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 RESUME), the stoplamp switch, the clutch pedal speed control deactivator switch (manual transaxle), and the speed control deactivator switch (part of 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.
- coasting down to a lower 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 respectively, 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. Applying 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.

The clutch pedal speed control deactivator switch is used on vehicles equipped with a manual transaxle. When the clutch pedal is applied with the vehicle speed control system engaged, the normally open switch closes and signals the PCM to deactivate the speed control.

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. Normally, when the brake pedal is applied, an electrical signal from the stoplamp circuit to the PCM deactivates the system. 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 switches in the steering wheel.

The inputs to the PCM are:

- Output Shaft Speed (OSS) sensor
- Digital Transmission Range (TR) sensor (automatic transaxle)
- Speed control switch(es)
- Clutch pedal speed control deactivator switch (manual transaxle)
- Speed control deactivator switch (part of the stoplamp switch)
- Stoplamp switch

The outputs of the PCM 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 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 the actual vehicle speed and the desired 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 the speed control deactivator switch, 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. 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 cause the speed control system to deactivate:

- Transmission gear selector in a position other than D or OD (automatic transaxle)
- Clutch pedal is pressed (manual transaxle)
- The 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 40 km/h (25 mph)
- Speed control switch pressed or stuck longer than 2 minutes
- ABS system fault