GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Blazer - 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
    • Relay Malfunction

Conditions for Running the DTC
    • The ignition is ON.
    • System voltage is 9-16 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 not valid.
    • ROM code has failed Checksum test indicating that ROM data is not valid.
    • One or more ROM locations have failed operational test indicating that some portions of RAM are not functional.
    • Motor circuit test has indicated that one of the modules relays is not able to make contact.

Action Taken When the DTC Sets
    • The SERVICE 4WD indicator remains illuminated and the system is disabled.
    • No further mode changes for the current ignition cycle.

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

Test Description

The number below refers to the step number on the diagnostic table

  1. This step replaces 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

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

Did you complete the repair?

System OK

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