Four Wheel Drive (4WD) Systems

Four Wheel Drive (4WD) Systems
The 1-speed torque on demand (TOD) (Navigator) and 2-speed TOD (Expedition) four wheel drive (4WD) systems consist of the following:
^ 4WD mode select switch (MSS)
^ 4X4 control module
^ Integrated wheel ends (IWEs) solenoid
^ IWEs
^ 4WD mode indicators and messages in the instrument cluster (IC) message center
^ Transfer case assembly
^ Transfer case shift motor
^ Steering wheel angle (SWA) signal from ABS module via high-speed controller area network (HS-CAN)
^ Accelerator pedal position output from the PCM via HS-CAN
^ Wheel speed signals from the ABS via HS-CAN

Integrated Wheel End (IWE) System
The IWE system contains the following:
^ Vacuum reservoir
^ IWE solenoid
^ IWEs (spring loaded vacuum hubs)
^ Vacuum hoses
^ Check valve

The IWE system uses vacuum hubs that engage the front wheel hubs to the front halfshafts or disengage the front wheel hubs from the front halfshafts.

The IWE solenoid receives engine vacuum from the vacuum reservoir.

When the 4WD system is in two wheel drive (2WD) mode, the 4X4 control module supplies a ground path to the IWE solenoid to apply vacuum to the IWEs (disengaging the front hubs from the front halfshafts). In 4WD mode, the 4X4 control module does not supply the ground path to the IWE solenoid, vacuum is not applied to the IWEs and an internal spring keeps the front hubs engaged to the front halfshafts.