GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 226-NP8 🢒 Transfer Case Shift Control Switch Inoperative

Circuit Description

The range/mode switch circuit consists of the following 5 switches:

    • 4HI
    • AUTO 4WD
    • 2HI
    • 4LO
    • Neutral

The transfer case shift control module supplies a regulated 5 volts DC to the switch through the 5 volt regulator circuit. The current travels through the resistor of the currently active switch. The switch then returns current to the transfer case shift control module through the switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage to determine the condition of the mode switch circuit.

When each switch is depressed, the switch completes a circuit through the respective resistor. The transfer case shift control module continuously monitors the switch input to determine which of the following buttons were selected:

    • 4HI
    • AUTO 4WD
    • 2HI
    • 4LO

Test Description

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

  1. This step tests the functionality of the mode switch.

    2.

  2. This step tests the modules ability to operate the transfer case modes.

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

  1. Install a scan tool.
  2. Start the engine.
  3. Place the transmission into NEUTRAL.
  4. Set the parking brake.
  5. Observe Commanded Mode Indicator States on the scan tool, while selecting each of the mode positions.

Does the state change with the selection of any of the mode positions?

Go to Step 5

Go to Step 3

3

  1. Use a scan tool in order to command through the modes of the transfer case shift control switch.
  2. With a scan tool, command through all Commanded Mode Indicator states.

Does the Mode Indicator state change?

Go to Step 4

Go to Step 5

4

Replace the transfer case shift control switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the repair?

Go to Step 6

--

5

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 6

--

6
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the conditions for the symptom to occur.

Does the symptom occur?

Go to Step 2

System OK