Principles of Operation

Speed Control

Principles of Operation

The speed control system is controlled by the PCM. The speed control system is designed to maintain a selected vehicle speed between 48 km/h (30 mph) and the maximum limited vehicle speed. The speed control system is controlled by the steering wheel mounted switches (ON, OFF, SET+, SET- and RESUME), deactivator switch and the brake pedal. The steering wheel mounted switches are hardwired to the PCM.

The speed control functions include:

- turning on the speed control system.
- setting and maintaining the desired vehicle speed.
- accelerating the vehicle to a higher speed.
- decelerating down to a lower speed.
- tapping-up/tapping-down the vehicle speed.
- resuming the prior vehicle speed.
- turning off the vehicle speed control system.

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

Tapping the SET+ or the SET- switch while in the set mode increases or decreases the maintained vehicle speed by 1.6 km/h (1 mph) per tap. If the respective switch is pressed and held, the vehicle speed continues to accelerate or decelerate until the switch is released.

Pressing and releasing the OFF switch, or turning the ignition switch to the OFF position, turns the speed control system off. Pressing the brake pedal puts the speed control system into the standby mode. Pressing the RESUME switch, when the speed control system is in the standby mode causes the vehicle to accelerate to the last set speed. Resume does not function if the OFF switch 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 icon on the Instrument Cluster (IC) is illuminated.

The speed control deactivator switch is provided as an additional safety feature. When the brake pedal is pressed, an electrical signal is sent from the stoplamp switch to the ABS module. A message is sent to the PCM indicating the brake pedal is applied through the High Speed Controller Area Network (HS-CAN). When the PCM receives this message, the PCM releases the throttle. Under increased brake pedal effort, the speed control deactivator switch opens and removes the voltage from the PCM input circuit, releasing the throttle.

The clockspring provides the electrical interface between the steering column wiring and the speed control switch in the steering wheel.

The inputs to the PCM are:

- Transmission Output Shaft Speed (OSS) sensor
- Digital Transmission Range (TR) sensor
- Speed control switch
- Stoplamp switch
- Speed control deactivator switch
- ABS module message

The outputs of the PCM for the speed control system are:

- Speed control indicator lamp
- Throttle command

The speed control system throttle position is completely controlled by the PCM through the electronically controlled throttle body. Speed control electronics are contained entirely within the Electronic Throttle Control (ETC) subsystem.

When the speed control system 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 the 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 to help maintain the desired vehicle set speed.

The PCM sends a serial message over the Controller Area Network (CAN) to the Instrument Cluster (IC) whenever the speed control telltale should be turned on or off.

In the event of an off command or a deactivation request from any source, the speed control system carries out a hard deactivation and immediately returns the throttle to the idle position.

The speed control system provides self-diagnostics. Speed control is disabled anytime an error is detected in the system. No IC telltale or message center messages are displayed when faults occur. Fault codes are logged by the PCM.

An ETC system fault also causes the speed control system to be disabled.

In this case, an ETC system warning indicator or a message center message is displayed.

Additionally, the following conditions cause the speed control system to deactivate:

- Transmission gear selector in a position other than D or OD
- Speed control set speed is over-ridden with the accelerator pedal for a period longer than 5 minutes
- Vehicle speed loss from set speed of greater than 16 km/h (10 mph) occurs
- Vehicle speed falls below the minimum allowable limit of 48 km/h (30 mph)
- Speed control switch is pressed or stuck longer than 2 minutes