Front Axle Will Not Disengage

Front Axle Will Not Disengage

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 (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 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 AUTO 4WD, 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.

Diagnostic Aids
A mechanical condition inside the front axle could prevent the shift fork from moving causing the motor to be stuck in one position.

Test Description

Steps 1-14:

Steps 15-17:

The numbers below refer to the step numbers on the diagnostic table.
2. This step tests the electrical function of the front axle actuator and helps determine mechanical and electrical malfunctions.
3. This step tests for proper voltage and ground at the front axle actuator.
4. This step tests the operation of the front axle actuator control circuit.
5. This step tests the electrical function of the front axle actuator control circuit.
6. This step tests for proper supply voltage to the front axle actuator.
7. This step tests for open fuse in the ignition 3 voltage circuit.
8. This step tests the front axle actuator control circuit for an open or high resistance.
9. This step tests the front axle actuator signal circuit for an open or high resistance.
10. This step helps determine if the front axle actuator has a mechanical malfunction.
11. This step tests the front axle switch circuit for a short to voltage.
12. This step inspects the front axle for a mechanical malfunction.