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 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. If for any reason the front axle in not able to engage when in any 4WD mode, the mode indicator in the switch will continue to flash.

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. Refer to Symptoms - Front Drive Axle. Diagnosis By Symptom - Front Drive Axle
^ Check the inline connectors C100 and C105 for proper connection, bent pins, damage, or corrosion. Refer to Harness Routing Views.
^ Check the transfer case shift control module connectors C1 and C2 for proper connection and bent or corroded pins or terminals. Refer to Repairing Connector Terminals. Diagnosis By Symptom - Front Drive Axle
^ Check for water leaks at doors and bulkhead areas. Refer to Waterleak Test Preparation.

Test Description
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 power and ground at the front axle actuator.
4. This step tests the operation of the front axle control circuit.
5. This step helps determine if the transfer case shift control module is able to monitor the front axle switch.
6. This step tests the front axle switch circuit for an open or high resistance.
7. This step measures the voltage between the front axle feed circuit and ground.
8. This step tests the front axle control circuit for an open or high resistance.
9. This step inspects the front axle for a mechanical malfunction.
10. This step tests for open fuse in the front axle feed circuit.

Step 1 - Step 12:

Step 13 - Step 15: