Diagnostic Procedure

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

1. Ensure all engine systems not related to computer are operating properly. Check for any Technical Service Bulletins (TSB) that may apply. DO NOT proceed with testing unless all other problems have been repaired. Perform OBD system check before diagnosing Diagnostic Trouble Codes (DTC). See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
2. If DTC 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, perform appropriate DTC test. See DIAGNOSTIC TESTS . For diagnosing intermittent DTCs, see INTERMITTENTS in appropriate TROUBLE SHOOTING - NO CODES article.
3. If no DTCs are set and a driveability problem exists, see SYMPTOMS in appropriate TROUBLE SHOOTING - NO CODES article. Doing so will help identify proper system or component to check. See appropriate SYSTEM & COMPONENT TESTING article for diagnosis of faulty component.
4. After necessary repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation, and ensure no DTCs set.