Diagnostic Procedure

Diagnosis of the computerized engine control system should be performed in the following order:

1. Ensure all engine systems not related to the computer are operating properly. DO NOT proceed with testing unless all other problems have been repaired. Perform on-board diagnostic system check chart before using trouble code charts.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent. Hard codes cause Malfunction Indicator Light (MIL) to illuminate continuously with engine running. For diagnosing hard codes, proceed to appropriate diagnostic code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
3. If trouble codes were not displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section. From there you will be sent to the appropriate area in I - SYS/COMP TESTS article.
4. After repairs are made, clear trouble codes, confirm closed loop operation and ensure MIL is not illuminated.