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. DO NOT  proceed with testing unless all other problems have been repaired. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  before using CIRCUIT TESTS.
2. Check for any Technical Service Bulletins (TSBs) that may apply. Retrieve any DTCs that may be present. If DTCs were displayed, follow procedures in appropriate CIRCUIT TEST.
3. If DTCs were not displayed, and a driveability problem or intermittent problem exists, go to the TESTS W/O CODES article.
   NOTE: ALWAYS clear DTCs, confirm closed loop operation, and test drive vehicle after repairs are made. Ensure MIL does NOT illuminate.