Diagnostic Flow

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 DTC DETERMINATION  . For diagnosing hard DTCs, proceed to appropriate DTC test. See DIAGNOSTIC TROUBLE CODE INDEX  table under ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. For diagnosing intermittent DTCs, see appropriate TROUBLE SHOOTING - NO CODES article in ENGINE PERFORMANCE.
3. If no DTCs are present and vehicle is in limp-in mode, check fused power supply circuit to transmission solenoids. A non-transmission related component system failure may cause this circuit fuse to fail. Fuses such as ERLS or SHIFT SOL fuse supply power to non-transmission related components (A/C clutch, EGR, EVAP or ABS system) which may have caused fuse to fail.
4. If no DTCs are present and a driveability problem exists, see TROUBLE SHOOTING - NO CODES article in ENGINE PERFORMANCE. Doing so will help identify proper system or component to check in appropriate SYSTEM & COMPONENT TESTING article in ENGINE PERFORMANCE.
5. After necessary repairs, clear DTCs. Verify vehicle will enter "closed loop" operation and ensure DTC does not return.