Cruise Control: Description and Operation
Speed Control
Petrol Engine Speed Control Component Location
Petrol Engine Speed Control, Control Diagram
NOTE:
A= Hardwired D= CAN
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:
- Suspend switch/Resume
- '+' and '-' (set/accelerate and decelerate)
- Resume switch
- Clock spring
- Speed control warning lamp (in the instrument cluster)
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 is active, the ECM (engine control module) regulates the engine torque to maintain the set speed.
CONTROL SWITCHES
The speed control switches are located on the LH 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 rocker switches. The minimum set speed for speed control is 18 mph (30 (km/h). Speed control is automatically suspended if the vehicle speed falls below 15 mph (24 km/h).
The speed control switches are resistive ladder type switches. There are three switches associated with speed control, two of which are for active speed control (where specified). The switches vary the resistance of a signal voltage sent to the ECM (engine control module). The switches receive a 5 volt reference supply which is varied in response to which switches are pressed.
Suspend/Resume Switch
The suspend/resume switch controls the selection of speed control. When the ignition is in position II, a press of the suspend switch will activate the suspend mode which temporarily switches off the speed control system, but retains the previously set speed in the ECM memory.
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.
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.