Cruise Control Operation

Cruise Control Operation

General

When the ignition is switched on, the interface ECU receives a power feed from the main relay and initialises the MFL serial link to the ECM. The ECM is in the normal fuelling mode and outputs the cruise control inactive message on the CAN bus. The interface ECU ignores inputs from the steering wheel switches.

When the master switch is pressed, the LED in the master switch illuminates and a second power feed is connected to the interface ECU to enable the system.

Engagement

Cruise control is engaged by pressing the SET+ steering wheel switch. On receipt of the input from the SET+ switch, the interface ECU outputs a SET MFL message. Provided the vehicle is in the correct driving configuration, when the ECM receives the SET message it stores the current vehicle speed in memory as the set speed. The ECM then adjusts the throttle as necessary to maintain the vehicle at the set speed, and changes the CAN bus message of cruise control status to active.

The vehicle is in the correct driving configuration, when: l The brakes are off. l The gearbox is in drive. l The vehicle is moving at a road speed between 22 and 125 mph (35 and 200 km/h). l Electronic Traction Control (ETC) is not active.

On receipt of the cruise control active message on the CAN bus, the instrument pack illuminates the cruise control warning lamp and the interface ECU outputs the hardwired cruise control engaged signal to the EAT ECU. On receipt of the cruise control engaged signal, the EAT ECU adopts the cruise control mode, which uses a gear change map less sensitive to changes of accelerator pedal position, to prevent unnecessary gear changes. This improves operating refinement for a minor loss of performance.

Acceleration

While cruise control is engaged, the vehicle can be accelerated using either the SET+ switch or the accelerator pedal. Each momentary press (less than 0.5 second) of the SET+ switch causes the interface ECU to output a SET MFL message to the ECM, which then increments the set speed by 0.6 mph (1 km/h) and accelerates the vehicle to the new set speed. If the switch is held on, the interface ECU repeatedly sends the SET MFL message until the switch is released. While it receives the messages, the ECM keeps incrementing the stored set speed and accelerating the vehicle. When the switch is released and the messages stop, the ECM adopts the increased vehicle speed as the new set speed.

If the accelerator pedal is used to accelerate the vehicle, the ECM reverts to normal throttle control when it detects the demand from the accelerator pedal sensor exceeds that of the current throttle setting. Provided the demand from the accelerator pedal sensor does not increase vehicle speed by more than 10 mph (16 km/h) above the set speed, for more than 30 seconds, cruise control remains engaged and the set speed is resumed once the accelerator pedal is released. If the SET+ switch is pressed before the accelerator pedal is released, the higher speed is adopted as the new set speed.

Suspend/Resume

Cruise control can be manually suspended and resumed (at the previous set speed) using the RES steering wheel switch. The ECM automatically suspends cruise control if one of the conditions required to enable the system is no longer present, e.g. the brakes are applied. Cruise control is also automatically suspended by the ECM if: l The vehicle speed increases to more than 10 mph (16 km/h) above the set speed for more than 30 seconds, e.g. when travelling downhill or using the accelerator pedal to override cruise control. l Engine speed increases too rapidly, e.g. if their is a fault in the gearbox or the gearbox goes into neutral. l The vehicle decelerates too rapidly, e.g. when the brakes are applied.