Four Wheel Drive (4WD) Systems

Four Wheel Drive (4WD) Systems

The 1-speed torque on demand (TOD) (Navigator) and 2-speed torque on demand (TOD) (Expedition) 4 wheel drive (4WD) systems consist of the following:
^ 4WD mode select switch (MSS)
^ 4WD control module
^ Integrated wheel ends (IWE) solenoid
^ IWEs
^ 4WD mode indicators and messages in the instrument cluster message center
^ Transfer case assembly
^ Transfer case shift motor
^ Steering wheel angle (SWA) signal from anti-lock brake system (ABS) module
^ Accelerator pedal position output from the powertrain control module (PCM)
^ Wheel speed signals from the anti-lock brake system (ABS)

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