Principles of Operation: Notes

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

The vehicle is equipped with an intelligent 4-wheel drive (4WD) system that is always active and requires no driver input. The system has no mode select switch. The system combines transparent all-surface operation with highly capable 4WD, and is capable of handling all road conditions, including street and highway driving as well as off-road and winter driving.

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

NOTE: The active torque coupling is not repairable. If replacement is required, the active torque coupling and rear axle are replaced as an assembly. Refer to REAR DRIVE AXLE/DIFFERENTIAL .

The PTU is a gearbox that attaches to the transaxle.

On automatic transaxle vehicles, the RH halfshaft passes through the transfer case and engages the differential side gear as in normal FWD applications. The transaxle differential drives the PTU.

On manual transmission vehicles, the PTU is directly driven by a gear in the transmission. The halfshaft/intermediate shaft connects directly to the transmission differential by passing through the PTU. The PTU then drives the driveshaft at all times. The driveshaft drives one half of the rear axle clutch pack. The other half of the rear axle clutch pack drives the rear axle ring and pinion.

NOTE: PTU repair is limited to seals, gaskets and output flanges. If any of the geared components, bearings, case cover or internal shafts fail, a new transfer case must be installed.

The PTU is sealed from the transaxle and has its own oil sump. The PTU on an automatic transaxle vehicle uses 355 ml (12 oz.) of SAE 75W-140 gear lubricant. The PTU on a manual transaxle vehicle uses 350 ml (12 oz.) of SAE 80W-90 gear lubricant.

The active, on-demand 4WD system uses data from other systems as inputs to the 4WD control module. The 4WD control module uses the inputs to determine the appropriate amount of current to send to the active torque coupling that delivers the desired torque to the rear wheels. Specific inputs to the 4WD control module are:

throttle position.
transaxle range from the powertrain control module (PCM).
brake system status from the anti-lock brake system (ABS).
wheel speed from all 4 wheels from the ABS. Some outputs of the 4WD control module are:
solid-state clutch (pulse-width modulated signal) to the active torque coupling.
4WD indicator received by the instrument cluster.
percent of torque transfer commanded signal to the PCM.
torque request available signal to the ABS.