GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 263-NP1 (Selectable) 🢒 Front Axle Will Not Engage

Circuit Description

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator consists of a Permanent Magnetic (PM) motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.

The front axle actuator has four circuits connected:

    • Ignition 3 voltage circuit
    • Ground circuit
    • Axle actuator control circuit
    • Axle switch signal circuit

Whenever a shift to 4HI, or 4LO is requested, the transfer case shift control module engages the front axle by grounding the axle actuator control circuit through a current limiting driver.

Test Description

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

  1. This step tests the electrical function of the front axle actuator. This step helps determine between mechanical and electrical malfunctions.

    2.

  2. This step tests for proper power and ground at the front axle actuator.

    3.

  3. This step tests the operation of the axle actuator control circuit.

    4.

  4. This step helps determine if the transfer case shift control module is able to monitor the front axle switch.

    5.

  5. This step tests the axle switch signal circuit for an open or high resistance.

    6.

  6. This step measures the voltage between the ignition 3 voltage circuit and ground.

    7.

  7. This step tests the axle actuator control circuit for an open or high resistance.

    8.

  8. This step inspects the front axle for a mechanical malfunction.

    9.

  9. This step tests for open fuse in the ignition 3 voltage circuit.

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Was the Transfer Case Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the front axle Unlocked and Locked.

Does the front axle turn ON and OFF with each command?

--

Go to Step 9

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the front axle actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage between the ignition 3 voltage circuit and the ground circuit at the front axle actuator.

Does the voltage measure within the specified values?

9-14 V

Go to Step 4

Go to Step 7

4

  1. Connect a test lamp between the ignition 3 voltage circuit and the axle actuator control circuit at the front axle actuator.
  2. Observe the test lamp, while using the scan tool in order to engage the front axle.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 8

5

  1. Connect a fused jumper wire between the ignition 3 voltage circuit and the axle switch signal circuit.
  2. Use the scan tool in order to read the Front Axle Switch status.

Does the scan tool display the Front Axle Switch status Locked?

--

Go to Step 13

Go to Step 6

6

Test the axle switch signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

7

Measure the voltage between the ignition 3 voltage circuit and ground.

Does the voltage measure within the specified values?

9-14 V

Go to Step 12

Go to Step 10

8

Test the axle actuator control circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

9

Inspect the front axle for a mechanical malfunction.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

10

Test for open fuse in the ignition 3 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

11

Repair an open in the ignition 3 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 15

--

12

Repair an open in the ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 15

--

13

Replace the front axle actuator. Refer to the Electric Motor Actuator Replacement in Front Drive Axle.

Did you complete the repair?

--

Go to Step 15

--

14

Replace the transfer case shift control module. Refer to the Transfer Case Shift Control Module Replacement .

Did you complete the replacement?

--

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the conditions for allowing the symptom to re-occur.

Does the symptom re-occur?

--

Go to Step 2

System OK