GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC Sierra Denali 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 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 motor consists of a permanent magnetic motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.

The front axle actuator consists of the following circuits:

    • The front axle control circuit, which is also connected to the transfer case shift control module
    • The front axle switch circuit, which is also connected to the transfer case shift control module
    • A battery feed circuit
    • A ground circuit

When a shift to 4HI or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle 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 and helps determine 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 front axle 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 front axle switch circuit for an open or high resistance.

    6.

  6. This step measures the voltage between the front axle feed circuit and ground.

    7.

  7. This step tests the front axle 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 front axle feed circuit.

Step

Action

Values

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

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

Is the voltage reading within the specified value?

11-13 V

Go to Step 4

Go to Step 7

4

  1. Connect a test lamp between the ignition 3 voltage circuit and the front 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 front axle actuator signal circuit.
  2. Use the scan tool in order to read the Front Axle Switch parameter.

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

--

Go to Step 13

Go to Step 6

6

Test the front axle actuator signal circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs.

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.

Is the voltage reading within the specified range?

9-14 V

Go to Step 12

Go to Step 10

8

Test the front axle control circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs.

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 front axle feed circuit. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

11

Repair an open in the front axle feed circuit. Refer to Wiring Repairs.

Did you complete the repair?

--

Go to Step 15

--

12

Repair an open in the front axle ground circuit. Refer to Wiring Repairs.

Did you complete the repair?

--

Go to Step 15

--

13

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

Did you complete the repair?

--

Go to Step 15

--

14

Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the repair?

--

Go to Step 15

--

15
  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