DTC 004. GMC Truck Envoy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 Envoy - 4WD 🢒 DTC 🢒 DTC 004

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

•	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.

The condition for setting the DTC is not present and a momentary loss of battery power at the battery positive voltage circuit, CKT 40.

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

This step replaces the transfer case shift control module.

Step	Action	Yes	No
Schematic Reference: Transfer Case Control Schematics
1	Important: Check the transfer case shift control module for DTCs. The transfer case shift control module is not a class 2 device. DTCs are displayed on the transfer case shift control switch. Use the following four steps to obtain DTCs. Turn OFF the ignition for 10 seconds. Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side. Turn ON the ignition, with the engine OFF. Observe the transfer case shift control switch select buttons for flashing codes. 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 replacement?	Go to Step 3	--
3	Clear all DTCs from memory. Refer to Diagnostic Trouble Code (DTC) Clearing . Operate the vehicle while pressing each of the buttons on the transfer case shift control switch. Does the DTC reset?	Go to Step 2	System OK