GM Service Manual Online
For 1990-2009 cars only

Diagnostic Information

The Diagnostic Trouble Code (DTC) tables in this section are used in order to locate a faulty circuit or component through the process of elimination. The IPC performs a continual self-diagnosis on certain control functions. A DTC will set when a malfunction is detected by the IPC. The IPC will NOT turn the SERVICE ENGINE SOON Malfunction Indicator Lamp (MIL) lamp ON. The IPC will turn ON various Telltales that are related to the malfunction detected. Refer to IPC DTC list.

Class 2 Serial Data Communication

The class 2 network continually monitors various subsystems, including the following systems:

    • ATC
    • BCM
    • HVAC
    • IPC
    • PCM
    • VCM

The class 2 network continually monitors operating conditions for possible system malfunctions. By comparing system conditions against standard operating limits, certain circuit and component malfunctions may be detected. A 5-digit alphanumeric Diagnostic Trouble Code (DTC) is stored in the memory of the IPC when a malfunction is detected by this self diagnostic system. The DTC(s) may then be retrieved by the service technician using a scan tool. The scan tool may aid the technician in repairing various subsystems.

Data Link Connector (DLC)


Object Number: 384272  Size: SH

The 16-pin DLC is wired to the IPC. The 16-pin DLC is located under the dash panel on the right side. The DLC connector has terminals that are used in order to connect to a scan tool. Some common uses of the scan tool include the following functions:

    • Identifying stored Diagnostic Trouble Codes (DTCs)
    • Clearing DTCs
    • Performing output control tests
    • Reading Class 2 serial data