Cruise Control: Description and Operation

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades may cause variations in the selected speeds. The electronic cruise control system has the capability to CRUISE, COAST, RESUME SPEED, ACCELERATE, and TAP-UP or TAP-DOWN.

The main parts of the cruise control system are:
^ The cruise control module assembly
^ The function control switches
^ The cruise control release switch
^ The stop lamp switch assembly
^ The vehicle speed sensor

The cruise control system uses the cruise control module assembly to maintain the desired vehicle cruise speed and operation. The cruise control module assembly has a controller and an electric stepper motor to vary the throttle in each different cruise control mode. Two components in the module assembly help to do this. The electronic controller and the electric stepper motor The controller monitors vehicle speed and operates the stepper motor. The stepper motor operates in response to the controller, to maintain the desired cruise speed. The stepper motor moves a strap that is attached to the cruise control cable which moves the throttle linkage. The cruise control module assembly contains a low speed limit which will prevent system engagement below a minimum speed of 40 km/h (25 mph). The module assembly is not serviceable.

The operation of the controller is controlled by the function control switches located on the steering wheel. The functional control switches include the ON/OFF, SET/COAST, R/A (resume/accelerate). The switch assemblies provide driver control of the cruise control system.

The release switch and the stoplamp switch are used to disengage the cruise control. A release switch assembly and a stoplamp switch assembly are mounted on the brake pedal bracket. To disengage the system the driver presses the brake pedal. The speed of the vehicle at brake actuation will be stored in the memory of the cruise module.

With cruise control, you can maintain a speed greater than 40 km/h (25 mph) without keeping your foot on the accelerator. When the driver turns OFF the ON/OFF switch or the ignition switch, the cruise control turns off. The vehicle speed stored in the memory of the cruise module will be lost.

Ignition 1 voltage is supplied from the cruise control fuse, to the cruise control module. The cruise control module is grounded to the chassis. When the cruise control ON/OFF switch is ON, ignition 1 voltage is applied to the ON switch signal circuit of the cruise control module. If the driver has not pressed the brake pedal, ignition positive voltage is supplied to the TCC Brake switch signal circuit of the cruise control module. When the driver presses the brake pedal, battery positive voltage is supplied from the stoplamp fuse, through the closed stoplamp switch to the stoplamp switch signal circuit of the cruise control module. When the SET/COAST switch is pressed, ignition positive voltage is applied to the set/coast switch signal circuit of the cruise control module. When pressing the R/A (RESUME/ACCELERATE) switch ignition positive voltage is applied to the resume/ accelerate switch signal circuit of the cruise control module.

The cruise control module receives a vehicle speed signal input from the Powertrain Control Module (PCM). In operation, the voltage varies between 0-5 volts.

The cruise engaged signal circuit sends a signal to the PCM when cruise is engaged. The PCM sends a message to the Instrument Panel Cluster (IPC) to turn on the cruise light. The cruise cancel signal circuit is used by the PCM to inhibit cruise control when conditions inconsistent with cruise operation are present.

The PCM will inhibit cruise control under the following conditions:
^ When the vehicle speed is less than 40 km/h (25 mph)
^ When PARK, REVERSE, NEUTRAL, or 1st gear is indicated
^ With low engine RPM
^ With high engine RPM (fuel cut-off)
^ When the vehicle speed is too high
^ When an over charged or under charged battery voltage condition exists
^ Antilock brake system/traction control system is active for more than 2 seconds
^ A 6 mph or more decrease in non-drive wheel speed in 0.4 seconds without seeing the extended brake travel contacts of the TCC/Brake switch transition.

If the PCM determines that any of the cruise control inhibit conditions are present, the PCM will disengage the cruise control by opening the cruise control inhibit signal circuit. If the cruise engaged signal, sent by the cruise control module to the PCM, indicates that the cruise control is still engaged after the PCM has requested that the cruise control disengage, the PCM sets a DTC.