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 DTC's 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-OBD II 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.