Front Axle Switch Circuit Diagnosis

Circuit Description
When the four wheel drive selector is placed into a four wheel drive position, the transfer case switch closes and applies a ground to the front axle actuator/switch. The front axle actuator/switch is then engaged and a voltage is supplied to the PCM (front axle switch input) to indicate the vehicle is four wheel drive. The PCM then modifies transmission shift patterns based on this input. The PCM also sends a class 2 message to the IPC to illuminate the 4WD indicator.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

^ The following may cause an intermittent:
- Mis-routed harness
- Rubbed through wire insulation
- Broken wire inside the insulation
^ For an intermittent, refer to Symptoms. Symptom Related Diagnostic Procedures