Operation CHARM: Car repair manuals for everyone.

Principles of Operation (How Does It Work?)

The speed control system is designed to maintain 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 closed to ground. 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.

NOTE:
^ A redundant brake deactivator switch is provided as an additional safety feature.
^ The speed control module is integral to the speed control servo.

Normally, when the brake pedal is depressed, the speed control module deactivates the speed control system. Under increased brake pedal effort, the deactivator switch, a normally closed switch, will open and remove power to the speed control servo clutch, releasing the throttle independently of the speed control module.

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:
^ vehicle speed signal
^ speed control switches
^ brake pedal position (BPP) switch
^ Clutch Pedal Position (CPP) switch
^ deactivator switch

The outputs of the speed control servo are the:
^ speed control indicator
^ speed control cable controlled throttle position