Hard Or Intermittent Trouble Code Determination

During any diagnostic procedure, determine if codes are due to hard or intermittent failure. Diagnostic charts will not usually help diagnose intermittent codes. To determine hard codes and intermittent codes, proceed as follows:

1. MANUALLY enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes. See CLEARING TROUBLE CODES.
2. Apply parking brake and place transmission in Neutral or Park. Block drive wheels and start engine. MIL should go out. Run warm engine at specified curb idle for 2 minutes and note MIL.
3. If MIL comes on, manually enter diagnostic mode. Read and record trouble codes. This reveals hard failure codes. Codes 13, 15, 24, 44, 45 and 55 may require a road test to reset hard failure after trouble codes were cleared.
4. If MIL does not come on, all stored trouble codes were intermittent failures. Exceptions are noted under DIAGNOSTIC PROCEDURE.