On-Board Diagnostics: Notes

WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will store a Diagnostic Trouble Code (DTC) and, in most cases, illuminate the Malfunction Indicator Light (MIL) located on instrument cluster.

The PCM also monitors the Fuel Injector Control Module (FICM) diagnostic input circuit in order to set FICM related DTCs. The FICM is a non-flashable control module that is not capable of serial data communication. The FICM diagnostic circuit is a 5-volt circuit that is Pulse Width Modulated (PWM) by the FICM in order to communicate diagnostic information to the PCM.

There are 2 paths for accessing on-board diagnostics. It is necessary to access information through both paths, as each path presents some different information.

Generic OBD-II

This provides all generic codes and some OEM codes, serial data PIDs required for generic OBD-II and some OEM PIDs, monitor status, pending codes and freeze frame.

OEM

All DTCs, all PIDs, failure records, enhanced scan tool information and all other OEM scanner functions.