Four Wheel Drive (4WD) Systems

WARNING: This page is about a different car, the 2008 Mercury Mariner and 2008 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

The four wheel drive (4WD) system continuously monitors vehicle conditions and automatically adjusts the torque distribution between the front and rear wheels. During normal operation, most of the torque is sent to the front wheels. If wheel slip between the front and rear wheels is detected, or if the vehicle is under heavy acceleration (high throttle position), the 4WD system increases torque to the rear wheels to prevent or control wheel slip.

The 4X4 control module varies the torque sent to the rear wheels by varying a pulse-width modulated (PWM) current to the clutch in the rear axle. The 4X4 control module also provides the brake system with its current clutch duty cycle and detemines whether or not the brake system may take command of the clutch duty cycle.

The 4WD system consists of the following:

Power take off unit (PTU)
Rear driveshaft
Coupling device control module (4X4 control module)
Rear axle with coupling device