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Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  This step checks that the scan tool is communicating with the transfer case shift control module (TCCM).
  2. 3:  This step checks the presence of DTCs which begin with "U" indicating some other module is not communicating.
  3. 4:  This step checks to see if other modules are interfering with the TCCM operation.
  4. 6:  This step checks for TCCM DTCs.
  5. 7:  This step verifies if the TCCM has power and ground. The TCCM will not communicate without the Battery Positive Voltage circuit functioning.
Diagnostic System Check - Transfer Case

Step Action Yes No
1 Install a scan tool.
Does the scan tool power up?		 Go to Step 2  Go to Scan Tool Does Not Power Up in Data Link Communications
2 
    IMPORTANT: A new TCCM from the manufacturer comes with the latest calibrations for that vehicle. A Service/Replacement TCCM does not come with vehicle specific calibrations. If the scan tool does not communicate with the TCCM, it may be due to incomplete or missing files. Refer to Transfer Case Control Module Reprogramming .
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to establish communication with the TCCM.
Does the scan tool communicate with the TCCM?		 Go to Step 3  Go to Step 7 
3  Does the scan tool display any current DTCs which begin with a "U"? Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications Go to Step 4 
4  Does the scan tool display any VSS DTCs? Go to Diagnostic System Check - Automatic Transmission in Automatic Transmission - 4L80-E/4L85-E or Diagnostic System Check - Automatic Transmission in Automatic Transmission - Allison Go to Step 5 
5 Does the scan tool display any Electronic Brake Control Module (EBCM) DTCs? Go to Diagnostic System Check - ABS in Antilock Brake System Go to Step 6 
6  Does the scan tool display any TCCM DTCs? Go to Diagnostic Trouble Code (DTC) List  Go to Symptoms - Transfer Case 
7 
IMPORTANT: If there are multiple TCCM DTCs, diagnose the DTCs in the order listed in the DTC list.
Test the battery positive voltage, ATC Class 2 Serial Data and ground circuits of the TCCM for an open, high resistance, short to ground and short to voltage.Did you find a condition with the circuits?		 Go to Step 9  Go to Step 10 
8
  1. Flash the TCCM with the most current calibrations.
  2. Test drive the vehicle.
Did the 4WD system operate normally without setting any DTCs?		 System OK Go to Step 3 
9 Repair the open, high resistance or short in the affected circuits.
Did you complete the repair?		 Go to Step 11  -
10 Replace the TCCM. Refer to Transfer Case Shift Control Module Replacement  and Transfer Case Control Module Reprogramming .
Did you complete the replacement?		 Go to Step 11  -
11 Test drive the vehicle.
Does the vehicle 4WD system operate normally without setting any DTCs?		 System OK Go to Step 1 
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