GM Service Manual Online
For 1990-2009 cars only

This information refers to Domestic and Export calibration packages. Use the DTCs that only apply to your specific Regular Production Option ( RPO). Each DTC is directly related to a diagnostic test. The DTC sets based upon the DTCs individual running and setting criteria.

The following are the types of DTCs and their code characteristics:

Type A

    • Emissions related
    • Requests illumination of the MIL on the first trip with a fail.
    • Stores a History DTC on the first trip with a fail.
    • Stores a Freeze Frame on the first trip with a fail.
    • Stores a Failure Record.
    • Updates the Failure Record the first time the test fails each ignition cycle.

Type B

    • Emissions related
    • The code is enabled after the first trip with a fail.
    • The code is disabled if the second consecutive trip passes.
    • Requests illumination of the MIL on the second consecutive trip with a fail.
    • Stores a History DTC on the second consecutive trip with a fail.
    • Stores a Freeze Frame on the second consecutive trip with a fail.
    • Stores a Failure Record when the first test fails.
    • Updates the Failure Record the first time the test fails each ignition cycle.

Type C1

    • Non-emissions related
    • Requests illumination of the Service Lamp (not the MIL), or the service message on the first trip with a fail.
    • Stores a History DTC on the first trip with a fail.
    • Does not store a Freeze Frame.
    • Stores a Failure Record when the test fails.
    • Updates the Failure Record the first time the test fails each ignition cycle.

Type C0

    • Non-missions related
    • Does not request illumination of any lamps.
    • Stores a History DTC on the first trip with a fail.
    • Does not store a Freeze Frame.
    • Stores a Failure Record when the test fails.
    • Updates the Failure Record the first time the test fails each ignition cycle.

Type X

    • Diagnostics that are coded in the software, but will not run for non-OBD2 export vehicles.
    • Some domestic vehicles use DTCs.
    • Even though codes are not stored, the DTC Type Table can still be used as a resource when diagnosing problems with systems that are associated with the type X DTCs.

If a system is malfunctioning and the associated DTC has been disabled (Type X), it may be beneficial to use the diagnostic table as a guide to aid in diagnosis. Many of the DTC tables include a functional check of the system that may pinpoint a problem. However, it is important to remember that the DTC tables are specifically designed for use only when a DTC is set. Therefore, a thorough understanding of the normal operation of the system being diagnosed is necessary and use of the tables for this purpose is at the discretion of the technician.