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 Does 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 the following components within the actuator assembly:

    • A permanent magnetic motor
    • A worm gear controlled plunger
    • A front axle switch
    • An electronic control circuit

The front axle actuator consists of the following circuits:

    • An ignition 3 voltage circuit
    • A ground circuit
    • An axle actuator control circuit
    • An axle switch signal circuit

Whenever a shift to 4WD is selected, the transfer case switch engages the front axle by grounding the axle actuator control circuit.

Test Description

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

  1. Tests for proper ignition 3 voltage to the front axle actuator.

    2.

  2. Tests for proper ground at the front axle actuator.

    3.

  3. Tests for proper ground at the axle actuator control circuit through the transfer case switch.

    4.

  4. Tests the transfer case switch ground circuit for an open.

    5.

  5. Tests the transfer case switch for proper operation.

Step

Action

Values

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

  1. Turn OFF the ignition.
  2. Disconnect the front axle actuator.
  3. Ensure the 4-wheel drive (4WD) control lever is in the 4WD position.
  4. Turn ON the ignition with the engine OFF.
  5. With a DMM, test the ignition 3 voltage circuit for proper voltage.

Does the voltage measure within the specified value?

9-14 V

Go to Step 3

Go to Step 7

3

  1. Disconnect the front axle actuator.
  2. Turn ON the ignition, with the engine OFF.
  3. With a DMM, 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 value?

9-14 V

Go to Step 4

Go to Step 8

4

  1. Turn ON the ignition, with the engine OFF.
  2. Shift the transfer case into 4HI.
  3. Connect a test lamp between the ignition 3 voltage circuit and the axle actuator control circuit, at the front axle actuator.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 5

5

  1. Disconnect the transfer case switch.
  2. Connect a test lamp from the ignition 3 voltage circuit to the transfer case switch ground circuit

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 9

6

With the control lever in the 4WD position, test for continuity across the transfer case switch.

Is continuity present across the switch?

--

Go to Step 10

Go to Step 12

7

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

Did you complete the repair?

--

Go to Step 13

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8

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

Did you complete the repair?

--

Go to Step 13

--

9

Repair the open in the transfer case switch ground circuit. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

--

Go to Step 13

--

10

Repair the open in the axle actuator control circuit. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

--

Go to Step 13

--

11

Replace the front axle actuator. Refer to Electric Motor Actuator Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the transfer case switch. Refer to Transfer Case Gear Indicator Switch Replacement .

Did you complete the repair?

--

Go to Step 13

--

13

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

Is the symptom still present?

--

Go to Step 2

System OK