DTC C0550. GMC Truck Safari

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2004 🢒 Safari - 4WD 🢒 DTC 🢒 DTC C0550

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

•	The ignition is ON.

•	The system voltage is 9-16 volts.

•	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•	Masked ROM code has failed Checksum test indicating that masked ROM data is no longer valid.

•	ROM code has failed Checksum test indicating that ROM data is no longer valid.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.

•	Motor circuit test has indicated that one of the module's relays is not able to make contact.

•	The SERVICE AWD indicator is illuminated for the remainder of the current ignition cycle.

•	All clutch activation, slip control is disabled.

•	Replace the transfer case shift control module.

•	Perform the Diagnostic System Check - Transfer Case .

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

This step replaces the transfer case shift control module.

Step	Action	Yes	No
Schematic Reference: Transfer Case Control Schematics
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	--

Step

Action

Yes

Did you perform the Diagnostic System Check - Transfer Case?

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

Did you complete the repair?

System OK