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Basic Diagnostic Procedures

NOTE: Most computerized engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoes. Before considering the computer system as a possible cause of problems ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

Diagnosis of the CCC system should be performed in the following order:

  1. Make sure that all engine systems not related to the CCC system are operating properly. Do not proceed with testing unless all other problems have been repaired.
  2. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If trouble codes were displayed (other than Code 12), decide whether codes are "hard" or "intermittent" trouble codes. "Hard" codes will cause the "SERVICE ENGINE SOON" light to illuminate continuously while engine is running. See ECM TROUBLE CODE DEFINITION in this article.
  3. If no trouble codes were displayed, proceed to appropriate SYSTEM PERFORMANCE CHECK chart for carbureted systems or perform FIELD SERVICE MODE CHECK on fuel injected systems.
  4. If no trouble is indicated by SYSTEM PERFORMANCE CHECK or FIELD SERVICE MODE check and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS and/or SCAN TESTER USAGE TROUBLESHOOTING. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
  5. After any repairs have been made, clear any trouble codes and perform SYSTEM PERFORMANCE CHECK or FIELD SERVICE MODE check.
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