Self-Diagnostic System: Description

The PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. When a malfunction is detected and MIL is illuminated, a corresponding Diagnostic Trouble Code (DTC) will be stored in PCM memory. Malfunctions are designated as either "emission related" or "non-emission related", and are divided into 4 code types to identify type of fault. The 4 code types are defined as follows:

Type "A"

Emission related faults that illuminate MIL at first occurrence of a fail condition.

Type "B"

Emission related faults that illuminate MIL if a fault occurs in 2 consecutive ignition cycles.

Type "C"

Non-emission related faults that do not illuminate MIL. Driver Information Center (DIC) may display a message.

Emission related DTCs (type "A" or "B") cause MIL to illuminate and remain on until the malfunction is repaired. If MIL illuminates and remains on during vehicle operation, cause of malfunction must be determined using affected Diagnostic Trouble Code (DTC) located in appropriate SELF-DIAGNOSTICS article. PCM records and updates failure records/operating conditions to Freeze Frame. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional but impaired driveability is likely. Use a scan tool to clear codes and turn off MIL.

Non-emission related DTCs (type "C") do not illuminate the MIL, but may display a message on the Driver Information Center (DIC). The corresponding diagnostic trouble code, however, will be retained in PCM memory. PCM records operating conditions at time of failure into memory. If related fault does not reoccur within 40 engine restarts, related diagnostic trouble code will be erased from PCM memory. Intermittent failures may be caused by a sensor, connector or wiring related problem. See appropriate TROUBLE SHOOTING - NO CODES article.