Diagnostic Procedure

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

1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. Basic diagnostic procedure must be performed before using specific DTC testing procedure. See BASIC DIAGNOSTIC PROCEDURE  .
2. If DTCs were displayed, determine whether codes are hard or intermittent. Hard codes will cause MIL to illuminate continuously while engine is running. See HARD FAILURES  and INTERMITTENT FAILURES  . For diagnosing hard codes, proceed to appropriate DTC test. See DIAGNOSTIC TESTS  . For diagnosing intermittent codes, see TROUBLE SHOOTING - NO CODES article.
3. If no DTCs are present and a driveability problem exists, refer to SYMPTOMS in TROUBLE SHOOTING - NO CODES article. Doing so will help identify proper system or component to check in SYSTEM & COMPONENT TESTING article.
4. After necessary repairs are made, clear DTCs, and perform verification of repair to ensure DTC does not reset.