Principles of Operation

WARNING: This page is about a different car, the 2003 Ford Windstar. However, it is still accessible from the selected car via links, so may be relevant.

The speed control system is designed to maintain a selected vehicle speed between 48 and 200 km/h (30 and 125 mph).

Whenever the system is engaged and active, a speed control set indicator will be illuminated in the instrument cluster.

The brake pedal position (BPP) switch is normally open. When the brake pedal is applied with the speed control system engaged, the BPP switch closes to battery voltage, putting the speed control in stand-by mode.

The electronic stepper motor (internal to the speed control servo) is controlled by turning the three phases of the motor on and off in sequence. The sequence determines the motor direction (open throttle, closed throttle) based on vehicle speed.

NOTE: The deactivator switch is provided as an additional safety feature. Normally, when the brake pedal is pressed and the BPP switch is closed, a message from the standard corporate protocol (SCP) link to the speed control servo will deactivate the system. Under increased brake pedal effort, the deactivator switch will open and remove power to the speed control servo clutch, releasing the throttle independently of the primary deactivation or BPP switch.

NOTE: The air bag sliding contact provides the electrical interface between the steering column wiring and the speed control switches in the steering wheel.

The inputs to the speed control servo are the:

SCP link. The speed control servo communicates with other control modules using the SCP link. The vehicle speed, brake pedal depressed (within 1-10 mm travel), throttle position, rpm and PRNDL status are retrieved by the speed control servo from the SCP link.
speed control switches.
deactivator switch.

The outputs of the speed control servo are the:

SCP link. The speed control servo sends an output message through the SCP link to indicate whether the speed control system is ON, OFF, ENGAGED or DISENGAGED.
speed control cable controlling the throttle position.