GM Service Manual Online
For 1990-2009 cars only

Circuit Description

At each power up the module runs a self test on the following:

    • EEPROM Checksum
    • ROM Checksum
    • RAM Checksum
    • RAM Malfunction
    • Relay Malfunction

Conditions for Setting the DTC

    • Critical operational parameters stored in EEPROM have failed checksum test indicating invalid data.
    • Masked ROM code has failed checksum test indicating that masked ROM data is no longer valid.
    •  ROM code has failed checksum test indicating that ROM data is no longer valid.
    •  One or more RAM locations have failed operational test indicating that some portions of RAM are not functional.
    • Motor circuit test has indicated that the module's relay is not able to make contact.

Action Taken When the DTC Sets

The SERVICE AWD/4WD lamp will be latched on and the system will be disabled.

Conditions for Clearing the MIL/DTC

    • Replace the transfer case shift control module.
        Refer to Transfer Case Shift Control Module Replacement .
    • Perform the Transfer Case Diagnostic System Check.
        Refer to Transfer Case Diagnostic System Check .