Cruise Control: Description and Operation

Speed Control

Petrol Engine Speed Control Component Location








Petrol Engine Speed Control, Control Diagram








Speed Control
The speed control system is integrated with the engine management system and uses fuelling intervention to automatically maintain a set vehicle speed. Once engaged, the system can also be used to accelerate the vehicle without using the accelerator pedal. The speed control system comprises the following components:
^ On/Off/Suspend switch
^ '+' and '-' (set/accelerate and decelerate)
^ Resume switch
^ Clock spring
^ Speed control warning lamp (in the instrument pack)

The speed control system also uses inputs from the brake pedal switch, the APP (accelerator pedal position) sensor, the ECM (engine control module) and the ABS (anti-lock brake system) control module.

The speed control is operated by the driver using only the steering wheel switches. When speed control is active, the ECM (engine control module) regulates the PWM (pulse width modulation) signals to the fuel injectors to adjust the fuel supply as required to maintain the set speed.

Control Switches





The speed control switches are located on the RH (right-hand) side of the steering wheel. The switches are connected via fly leads directly to the clock spring. All of the speed control switches are non-latching momentary switches.

The minimum set speed for speed control is 17 mph (27 km/h), the maximum set speed is 155 mph (250 km/h). Speed control is automatically switched off if the vehicle speed falls below 15 mph (24 km/h).

On/Suspend/Off Switch
The on/suspend/off switch controls the selection of speed control. When the ignition is in position II, a single press of the switch will activate the speed control system. A subsequent press of the switch activates the suspend mode, which temporarily switches off the speed system, but retains the previously set speed in the ECM (engine control module) memory. A third press of the switch switches off the whole speed control system.

Accelerate/Decelerate (+/-) Switches
When the speed control system is active, pressing the '+' switch set the controlled speed to the current road speed of the vehicle. Subsequent momentary presses of the switch increase the set road speed by 0.6 mph (1 km/h) with each press. If the switch is pressed and held the road speed will continue to increase until the switch is released.

Momentarily pressing the '-' switch, decreases the set speed by 0.6 mph (1 km/h) with each press. If the switch is pressed and held, the set speed is decreased until the switch is released.

Resume Switch
The resume switch re-activates the previously set speed after the speed control has been suspended by pressing the suspend switch or by depressing the brake pedal.