GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Canyon Pickup - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - Isuzu T150 🢒 Front Axle Will Not Disengage

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

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 transfer case is shifted to 2WD and the front axle is still engaged the 2WD mode indicator within the transfer case shift control switch will continue to flash indicating a failure.

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 in Front Drive Axle.

Test Description

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

  1. This step tests the electrical function of the front axle actuator and helps determine mechanical and electrical malfunctions.

    2.

  2. This step tests for proper voltage and ground at the front axle actuator.

    3.

  3. This step tests the operation of the front axle actuator control circuit.

    4.

  4. This step tests the electrical function of the front axle actuator control circuit.

    5.

  5. This step tests for proper supply voltage to the front axle actuator.

    6.

  6. This step tests for open fuse in the ignition 3 voltage circuit.

    7.

  7. This step tests the front axle actuator control circuit for an open or high resistance.

    8.

  8. This step tests the front axle actuator signal circuit for an open or high resistance.

    9.

  9. This step helps determine if the front axle actuator has a mechanical malfunction.

    10.

  10. This step tests the front axle switch circuit for a short to voltage.

    11.

  11. This step inspects the front axle for a mechanical malfunction.

Step

Action

Values

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Transfer Case?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2
  1. Turn the ignition ON, with the engine OFF.
  2. Ensure that the vehicle is in 2WD mode
  3. Observe the 2WD mode indicator within the transfer case shift control switch.

Is the 2WD indicator flashing?

--

Go to Step 10

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the front axle actuator.
  3. Turn the ignition ON, with the engine OFF.
  4. Measure the voltage between the ignition 3 voltage circuit and the front axle ground circuit at the front axle actuator.

Is the voltage reading within the specified values?

11-13 V

Go to Step 4

Go to Step 6

4
  1. Connect a DMM between the ignition 3 voltage circuit and the front axle control circuit at the front axle actuator.
  2. Observe the DMM, while using the scan tool in order to engage the front axle.

Does the DMM indicate battery voltage?

--

Go to Step 5

Go to Step 8

5
  1. Connect a fused jumper wire between the ignition 3 circuit and the front axle switch circuit.
  2. Observe the 2WD indicator inside the transfer case shift control switch.

Does the 2WD indicator flash?

--

Go to Step 16

Go to Step 9

6

Measure the voltage between the ignition 3 voltage circuit and ground.

Is the voltage reading within the specified values?

11-13 V

Go to Step 14

Go to Step 7

7

Test for an open fuse in the front ignition 3 voltage circuit. Refer to Circuit Protection - Fuses and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

8

Test the front axle control circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

9

Test the actuator switch signal circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

10
  1. Disconnect the front axle actuator.
  2. Observe the 2WD mode indicator within the transfer case shift control switch.

Is the 2WD indicator flashing?

--

Go to Step 11

Go to Step 13

11

Test the front axle actuator signal circuit for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 12

12
  1. Disconnect connector C1 and C2 at the module.
  2. With the front axle actuator disconnected check the front axle control circuit for a short to ground. Refer to Testing for Short to Ground in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

13

Inspect the front axle for a mechanical malfunction.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

14

Repair an open in the front axle actuator ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 18

--

15

Repair an open in the ignition 3 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 18

--

16

Replace the front axle switch/actuator. Refer to Electric Motor Actuator Replacement in Front Drive Axle.

Did you complete the repair?

--

Go to Step 18

--

17

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement .

Did you complete the repair?

--

Go to Step 18

--

18
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle to determine if the symptom has been corrected.

Is the symptom still present?

--

Go to Step 2

System OK