Self-Diagnostic Systems: Description: Notes

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

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 3 code types to identify type of fault. The 3 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, the cause of the malfunction must be determined using affected DTC. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO 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. The PCM turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

Non-emission related DTCs (type "C") do not illuminate the MIL, but may display a message on the Driver Information Center (DIC), if equipped. The corresponding DTC, 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 warm-up cycles, related DTC will be erased from PCM memory. Intermittent failures may be caused by a sensor, connector or wiring related problem. See TROUBLE SHOOTING - NO CODES - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.