When the speed control system is activated, a selected vehicle speed between 48 and 201 km/h (30 and 125 mph) can be maintained without pressing the accelerator pedal. The speed control does not work at speeds below 48 km/h (30 mph).
The vehicle speed control system consists of the following components
- Speed control switch
- Speed control deactivator switch
- Stoplamp switch
- Speed control indicator
- Powertrain control module (PCM)
- Electronically controlled throttle
- Clockspring
Special Tools Illustration Tool Name Tool Number 73III Automotive Meter 105-R0057 or equivalent Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool. Restraint System Diagnostic Tool (2 required) 418-F395
Scheme 1
Scheme 2
Principles of Operation
The speed control system is controlled by the powertrain control module (PCM). The speed control system is designed to maintain a selected vehicle speed between 48 and 201 km/h (30 and 125 mph).
The speed control system is controlled by the steering wheel-mounted switches (ON, OFF, SET +/-, COAST, RESUME), 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 speed
- Tapping-up/tapping-down the vehicle speed
- Resuming the prior vehicle speed
- Coasting 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 COAST 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 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 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, the ignition switch is in the OFF position, 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 switch in the steering wheel.
The speed control deactivator 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 is illuminated.
The inputs to the PCM for the speed control system are the
- Transmission output shaft speed (OSS) sensor
- Digital transmission range (TR) sensor
- Speed control switch
- Stoplamp switch
- Speed control deactivator switch
- Accelerator pedal position sensor
- Parking brake
The outputs from the PCM for the speed control system are the
- Instrument cluster
- Throttle command
The speed control system throttle position is completely controlled by the PCM through the electronic throttle body (ETB). Speed control electronics are contained entirely within the electronic throttle control (ETC) subsystem.
When the speed control 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 message over the controller area network (CAN) vehicle speed control set speed status (enable/disable) to the instrument cluster 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 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 cluster telltale or message center messages are displayed when faults occur. Fault codes are logged by the PCM.
An ETC system fault causes the speed control system to be disabled and the ETC warning lamp illuminates, or a message center message is displayed.
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.
- A vehicle speed loss from set speed of greater than 10 mph occurs.
- The vehicle speed falls below the minimum allowable limit (48 km/h [30 mph]).
- The parking brake is applied.
- A speed control switch is pressed or stuck longer than 2 minutes.
Normal Operation
The powertrain control module (PCM) sends a signal through circuit VES10 (WH) to the speed control switch, which passes through the clockspring. The return signal is sent to the PCM through circuit RES08 (GN/BN) and the clockspring. When the brake pedal is applied, the smart junction box (SJB) sends a message to the PCM to deactivate the speed control, if engaged.
The speed control deactivator switch interrupts circuit CES09 (VT/OG) removing the voltage signal to the PCM when the brake pedal is applied. This is a redundant signal to the PCM.
Possible Causes
- PCM not configured for speed control
- Stoplamp switch
- Speed control switch
- Digital transmission range (TR) sensor
- Vehicle speed signal
- PCM
When the brake pedal is applied, the smart junction box (SJB) sends a message to the powertrain control module (PCM) to deactivate the speed control, if engaged.
The speed control deactivator switch interrupts circuit CES09 (VT/OG), by removing the voltage signal to the PCM when the brake pedal is applied. This is a redundant signal to the PCM.
DTC P1572 - sets when the PCM does not sense the proper sequence of the brake pedal input signal from both the stoplamp and deactivator switches when the brake pedal is pressed and released.
DTC P1703 - sets when there is an open or short in the deactivator switch circuits or when there is an open or short in the stoplamp circuits.
Possible Causes
- Fuse
- Circuit CBB42 (GN) open
- Circuit CES09 (VT/OG) open or short to voltage
- Circuit CCB08 (VT/WH) open
- Speed control deactivator switch
- PCM
The powertrain control module (PCM) sends a signal through circuit VES10 (WH) to the speed control switch, which passes through the clockspring. The return signal is sent to the PCM through circuit RES08 (GN/BN) and the clockspring.
DTC P0579 - sets when the speed control switch circuits are open, shorted to voltage or shorted to ground.
DTC P0581 - sets when the speed control switch circuits are shorted to voltage or open.
Possible Causes
- Circuit RES08 (GN/BN) open or short to voltage
- Circuit VES10 (WH) open, short to voltage or ground
- Clockspring
- Speed control switch
- PCM
See also:
• AUTOMATIC TRANSAXLE/TRANSMISSION - 5R55S