Failure Code Determination

During any diagnostic procedure, "hard failure" codes MUST be distinguished from "intermittent failure" codes. Diagnostic charts CANNOT be used to analyze "intermittent failure" codes, except as noted under Diagnostic Procedure. To determine "hard failure" codes and "intermittent failure" codes, proceed as follows:

1. Turn ignition on and enter diagnostics. Read and record all stored trouble codes. Exit diagnostics and clear trouble codes.
2. Apply parking brake and place transmission in neutral (manual) or park (automatic). Block drive wheels. Start engine. "CHECK ENGINE" lamp should go out. Run warm engine at specified curb idle for 2 minutes and note "CHECK ENGINE" light.
   NOTE: Grounding "TEST" terminal with engine running will force engine to operate in closed loop mode if engine is warm and oxygen sensor is hot. If "CHECK ENGINE" lamp does not glow while in closed loop, CCC system is operating properly.
3. If "CHECK ENGINE" lamp comes on, enter diagnostics, read and record trouble codes. This will reveal "hard failure" codes. Codes "13", "15", "24", "44", "45" and "55" may require road test to reset "hard failure" after trouble codes were cleared.
4. If "CHECK ENGINE" lamp does not come on, all stored trouble codes were "intermittent failures", except as noted under Diagnostic Procedure.
   NOTE: Trouble code "15" malfunction will only display after 5 minutes of engine operation. Trouble code "12" will display only during time of no reference pulses received by ECM; it will never be stored as a malfunction.