Speed Control - Principals of Operation

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SPEED CONTROL - HYBRID

See the Tribute Wiring Diagram for schematic information.

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, and the speed control deactivator switch. The steering wheel mounted switches are hardwired to the PCM through the clockspring.
The speed control switch functions include:

- Turning on the speed control system
- Setting and maintaining the desired vehicle speed
- Accelerating the vehicle speed
- Decelerating the vehicle speed
- Resuming the prior vehicle speed.
- Turning off the vehicle speed control system
- Canceling the speed control
Pressing and releasing the ON switch turns the system on. Pressing and releasing the SET+ or SET- switch while the vehicle is traveling, sets the desired speed.Tapping the SET+ or SET- buttons, while in the set mode, increases or decreases the maintained vehicle speed by 1.6 km/h (1 mph) per tap for US instrument clusters, or 2.0 km/h (1.24 mph) per tap for metric instrument clusters. 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 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 RESUME switch when the speed control system is in the standby mode causes the vehicle to accelerate to the last set speed. The RESUME 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.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 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 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:

- Transmission Range (TR) sensor
- Speed control switch(es)
- Stoplamp switch
- Speed control deactivator switch
- Accelerator pedal position sensorThe outputs from 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 electric traction motor is powering the vehicle and the speed control is active, the electronic actuator corrects for deviations in the actual vehicle speed by proportionally applying wheel torque. The control electronics modulate the wheel torque to minimize error between the actual vehicle speed and the desired speed.The PCM strategy uses the powertrain control for smooth accelerations.The PCM sends a message over the high speed controller area network (HS-CAN) to the 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 except a brake pedal tap, the system carries out a hard deactivation and immediately returns control to the accelerator pedal.The ABS module monitors brake pressure and also receives the stoplamp switch input from the smart junction box (SJB) along the HS-CAN bus. A fault in the ABS module can disable the speed control system.The speed control system provides self-diagnostics. The 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 electronically-controlled throttle system fault also causes the speed control system to be disabled and a warning telltale (wrench light) 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 40 km/h (25 mph)
- Parking brake is applied
- Speed control switch is pressed or stuck for longer than 2 minutes
- Traction control event
- ABS system fault