Four Wheel Drive (4WD) Systems 1-Speed Torque-On-Demand: Notes

Courtesy of FORD MOTOR COMPANY	Flex Probe Kit 105-R025D or equivalent
Courtesy of FORD MOTOR COMPANY	Fluke 77-IV Digital Multimeter FLU77-4 or equivalent
Courtesy of FORD MOTOR COMPANY	Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool

Principles of Operation 

The Navigator is equipped with an automatic, electronic-shift system that allows the operator to choose between 3 different modes: 4X2, 4X4 AUTO and 4X4. The operator uses the mode select buttons to switch between any mode at any speed.

Wheel slip is sensed by monitoring the average front and rear wheel speeds. Based on steering wheel angle, accelerator pedal position and wheel slip, a PWM signal is transmitted to the transfer case as torque is required. The TCCM provides the ABS with current clutch duty cycle and whether or not ABS may command the clutch duty cycle.

The brake subsystem sends the following information signals to the 4WD system over the HS-CAN :

• Occurrences of brake events and failures. Refer to Anti-Lock Brake System (ABS) and Stability Control .
• Steering wheel angle status. Refer to Anti-Lock Brake System (ABS) and Stability Control .
• Wheel speeds. Refer to Anti-Lock Brake System (ABS) and Stability Control .

A concern with any of the above listed brake system signals or the HS-CAN affects 4WD system operation.

The APP output signal is provided to the TCCM from the PCM. This signal is used by the TCCM in controlling the transfer case clutch.

The TCCM sends a duty cycle command to the clutch coil which activates the clutch within the transfer case.

The TCCM varies the torque sent to the front driveline by controlling the transfer case clutch. At rest and under cruising conditions, the TCCM activates the transfer case clutch at minimum duty cycle (percentage of time the clutch is turned on), which allows for the slight difference between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. The TCCM increases the duty cycle to prevent or control slip under any of the following conditions:

• Slip is detected
• Heavy acceleration (throttle position)
• Straight-ahead steering wheel angle

Feature inputs:

• MSS
• APP (from the PCM)
• Steering wheel angle (from the ABS module)
• TR position (from the PCM)
• Transmission output torque (from the PCM)
• Wheel speed signal (transmitted from the ABS module)

Feature outputs:

• Solid state PWM signal
• Message center 4WD mode indicators

Inspection and Verification 

1. 1.
   
   Verify the customer concern.

1. 2.
   
   Visually inspect for obvious signs of mechanical or electrical damage.

Visual Inspection Chart 

Mechanical	Electrical
Halfshafts IWE Driveshaft and U-joints Vacuum leaks Fluid leaks Matching tire sizes Transfer case	BJB fuses: 27 (20A) 29 (10A) SJB fuse 35 (10A) TCCM MSS IWE solenoid Wiring harness Connector(s) Circuitry

1. 3.
   
   If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.

NOTE: Make sure to use the latest scan tool software release.
1. 4.
   If the cause is not visually evident, connect the scan tool to the DLC.

NOTE: The VCM LED prove-out confirms power and ground from the DLC are provided to the VCM.
1. 5.
   If the scan tool does not communicate with the VCM :
   • check the VCM connection to the vehicle.
   • check the scan tool connection to the VCM.
   • refer to Module Communications Network , No Power To The Scan Tool, to diagnose no power to the scan tool.

1. 6.
   
   If the scan tool does not communicate with the vehicle:
   • verify the ignition is in the ON position.
   • refer to Module Communications Network to diagnose no response from the PCM.

1. 7.
   
   Carry out the network test.
   • If the scan tool responds with no communication for one or more modules, refer to Module Communications Network .
   • If the network test passes, retrieve and record CMDTCs.

1. 8.
   
   Clear the DTCs and carry out the self-test diagnostics for the TCCM.

NOTE: Before carrying out the on-demand self-test, make sure that:
1. 9.
   
   • the ignition is in RUN.
   • 2WD mode is selected.

   If the DTCs s retrieved are related to the concern, go to the TCCM DTC Chart . For all other DTCs, refer to Multifunction Electronic Modules .

1. 10.
   
   If no DTCs related to the concern are retrieved, GO to SYMPTOM CHART - 4WD  or GO to SYMPTOM CHART - NVH .