Cruise Control: Description and Operation
SPEED CONTROLPrinciples of operation
The speed control system is controlled by the powertrain control module (PCM). The speed control system is designed to maintain a selected vehicle speed between 48 and 200 km/h (30 and 124 mph).
The speed control system is controlled by the steering wheel-mounted switches (ON, OFF, SET+ [ACCEL], SET- [COAST], RESUME, and CANCEL), and the brake pedal. The steering wheel-mounted switches are hardwired to the PCM.
The speed control functions include:
- turn on the speed control system
- set and maintain the desired vehicle speed
- accelerate the vehicle speed
- coast down to a lower speed
- tap-up/tap-down the vehicle speed
- resume the prior vehicle speed
- turn off the vehicle speed control system
- cancel the speed control
Pressing and releasing the ON switch turns the system on. Pressing and releasing the SET+ (ACCEL) or SET- (COAST) switch while the vehicle is traveling at the desired speed activates the system.
Tapping the SET+ (ACCEL) or SET- (COAST) buttons, while in the set mode respectively, increases or decreases the maintained vehicle speed by 1.6 km/h (1 mph) per tap. If the respective button is pressed and held, the vehicle speed continues to accelerate or decelerate until the button is released. If the duration of the switch input is less than 640 ms the speed control system will increase vehicle speed by 1.6 km/h (1 mph).
Pressing and releasing the OFF switch, or positioning the ignition switch in the OFF position, turns the speed control off. Pressing the brake pedal or pressing the CANCEL button puts the system in the STANDBY mode. Pressing the RESUME button, when the system is in STANDBY mode causes the vehicle to accelerate until the last set speed is resumed. Resume does not function if the OFF button is pressed, the ignition switch is in the OFF position, or if the current vehicle speed is below the minimum operational speed.
Whenever the speed control system is engaged and active, a speed control illuminator is set.
The inputs to the PCM for the speed control system are the:
- anti-lock brake system (ABS) module
- digital transmission range (TR) sensor
- speed control deactivator switch
- brake pedal position (BPP) switch
- speed control switches
- throttle position sensor (TPS)
The outputs from the PCM for the speed control system are the:
- instrument cluster
- throttle command
The speed control system throttle position is completely controlled by the PCM through the electronic throttle stepper motor. Speed control electronics are contained entirely within the electronic throttle control (ETC) subsystem.
When the speed control is active, the PCM corrects for deviations in the actual vehicle speed by proportionally moving the throttle plate. The PCM modulates the throttle to minimize error between actual vehicle speed and the desired speed.
The PCM strategy uses the throttle control for smooth accelerations. In instances where the vehicle tends to exceed the set speed, the PCM invokes an engine braking strategy and the transmission downshifts to help maintain the desired vehicle speed.
The PCM sends a serial message over the controlled area network (CAN) vehicle speed control set speed status (enable/disable) to the instrument cluster whenever the speed control set telltale should be turned ON or OFF.
In the event of an OFF command or a deactivation request from any source, except the cancel switch and brake pedal tap, the system will carry out a hard deactivation and immediately return the throttle to the idle position.
In the event of CANCEL switch input, the system will deactivate and return the throttle to the idle position at a smooth and controlled rate.
The speed control system provides self-diagnostics. Speed control is disabled anytime an error is detected in the system. No cluster telltale or message center messages are displayed when faults occur. Fault codes will be logged by the PCM.