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. On-Board Diagnostic (OBD) system check must be performed before using specific DTC testing procedure. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  .
2. If DTCs were displayed, determine whether DTCs are hard or intermittent. Hard DTCs will cause MIL to illuminate continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION  . For diagnosing hard DTCs, proceed to appropriate DTC test. See DIAGNOSTIC TESTS. For diagnosing intermittent DTCs, see appropriate TROUBLE SHOOTING - NO CODES article.
3. If no DTCs are present and a driveability problem exists, refer to SYMPTOMS in appropriate TROUBLE SHOOTING - NO CODES article. Doing so will help identify proper system or component to check in appropriate SYSTEM & COMPONENT TESTING article.
4. After necessary repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation and ensure DTC does not reset.