Self-Diagnostic System: Notes

The PCM/VCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM/VCM 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/VCM 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.
• Type "C"
  
  Non-emission related faults that illuminate MIL only when fault is present. MIL will turn off 3 seconds after engine start if fault is no longer present, but a record of fault will remain stored in memory.
• Type "D"
  
  Non-emission related faults which do not illuminate MIL. 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 TESTS W/CODES 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") cause MIL to flicker or glow and go out about 10 seconds after the intermittent fault goes away. The corresponding DTC, however, will be retained in PCM/VCM memory. 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 related DTC does not reoccur within 50 engine restarts, related DTC will be erased from PCM/VCM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See TROUBLE SHOOTING - BASIC PROCEDURES article.