MISFIRE DETECTED  . If a particular counter is not dominant, go to next step.
  3. If misfire counters from both banks are randomly filling up, go to next step. If misfire counters from one bank are dominate, go to step  5 . If only 2 cylinders on one bank are dominate, a mechanical failure may exist. Perform a compression test.
  4. Check the following for possible causes of random cylinder misfires:
    • Large vacuum leak.
    • Fuel pressure too low. Should be 50-60 psi.
    • Fuel quality poor. Water will separate in test sample.
    • Clogged fuel injectors. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.
    • Spark plug boots arcing beneath EI module.
    • Timing belt incorrectly timed or exhaust valves sticking.
    • Main converter or exhaust restricted.
  5. Ignition on, engine off. Using Scan tool, perform ignition coil cyl. No. 1-6 test on each individual cylinder that was misfiring, while listening for audible spark at each cylinder. See appropriate SYSTEM & COMPONENT TESTING article. If spark is not audible on at least one cylinder, go to next step. If spark is audible on at least one cylinder, the cam timing for the bank that was misfiring may be incorrectly timed or the pre-converter for the same bank may be restricted.
  6. Disconnect El module from the bank of cylinders that were misfiring. Connect test light between EI harness connector terminals No. 1 (Black/White wire) and No. 2 (Pink wire). If test light is on, check connector. If connector is okay, replace EI module. If test light is off, repair open in Pink wire or Black/White wire.
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