Cruise Control: Description and Operation

Speed Control

COMPONENT LOCATION









OVERVIEW
The speed control system maintains a set speed selected by the driver until operation is suspended or cancelled by a further input from the driver and is controlled by the ECM.
The speed control system comprises the following components:
- A set +/- switch
- A RESUME switch
- A CANCEL switch.
The system also uses the following:
- The ECM
- The stoplamp switch.
- The APP sensor
The ECM controls the set speed by modifying engine speed/torque and requesting gear changes from the transmission (automatic variants only).
The speed control system also uses inputs from the brake pedal switch, the APP sensor, the ECM and the ABS control module.
The speed control is operated by the driver using only the steering wheel switches. When speed is active, the ECM regulates the PWM signals to the fuel injectors to adjust the fuel supply as required to maintain the set speed.
During speed control operation, the ECM controls vehicle speed by adjusting fuel injection duration and timing. When the accelerator pedal is pressed with speed control active, the ECM outputs a calculated throttle angle signal in place of the actual throttle angle signals produced by the APP sensor. The calculated throttle angle is derived from fuel demand.

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 the speed control switches are non-latching momentary rocker switches. The minimum set speed 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 rocker switches associated with speed control, two of which are for adaptive speed control (where specified). The switches vary the resistance of a signal voltage sent to the ECM. The switches receive a 5 volt reference supply. The ECM measures the returned voltage to determine which switch has been pressed.

Suspend Switch
The suspend/resume switch controls the selection of speed control. When the ignition is in position II, a single press of the suspend switch will activate the suspend mode. This temporarily switches off the speed control system, but retains the previously set speed in the ECM memory.

Resume Switch
A second press of the 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.

Set Speed/Increase/Decrease Speed (+/-) Switches
When the speed control system is active, pressing the '+' switch sets the controlled speed to the current road speed of the vehicle. Subsequent momentary presses of the switch increases the set road speed by 0.6 mph (1 km/h). 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). If the switch is pressed and held, the set speed is decreased until the switch is released.

CONTROL DIAGRAM

NOTE:
A = Hardwired; D = High speed CAN bus