Principles of Operation

PRINCIPLES OF OPERATION

Pressing and releasing the ON switch turns the system on. Pressing and releasing the SET+ or SET- switch while the vehicle is traveling at the desired speed activates the system. The vehicle maintains the desired speed.

Tapping the SET+ or SET- buttons, while in the set mode respectively, increases or decreases the maintained vehicle speed by 2 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.

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:
- output shaft sensor (OSS)
- digital transmission range (TR) sensor
- speed control deactivator switch
- stoplamp switch
- speed control switches

The outputs from the PCM for the speed control system are the:
- instrument cluster
- throttle command

The speed control system does not require an electronic actuator for electronic throttle control (ETC) vehicles. Throttle position is completely controlled by the PCM through the electronic throttle body. Speed control electronics are contained entirely within the ETC subsystem.

When the speed control is active, the electronic actuator corrects for deviations in the actual vehicle speed by proportionally moving the throttle plate. The control electronics modulate the throttle to minimize error between actual vehicle speed and the desired speed.

The PCM strategy uses the engine control for smooth accelerations. In instances where the vehicle tends to exceed set speed, the PCM invokes an engine braking strategy to help maintain the desired vehicle speed.

The PCM sends a requested CAN vehicle speed control set speed message (enable/disable) whenever the speed control set indicator should be turned ON or OFF.

The driver commands the speed control system by pressing steering-wheel mounted switches. The steering wheel switches are hardwired to the PCM.

The speed control system operates in the following modes:
- STANDBY
- OFF
- VS CONTROL
- TAP UP
- TAP DOWN
- ACCEL
- DECEL
- RESUME

When the speed control is in the ON mode, and the PCM receives a SET+ or SET- switch input, the speed control system enters into the SET mode and maintains present vehicle speed (provided the vehicle speed is within the system operating range). When the PCM receives a SET+ switch input, the speed control system will accelerate the vehicle at approximately 1.5 mph/sec (on level roads). The speed control system continues to accelerate the vehicle until the switch is no longer pressed and then will maintain that vehicle speed. If the duration of the switch input is less than 640ms the speed control system will increase vehicle speed by 2 km/h (1 mph). When the system is in the standby mode, and a RESUME switch input is received, the speed control subsystem transitions into SET mode and modifies vehicle speed to resume the last SET vehicle speed, provided the speed control system has previously been in the SET mode subsequent to the key on last cycle.

When the PCM receives a SET- switch input, the speed control system will decrease vehicle speed at approximately 1.5 mph/sec (on level roads). Once the switch is no longer pressed, the speed control system ceases vehicle deceleration and maintains present vehicle speed. If the duration of the switch input is less than 640ms, the speed control system will decrease vehicle speed by 2 km/h (1 mph).

In the event of an OFF command or a deactivation request from any source, except the cancel switch, 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.

NOTE: The speedometer does not use the same signal as the speed control system.

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.