Diagnostic Starting Point - Engine Controls

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. Powertrain diagnostic system check must be performed before using specific Diagnostic Trouble Code (DTC) testing procedure. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS .
2. If no DTCs are present and a driveability problem exists, diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - 4.0L AURORA article. After repairs are made, clear DTCs, verify vehicle will enter "closed loop" operation and ensure DTC does not reset.