Self-Diagnostic System: Notes

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The ECM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, ECM 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 ECM 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. ECM 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. ECM records the operating conditions at the time diagnostic failed the first time into Failure Records and Freeze Frame. When diagnostic fails a second time, ECM 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. ECM 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 cycles, 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 - 6.6L SIERRA & SILVERADO - DIESEL article.