Four-Wheel Drive Does Not Engage

Four-Wheel Drive Does Not Engage

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Circuit/System Description

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator consists of the following components within the actuator assembly:

* A permanent magnetic motor
* A worm gear controlled plunger
* A front axle switch
* An electronic control circuit

The front axle actuator consists of the following circuits:

* An ignition 3 voltage circuit
* A ground circuit
* An axle actuator control circuit
* An axle switch signal circuit

Whenever a shift to 4WD is selected, the transfer case switch engages the front axle by grounding the axle actuator control circuit.

Reference Information
Schematic Reference

Transfer Case Control Schematics (MP 1222/1225/1226-NQG - Transfer Case)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Circuit/System Verification

1. Place the vehicle in 4WD install a scan tool and using engine data 2 look at the display for 4WD signal.
2. Verify that the scan tool indicates that the vehicle is in 4WD.

• If the scan tool indicates that the vehicle is in 2WD go to circuit system testing.

Circuit/System Testing

1. Check the axle switch signal circuit for an open or high resistance.

• If everything checks normal then go to the next step.

2. Check the front axle actuator control circuit for an open or high resistance with the front axle actuator disconnected and the mode selection switch disconnected.

• If everything checks normal reconnect the mode selection switch and retest. If the circuit still shows an open or high resistance then replace the switch. If the circuit indicates no open or high resistance then refer to front axle actuator and axle testing.

Front Axle Actuator and Axle Testing

Remove the actuator and attempt shift from 2WD to 4WD, if the actuator moves check the front axle actuator plunger and fork assembly.

If the actuator does not function properly then replace the front axle actuator.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Front Drive Axle Actuator Replacement (Service and Repair)
* Transfer Case Control Lever Replacement (Service and Repair)
* Transfer Case Control Rod Replacement (Service and Repair)
* Front Drive Axle Clutch Fork Inspection (Front Drive Axle Clutch Fork Inspection)