GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 Envoy - 4WD 🢒 DTC 🢒 DTC C0550

Circuit Description

At each power-up, the transfer case shift control module runs a self-test on the following:

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

Conditions for Running the DTC
    • The ignition is ON.
    • System voltage is 9-18 volts.

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    • Masked ROM code has failed Checksum test indicating that masked ROM data is no longer valid.
    • ROM code has failed Checksum test indicating that ROM data is no longer valid.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 ROM locations have failed operational test indicating that some portions of RAM are not functional.

Action Taken When the DTC Sets
    • The SERVICE AWD indicator remains illuminated for the remainder of the current ignition cycle.
    • The transfer case control switch does not display the current position LED while DTC C0550 is current.

Conditions for Clearing the DTC
    • Replace the transfer case shift control module.
    • Perform the Diagnostic System Check - Transfer Case.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step has the technician attempt to reprogram the transfer case shift control module.

    2.

  2. This step has the technician replace and reprogram the transfer case shift control module.

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Transfer Case?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

Attempt to reprogram the transfer case shift control module. Refer to Transfer Case Shift Control Module Reprogramming .

Does the DTC set after programming?

Go to Step 3

System OK

3

Important: After transfer case shift control module replacement and reprogramming ensure all doors are closed and the key is out of the ignition, then open and close the doors again and wait 2 minutes to avoid setting false DTCs.

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement and Transfer Case Shift Control Module Reprogramming .

Did you complete the repair?

System OK

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