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 40 km/h (25 mph) and the maximum limited vehicle speed. The speed control system is controlled by the steering wheel mounted switches (ON, OFF, SET+, SET-, and RES), the stoplamp switch and the speed control deactivator switch (integral to the stoplamp switch). The steering wheel mounted switches are hardwired to the PCM through the clockspring.

The speed control functions include:

- turning on the speed control system
- setting and maintaining the desired vehicle speed
- accelerating the vehicle speed
- decelerating the vehicle speed
- turning off the vehicle speed control system
- canceling the speed control

Pressing and releasing the ON switch turns the speed control system on. Pressing and releasing the 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, respectively. If either switch is pressed and held, the vehicle speed continues to accelerate (SET+) or decelerate (SET-) until the switch is released.

Pressing and releasing the OFF switch, or switching the ignition switch to the OFF position, turns the speed control system off. Applying the brake pedal puts the speed control system into the standby mode. Pressing the RES switch when the speed control system is in the standby mode causes the vehicle to accelerate to the last set speed. The RES switch does not function if the OFF switch is pressed 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 clockspring provides the electrical interface between the steering column wiring and the speed control switch in the steering wheel.

When the brake pedal is applied, an electrical signal from the stoplamp switch is sent to the PCM to deactivate the speed control system. The speed control deactivator switch (integral to the stoplamp switch) is provided as an additional safety feature. Under increased brake pedal effort, the speed control deactivator switch opens and removes the voltage signal from the PCM input circuit, deactivating the speed control system.

The ABS module monitors brake pressure and also receives an electrical signal from the stoplamp switch. A fault in the ABS module can disable the speed control system.

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

The inputs to the PCM for the speed control system are the:

- Output Shaft Speed (OSS) sensor
- Digital Transmission Range (TR) sensor
- Speed control switch
- Stoplamp switch
- Speed control deactivator switch (integral to the stoplamp switch)
- Accelerator pedal position sensor

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

- 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 PCM.

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 actual and desired vehicle speed.

The PCM strategy uses the throttle control for smooth accelerations.

The PCM sends a serial message over the High Speed Controller Area Network (HS-CAN) to the IC to command the speed control telltale to be turned on or off.

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

The speed control system provides self-diagnostics. The speed control system will disable operation and set a PCM DTC if it detects certain faults. The IC does not indicate speed control faults with a telltale or message center message. Fault codes are logged by the PCM.

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

- The transmission gear selector is in a position other than D or OD.
- The speed control set speed is over-ridden with the accelerator pedal for longer than 5 minutes.
- Vehicle speed loss from set speed of greater than 16 km/h (10 mph) occurs.
- The vehicle speed falls below the minimum allowable limit (40 km/h [25 mph]).
- A speed control switch is pressed or stuck longer than 2 minutes.
- ABS system fault