GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Classic - 4WD 🢒 Transmission/Transaxle 🢒 Transfer Case - NVG 261-NP2 🢒 Four-Wheel Drive Indicator Always On

Circuit Description

The 4WD indicator lamp is located in the instrument panel cluster (IPC). Ignition 1 voltage is supplied to the IPC when the ignition switch is in the START or RUN position. When the vehicle is in START or RUN and the powertrain control module (PCM) receives the axle switch signal from the front axle actuator, the PCM sends a class 2 signal to the IPC, turning on the 4WD indicator. The 4WD indicator stays on as long as the axle switch signal input is present.

Test Description

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

  1. This step tests for an intermittent condition.

    2.

  2. This step determines whether the condition is the result of a faulty 4WD system.

    3.

  3. This step determines if the condition is the result of a faulty IPC.

    4.

  4. This step determines if the condition is the result of a faulty PCM.

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Did you perform A Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Verify the condition is present.

Does the system operate normally?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

Does the front axle disengage when the 4WD control lever is in the 2WD position?

--

Go to Step 4

Go to Four-Wheel Drive Does Not Disengage

4

  1. Turn ON the ignition, with the engine OFF.
  2. Install a scan tool.
  3. Use the scan tool through IPC output controls to command all indicators OFF on the IPC.

Does the 4WD indicator turn OFF when all indicators are turned OFF?

--

Go to Step 5

Go to Step 8

5

Test the axle switch signal circuit for voltage at the PCM.

Does the voltage measure within the specified value?

9-14 V

Go to Step 6

Go to Step 7

6

Inspect the axle switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . If OK, replace the front axle actuator. Refer to Electric Motor Actuator Replacement .

Did you complete the replacement?

--

Go to Step 9

--

7

Replace the PCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 9

--

8

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

--

Go to Step 9

--

9

Operate the vehicle in order to determine if the condition has been corrected.

Is the condition still present?

--

System OK

Go to Step 2