Ford Expedition 2003 Workshop Manual

2003 Expedition/Navigator Workshop Manual
SECTION 308-07A: Four Wheel Drive (4WD) Systems
DIAGNOSIS AND TESTING
Four Wheel Drive (4WD) Systems
Refer to Wiring Diagrams Cell 24, Engine Controls for schematic and connector information.
Refer to Wiring Diagrams Cell 23, Engine Controls for schematic and connector information.
Refer to Wiring Diagrams Cell 34, All-Wheel Drive for schematic and connector information.
Refer to Wiring Diagrams Cell 59, Generic Electronic Module for schematic and connector information.
Special Tool(s)
73III Automotive Meter
105-R0057 or equivalent
Worldwide Diagnostic System (WDS)
418-F224
New Generation STAR (NGS) Tester
418-F052 or equivalent scan tool
Vacuum Pump
014-R1054 or equivalent
Principles of Operation
The automatic four-wheel drive (A4WD) system is an electronic-shift 4WD system that allows the operator to choose between 2WD and three different 4WD modes. The
operator can switch between A4WD and 4WD HIGH modes at any speed. To engage or disengage 4WD LOW range, the vehicle speed must be less than 5 km/h (3.1
mph), the brake pedal must be pressed and the transmission must be in NEUTRAL.
Wheel slip is sensed using one axle shaft speed sensor on each axle. Based on throttle position and wheel slip, a pulse width modulated (PWM) signal is transmitted to
the transfer case clutch when a predetermined slip-threshold is exceeded.
The 4WD control module will provide the IVD brake system with current clutch duty cycle and whether or not IVD may command the clutch duty cycle.
The brake subsystem sends the following information signals to the 4WD system:
occurrences of brake events and failures (for additional information, refer to Section 206-09.)
steering wheel angle status (for additional information, refer to Section 206-09.)
average rear wheel speed (for additional information, refer to Section 206-09.)
average front wheel speed (for additional information, refer to Section 206-09.)
delta front wheel speeds (for additional information, refer to Section 206-09.)
A concern with any of the above listed brake system signals will affect operation of the 4WD system.
The throttle position output signal is provided to the 4WD control module from the powertrain control module (PCM). This signal is used by the 4WD control module in
controlling the 4WD clutch.
The shift motor sense plate, an integral part of the gearmotor encoder assembly, informs the 4WD control module of the transfer case position.
The digital transmission range (TR) sensor is located on the LH side of the transmission. This sensor informs the 4WD control module when the transmission is in
NEUTRAL.
The electric shift motor is mounted externally to the gearmotor encoder assembly at the rear of the transfer case. It drives a rotary cam which moves the mode fork and
range fork within the transfer case between the HIGH range (A4WD, 4WD HIGH) and 4WD LOW range positions.
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2003 Expedition/Navigator Workshop Manual
Procedure revision date: 04/13/2006
1/22/2010