Front Axle Will Not Engage

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 (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

Whenever 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.

Test Description

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

2. Tests the electrical function of the front axle actuator. Helps determine between mechanical and electrical malfunctions.
3. Tests for proper power and ground at the front axle actuator.
4. Tests the operation of the front axle control circuit.
5. Helps determine if the transfer case shift control module is able to monitor the front axle switch.
6. Tests the front axle switch circuit for an open or high resistance.
7. Measures the voltage between the front axle feed circuit and ground.
8. Tests the front axle control circuit for an open or high resistance.
9. Inspects the front axle for a mechanical malfunction.
10. Tests for open fuse in the front axle feed circuit.