Principles of Operation
Speed Control
Principles of Operation
NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).
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 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 button, 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 button is pressed, or if the current vehicle speed is below the minimum operational speed.
The clockspring provides the electrical interface between the steering column wiring and the speed control switches in the steering wheel.
The speed control deactivator switch (part of the stoplamp switch) is provided as an additional safety feature. When the brake pedal is applied, the speed control deactivator switch opens and removes the voltage signal from the PCM input circuit, deactivating the speed control system.
Whenever the speed control system is engaged and active, a speed control icon on the Instrument Cluster (IC) is illuminated.
The inputs to the PCM are:
- Output Shaft Speed (OSS) sensor
- Digital Transmission Range (TR) sensor
- Speed control switch
- Stoplamp switch
- Speed control deactivator switch (part of the stoplamp switch)
- Accelerator pedal position sensor
- SJB
The outputs of the PCM are:
- Speed control indicator lamp
- Throttle command
The PCM strategy uses the throttle control for smooth accelerations. The 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 vehicle speed and the desired speed.
The PCM sends a message over the High Speed Controller Area Network (HS-CAN) to the IC whenever the speed control indicator should be turned on or off.
In the event of an OFF switch command or a deactivation request from the 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 disables operation and sets 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.
An Electronic Throttle Control (ETC) system fault also causes the speed control system to be disabled. In this case, an ETC system warning indicator or 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)
- Speed control switch is pressed or stuck for longer than 2 minutes
- ABS fault