L322 Range Rover Engine Management System - V8 Cruise Control Overview
ENGINE MANAGEMENT SYSTEM – V8
18-2-52 DESCRIPTION AND OPERATION
Cruise Control
General
Cruise control functionality is fully integrated into the ECM and uses electric throttle 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 cruise control system consists of:
l
Cruise control master switch
l
+/- Speed switch
l
Resume switch
l
EMS ECU
l
Electric throttle.
The Controller Area Network (CAN) bus is used by the cruise control system for the exchange of data between the
ECM, EAT ECU, DSC ECU and instrument pack.
Cruise control is enabled when the master switch is pressed. Once enabled, the cruise control system is operated
using the steering wheel switches. The steering wheel switches output a serial data stream to the ECM, the ECM then
adjusts the electric throttle to maintain the vehicle at the set speed.
The cruise control warning lamp provides a visual indication of when the system is engaged.
Master Switch
The master switch controls a feed to the ECM to enable the system. The switch is a momentary contact push switch
on the left hand steering wheel switch pack.
Steering Wheel Switches
The steering wheel switches, SET+ and RES, are non latching push switches that engage and disengage cruise
control and adjust the set speed. While pressed, the switches supply a serial data stream to the ECM to adjust the
set speed.
ECM
The ECM receives serial data from the steering wheel switches, which are interpreted by the ECM to operate cruise
control. The ECM also controls the output of a cruise engaged signal to the EAT ECU.
The ECM incorporates a software module and associated components to enable cruise control operation by direct
control of the electric throttle. In addition to controlling the throttle, the software module monitors hardwired and CAN
bus inputs to the ECM and prevents or suspends cruise control operation when the vehicle is not in the correct driving
configuration.
While the master switch is selected off, only the OFF message can be transmitted. When the master switch is
selected on, the power feed from the switch enables the interface switches to send either the SET or RESUME
messages, depending on the inputs from the steering wheel switches and the cruise control status message from the
CAN bus. When the master switch is first switched on, the output of the RESUME message is automatically inhibited
until after the first engagement of cruise control.
When cruise control is engaged, the ECM outputs a signal on CAN to the EAT ECU to provide a cruise control
engaged signal. The EAT ECU uses the signal to switch between normal and cruise control modes of operation.
Brake Pedal Sensor
Outputs from the brake pedal sensor are supplied to the ECM to enable the system to detect when the brakes are
applied. The brake pedal sensor is a Hall effect sensor that produces two outputs. Both outputs should be 0 to 2 volts
while the brake pedal is released. When the brake pedal is pressed, the Brake Lamp Switch (BLS) output increases
to between 6 and battery volts, the Brake Lamp Test Switch (BLTS) output increases to between 10 and battery volts.