Principles of Operation

Cruise Control

Principles of Operation

The cruise control system is controlled by the PCM. The cruise control system is designed to maintain a selected vehicle speed between 40 km/h (25 mph) and the maximum limited vehicle speed. The cruise control system is controlled by the cruise control switches (ON/OFF, SET+, SET-, and CNCL, RSM) that are integrated into the LH steering wheel switch, and by the brake pedal. The cruise control switches are hardwired to the Steering Column Control Module (SCCM). The SCCM sends High Speed Controller Area Network (HS-CAN) network messages to the PCM to control the cruise control system.

The clockspring provides the electrical interface between the steering column wiring and the cruise control switches in the steering wheel.

The cruise control functions include:

- turning on the cruise 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 cruise control system.

Pressing and releasing the ON switch turns the cruise control system on. The cruise control indicator located in the Instrument Panel Cluster (IPC) illuminates amber to indicate that the cruise control system is in standby mode. Pressing and releasing the SET+ or SET- switch while the vehicle is traveling at the desired speed activates the cruise control system. The cruise control indicator illuminates green to indicate that the cruise control system is active.

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 cruise control system off. While the cruise control system is active, applying the brake pedal or pressing the CNCL/RES switch puts the cruise control system into the standby mode. Pressing the CNCL/RES switch, when the cruise 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 cruise 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 cruise control deactivator switch opens and removes the ground signal from the PCM input circuit, releasing the throttle.

The inputs to the PCM are:

- Output Shaft Speed (OSS) sensor
- Digital Transmission Range (TR) sensor
- Cruise control switch(es) (networked from SCCM)
- Cruise control deactivator switch (integral to the stoplamp switch)
- Stoplamp switch
- Accelerator Pedal Position (APP) sensor
- Vehicle speed (networked from ABS module)

The outputs of the PCM are:

- Cruise control indicator lamp request to the IPC
- Throttle command

For gasoline engines, the vehicle speed is controlled by the PCM through the Electronic Throttle Control (ETC) subsystem.

When the cruise 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.

For diesel engines, the vehicle speed is controlled by the PCM through the electronic control fuel delivery system.

In the event of an OFF command or a deactivation request from the cruise control deactivator switch, the cruise control system carries out a hard deactivation and immediately returns the throttle to the idle position.

The cruise control system provides self-diagnostics. Cruise control is disabled anytime an error is detected in the system. No IPC indicator or message center messages are displayed when faults occur. Fault codes are logged by the PCM or SCCM.

An ETC system fault also causes the cruise control system to be disabled. In this case, an ETC system powertrain malfunction (wrench) warning indicator is displayed.

Additionally, the following conditions cause the cruise control system to deactivate:

- Transmission gear selector in a position other than D, M or 2 (automatic transmission)
- Cruise 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)
- Cruise control switch pressed or stuck longer than 2 minutes
- ABS fault

Cruise Control Deactivation Event PIDs

The PCM has PIDs available, through the powertrain datalogger, that show what caused the last cruise control deactivation. The PCM has 24 cruise control deactivation event PIDs, identified as CRUISEOFF_00 through 24. The most recent deactivation event is always listed in the event PID. These PIDs display what caused the cruise control deactivation to trigger and can be a very useful tool when trying to identify the cause of a deactivation trigger.