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 Indicator Inoperative - One or More

Circuit Description

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

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

Each time the ignition is cycled, all 5 mode indicators light simultaneously, as an indicator check to ensure proper operation of the indicators. When the ignition is ON, the transfer case shift control module illuminates the indicator lamp that corresponds to the current 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 has been 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 circuit reduces the voltage that is 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 module failures.

    3.

  3. This step tests the affected lamp circuit for an open or high resistance.

    4.

  4. This step tests the lamp feed circuit for an open or short to ground.

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 that 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 indicators ON.

Do all indicators illuminate?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3
  1. Access the back of the mode switch.
  2. Backprobe the indicator control circuit of the affected indicator to ground.

Does the affected indicator illuminate?

Go to Step 7

Go to Step 4

4

Test the affected indicator control circuit for an open or high resistance.

Did you find and correct the condition?

Go to Step 8

Go to Step 5

5

Test the LED dimming supply circuit for an open or short to ground.

Did you find and correct the condition?

Go to Step 8

Go to Step 6

6

Replace the transfer case shift control 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 within the conditions for the symptom to occur.

Does the symptom occur?

Go to Step 2

System OK