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Front Axle Will Not Engage

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					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 (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 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 in Front Drive Axle.
  • Check the inline connectors C100 and C105 for proper connection, bent pins, damage, or corrosion. Refer to Harness
      Routing Views in Wiring Systems.
  • 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 in Wiring Systems.
  • 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                                     Action                                    Values    Yes                No
Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views
       Did you perform the Diagnostic System Check - Transfer Case?                         Go to     Go to Diagnostic System
 1                                                                                   --
                                                                                            Step 2     Check - Transfer Case
           1. Install a scan tool.
           2. Turn the ignition ON, with the engine OFF.
           3. With a scan tool, command the front axle Unlocked and
 2                                                                                   --
              Locked.
                                                                                            Go to
       Does the front axle turn ON and OFF with each command?                               Step 9         Go to Step 3
           1.   Turn the ignition OFF.
           2.   Disconnect the front axle actuator.
           3.   Turn the ignition ON, with the engine OFF.
                                                                                    11-
 3         4.   Measure the voltage between the ignition 3 voltage circuit and
                                                                                   13 V
                the front axle ground circuit at the front axle actuator.
                                                                                            Go to
       Is the voltage reading within the specified value?                                   Step 4         Go to Step 7
           1. Shift the transfer case to 2WD.
           2. Connect a DMM between the ignition 3 voltage circuit and the
              front axle actuator control circuit at the front axle actuator.
 4         3. Observe the DMM while using the scan tool in order to engage           --
              the front axle.
                                                                                            Go to
       Does the DMM indicate battery voltage?                                               Step 5         Go to Step 8
           1. Connect a fused jumper wire between the ignition 3 voltage
              circuit and the axle switch signal circuit.
           2. Shift the transfer case into 4 high or 4 low.
 5                                                                                   --
       Is the mode indicator within the transfer case shift control switch on                Go to
       steady?                                                                              Step 13        Go to Step 6
       Test the front axle switch signal circuit for an open or high resistance.
       Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.
 6                                                                                   --
                                                                                             Go to
       Did you find and correct the condition?                                              Step 15        Go to Step 14
       Measure the voltage between the ignition 3 voltage circuit and ground.
                                                                                    11-
 7                                                                                           Go to
                                                                                   13 V
       Is the voltage reading within the specified range?                                   Step 12        Go to Step 10
       Test the front axle control circuit for an open or high resistance. Refer
       to Testing for Continuity and Wiring Repairs in Wiring Systems.
 8                                                                                   --
                                                                                             Go to
       Did you find and correct the condition?                                              Step 15        Go to Step 14
       Inspect the front axle for a mechanical malfunction.
 9                                                                                   --      Go to
       Did you find and correct the condition?                                              Step 15        Go to Step 13
 10 Test for an open fuse in the front axle feed circuit. Refer to Circuit           --     Go to          Go to Step 11
     Protection - Fuses and Wiring Repairs in Wiring Systems.                      Step 15

     Did you find and correct the condition?
     Repair an open in the ignition 3 voltage circuit. Refer to Testing for
     Continuity and Wiring Repairs in Wiring Systems.
11                                                                            --                --
                                                                                    Go to
     Did you complete the repair?                                                  Step 15
     Repair an open in the front axle ground circuit. Refer to Testing for
     Continuity and Wiring Repairs in Wiring Systems.
12                                                                            --                --
                                                                                    Go to
     Did you complete the repair?                                                  Step 15
     Replace the front axle switch/actuator. Refer to Electric Motor
     Actuator Replacement in Front Drive Axle.
13                                                                            --                --
                                                                                    Go to
     Did you complete the repair?                                                  Step 15
     Replace the transfer case shift control module. Refer to Transfer Case
     Shift Control Module Replacement .
14                                                                            --                --
                                                                                    Go to
     Did you complete the repair?                                                  Step 15
        1. Use the scan tool in order to clear the DTCs.
        2. Operate the vehicle to determine if the symptom has been
15         corrected.                                                         --
                                                                                   Go to
     Is the symptom still present?                                                 Step 2    System OK

				
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posted:7/21/2012
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