Self-Diagnostic System: Notes

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 turned on, a corresponding Diagnostic Trouble Code (DTC) will be stored in PCM memory. Malfunctions are designated as either "emission related" or as "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. DTC and history will be recorded into Failure Records and Freeze Frame.
• Type "C"
  
  Non-emission related faults that do not illuminate MIL but the DTC will be recorded in memory. No Freeze Frame information will be saved.

Emission related DTCs (type "A" or "B") cause MIL to illuminate and remain on until the malfunction is repaired. On models using digital display on dash to indicate DTCs, DTCs may be accompanied by a "current" or "history" indication for intermittent and hard failures. If MIL comes on and remains on during vehicle operation, cause of malfunction must be determined using appropriate diagnostic procedure for affected DTC located in appropriate SELF-DIAGNOSTICS article. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional but loss of good driveability is likely.

Non-emission related DTCs (type "C") do not illuminate the MIL. The corresponding DTC, however, will be retained in PCM memory. On models equipped with a Digital Information Center (DIC) may display a message. If related DTC does not reoccur within 50 engine restarts, related DTC will be erased from PCM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See appropriate TROUBLE SHOOTING - NO CODES article.