Trouble Code Determination (Hard Or Intermittent)

During any diagnostic procedure, you must decide between "hard" failure codes and "intermittent" failure codes. Diagnostic charts will not usually help analyze "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.
2. Apply parking brake and place transmission in Neutral (man. trans.) or "P" (auto. trans.). Block drive wheels. Start engine. "SERVICE ENGINE SOON" light should go out. Run warm engine at specified curb idle for 2 minutes. Note "SERVICE ENGINE SOON" light.
3. If "SERVICE ENGINE SOON" light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal "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 "SERVICE ENGINE SOON" light does not come on, all stored trouble codes were "intermittent failures". Exceptions are noted under DIAGNOSTIC PROCEDURE.