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 Always On - Two or More

Circuit Description

The indicator lamps circuit consist of the following 5 individual lamps contained inside the mode/range switch assembly:

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

The following lamps are contained inside their respective range button:

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

When the ignition in ON, the transfer case shift control module illuminates the indicator that corresponds to the current automatic temperature control (ATC) gear position, by providing a ground through a current limiting driver.

The transfer case shift control module flashes each indicator lamp after a shift is requested and continues to flash until the transfer case shift control module completes the shift.

A solid state circuit, located inside the switch, supplies ignition voltage to the lamps. The solid state circuit also receives voltage when the headlamp switch is in the parklamp or headlamp position. When the solid state circuit receives voltage from the headlamp switch, the switch reduces the voltage supplied to the indicator lamps, dimming the lamps when the headlamps are ON.

Test Description

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

  1. This step tests the transfer case electrical control of the lamp circuits.

    2.

  2. This step helps determine a short to ground in the suspect lamp circuits.

    3.

  3. This step tests the suspect lamp circuits for a short to ground.

    4.

  4. This step repairs a short to ground in the suspect lamp circuit.

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 the 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. Turn the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. Using a scan tool, command all the indicator lamps OFF.

Do all the lamps go OFF?

Go to Step 7

Go to Step 3

3

  1. Using a scan tool, determine the transfer case mode.
  2. Use this information to determine which lamp circuits are at fault.
  3. Disconnect the transfer case shift control switch.
  4. Test the suspect lamp circuits for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the suspect circuits shorted to ground?

Go to Step 4

Go to Step 6

4

  1. Disconnect the transfer case shift control module.
  2. Test the suspect lamp circuits for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Is the suspect circuits shorted to ground?

Go to Step 5

Go to Step 7

5

Repair short to ground in the suspect lamp circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

--

6

Replace the mode switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the repair?

Go to Step 8

--

7

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 8

--

8
  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