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 MIL located on instrument cluster. When a malfunction is detected and MIL is turned on, a corresponding 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. PCM records the operating conditions at the time diagnostic failed into Failure Records and Freeze Frame.
• Type "B"
  
  Emission related faults that illuminate MIL if a fault occurs in 2 consecutive ignition cycles. PCM records the operating conditions at the time diagnostic failed the first time into Failure Records and Freeze Frame. When diagnostic fails a second time, PCM records the operating conditions at the time diagnostic failed into Freeze frame and updates Failure Records.
• Type "C"
  
  Non-emission related faults that do not illuminate MIL but the DTC will be recorded in memory. PCM records the operating conditions at the time diagnostic failed into Failure Records, no Freeze Frame information will be saved. Driver information center (if equipped) may display a message.

A current DTC clears when the diagnostic runs and passes. A history DTC clears after 40 consecutive warm-up cylcles, if no failures are reported by this or any other diagnostic. Intermittent failures may be caused by sensor, connector or wiring related problems. See TROUBLE SHOOTING - NO CODES - TRUCKS article.