For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit Description

To control the front axle assembly, a front axle actuator will engage or disengage the front axle to transfer case. The front axle actuator motor consists of a permanent magnetic motor, a worm gear controlled plunger, a front axle switch and electronic control circuits all within the actuator assembly.

The front axle actuator consists of the following circuits:

• | An ignition voltage circuit

• | A ground circuit

• | The front axle control circuit

• | The front axle switch 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 the front axle is not able to engage when in 4HI or 4LO, the mode indicator in the switch button 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 .

• | A low battery condition or charging system that is faulty could contribute to the front axle to not engage. Refer to Battery Inspection/Test and Charging System Test .

### Reference Information

#### Schematic Reference

Transfer Case Control Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transfer Case Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, engine OFF, with a scan tool command the front axle to the Unlocked and Locked positions. The axle should turn ON and OFF with each command.
2. If the vehicle passes the Circuit/System Verification, then refer to Testing for Intermittent Conditions and Poor Connections .

### Circuit/System Testing

1. Ignition OFF, disconnect the front axle actuator electrical connector.
2. Verify that a test lamp illuminates between B+ and terminal E of the front axle actuator connector.

⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between terminals C and E of the front axle actuator connector.

⇒ | If the test lamp does not illuminate test the ignition 1 voltage circuit for a short to ground or an open/high resistance.

4. Ignition OFF, connect the front axle actuator electrical connector.
5. Ignition ON, connect a DMM by back probing connector C1 terminal 4 at the transfer case shift control module and ground. The DMM should measure between 10-12 volts.

⇒ | If less than the specified range, test the axle actuator control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the front axle actuator.

6. Push the 4 HI button on the accessory switch. The DMM display should switch from 10-12 volts to less than 1 volt.

⇒ | If the DMM fails to switch to less than 1 volt, replace the transfer case shift control module.

7. Ignition OFF for 30 seconds.
8. Ignition ON, connect a DMM by back probing connector C2 terminal 12 at the transfer case shift control module and ground. The DMM should measure less than 1 volt.

⇒ | If the DMM measures more than 1 volt test the axle switch signal circuit for a short to B+. If the circuit tests normal, replace the front axle actuator.

9. Push the 4 HI button on the accessory switch. The DMM display should switch from less than 1 volt to 10-12 volts.

⇒ | If the DMM voltage display fails to switch to 10-12 volts, test the axle switch signal circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the front axle actuator.

10. If all circuits test normal, replace the transfer case shift control module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for transfer case shift control module replacement, setup, and programming.

• | Electric Motor Actuator Replacement