Principles of Operation

WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 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 4X4 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 4X4 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. For additional information, refer to REAR DRIVE AXLE/DIFFERENTIAL article.

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 4X4 control module. The 4X4 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 4X4 control module are:

throttle position.
transaxle range from the PCM.
brake system status from the ABS.
wheel speed from all 4 wheels from the ABS.

Some outputs of the 4X4 control module are:

solid-state clutch (pulse-width modulated signal) to the active torque coupling.
4WD indicator received by the instrument cluster (IC).
percent of torque transfer commanded signal to the PCM.
torque request available signal to the ABS.

Heat Protection Mode - During very extreme off-road operation, the 4WD system has a heat protection system to protect the active torque coupling from damage. If the system detects an overheat condition, it enters a locked mode and turns on the 4WD indicator light in the IC. If the heat in the system continues to rise once in the locked mode, the 4X4 control module disables the active torque coupling and causes the 4WD indicator light to flash continuously.

4WD Indicator Light - 4WD - Illuminates continuously when the 4WD system is locked in 4WD due to its heat protection mode. In the locked mode, the vehicle resists turning and binds up when driven on dry pavement. To exit the locked mode, stop the vehicle and allow it to cool for 5 minutes with the engine running. When the 4WD indicator turns OFF, normal 4WD system function is restored.

4WD - Blinks continuously when the 4WD system is disabled due to its heat protection mode. To exit the disabled mode, stop the vehicle and allow it to cool for 5 minutes with the engine running. When the indicator turns OFF, normal 4WD system function is restored.

4WD - Blinks 3, 6, 8 or 10 times every minute when the 4WD system requires service. Use a scan tool to check for DTCs. Refer to the 4X4 Control Module DTC Chart.

Blinks	Cause
3	Cluster is not receiving the 4WD indicator message from the 4X4 control module
6	Invalid throttle position data received from the PCM
8	Invalid wheel speed data received from the ABS module
10	Active torque coupling circuit fault

4WD Messages in Message Center - SERVICE 4WD - Displayed when the 4WD system requires service. Use a scan tool to check for DTCs. Refer to the 4X4 Control Module DTC Chart.

4WD LOCKED TEMPORARILY - Displayed when the 4WD system is locked due to heat protection. In the locked mode the vehicle resists turning and binds up when driven on dry pavement. To exit the locked mode, stop the vehicle with the engine running and allow it to cool for 5 minutes.

Driving the vehicle in this mode will not damage the 4WD system. The system can return to normal mode without stopping the vehicle if driving conditions allow.

4WD DISABLED TEMPORARILY - Displayed when the 4WD system is disengaged due to heat protection. To exit the disabled mode, stop the vehicle with the engine running and allow it to cool. Driving the vehicle in this mode will not damage the 4WD system. This will change how the vehicle handles in off-road, snowy or wet conditions.

4WD AUTO RESTORED - Displayed when normal 4WD system function is restored after a heat protection system occurrence.