Basic Diagnostic Procedure
NOTE:
Most computerized engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. 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 computerized engine control system should be performed in the following order:
- Make sure that all engine systems not related to the computer system are operating properly. Do not proceed with testing unless all other problems have been repaired.
- 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 DEFINITIONS table in the 3.3/3.8L PFI TESTS/CODES article in this section.
- If no trouble codes were displayed, perform FIELD SERVICE MODE CHECK procedures.
- If no trouble is indicated by the FIELD SERVICE MODE check and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS and/or SCAN TESTER USAGE in the TROUBLE SHOOTING procedures in the CCC TESTS W/O CODES article in this section. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
- After any repairs are made, clear any trouble codes and perform FIELD SERVICE MODE check again.