Principles of Operation

WARNING: This page is about a different car, the 2009 Ford Flex. However, it is still accessible from the selected car via links, so may be relevant.

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 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. Pressing the brake pedal puts the speed control system in 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.

Whenever the speed control system is engaged and active, a speed control indicator 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 pressed, an electrical signal is sent from the stoplamp switch to the PCM and the SJB to deactivate the speed control system. The SJB sends a message to the IC and the illuminated speed control indicator is turned off. Under increased brake pedal effort, the 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
Speed control switches
Stoplamp switch
Speed control deactivator switch
SJB messages

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

Speed control indicator lamp
Throttle command

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 strategy uses the throttle control for smooth accelerations.

The PCM sends a serial message over the Controller Area Network (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 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 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 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 is put into 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 48 km/h (30 mph)
Speed control switch is pressed or stuck longer than 2 minutes