Principles of Operation

WARNING: This page is about a different car, the 2017 Lincoln Navigator and 2017 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

The Navigator is equipped with an automatic, electronic-shift system that allows the operator to choose between 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