GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 226-NP8 🢒 Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

Circuit Description

The transfer case brake control is supplied voltage at all times, with the key ON, through the B+ circuit. The brake control is activated when the transfer case shift control module registers the following modes:

    • AUTO FWD
    • 4HI
    • 4LO

This is accomplished when the transfer case shift control module provides ground to the brake control through the T-Case Lock circuit. If there is a fault in the brake control circuit, the transfer case shift control module goes into a shift block mode. The shift block mode causes the mode indicator to flash for 10 seconds when another mode is selected. After the 10 second period has ended, the indicator reverts back to the previous mode selection.

Test Description

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

  1. This step determines if the battery positive or ground circuit have an open or high resistance.

    2.

  2. This step helps to determine if the fault is due to a faulty transfer case shift module, encoder/motor assembly, or the brake control circuit.

    3.

  3. This step replaces a faulty transfer case shift control module.

    4.

  4. This step tests the T-Case Lock circuit for an open, short to ground or short to voltage.

    5.

  5. This step replaces a faulty encoder/motor assembly.

Step

Action

Yes

No

1

Important: If the transfer case shift control switch is left between the 4HI and 4LO mode detents, the transfer case defaults to AWD mode. This is considered a characteristic of the system. Ensure the switch is within the proper detents.

Did you perform the Diagnostic System Check - Transfer Case?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

Test the battery positive voltage circuit and the ground circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 7

Go to Step 3

3
  1. Turn the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. Go to ATC data list on the scan tool.
  4. Using the transfer case shift control switch, select the different modes.

Does the scan tool indicate the modes are changing?

Go to Step 5

Go to Step 4

4

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 incomplete programming or false communication 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?

Go to Step 7

--

5

Test the T-Case Lock circuit for a short to ground, short to voltage, open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

Replace the encoder motor. Refer to Transfer Case Motor/Encoder Replacement .

Did you complete the repair?

Go to Step 7

--

7
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle in order to determine if the symptom has been corrected.

Is the symptom still present?

Go to Step 2

System OK