Cruise Control: Description and Operation

Cruise Control Description and Operation

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions at speeds above 40 km/h (25 mph). Steep grades may cause variations in the selected vehicle speeds.

The following are the main components of the cruise control system:

* The accelerator pedal
* The cruise control switches
* The engine control module (ECM)
* The clutch pedal position (CPP) switch, if equipped with manual transmission
* The stop lamp switch
* The cruise control release switch
* The throttle actuator control (TAC) motor
* The vehicle speed sensor (VSS)

Cruise Control Engaged

The Cruise Control System will engage and adjust vehicle speeds, based on the activation of the following cruise control switches:

* On/Off
* + RES (resume/accel)
* - SET (set/coast)

The body control module (BCM) monitors the signal circuit of the cruise control switches. The BCM relays the cruise control switch status to the engine control module (ECM) via the GMLAN serial data circuit. The ECM uses the status of the cruise control switch to determine when to capture and maintain the vehicle speed. The ECM monitors the vehicle speed signal circuit in order to determine and the desired vehicle speed. The ECM uses the throttle actuator control (TAC) motor in order to maintain the vehicle speed. For further information on the TAC system, refer to Throttle Actuator Control (TAC) System Description in Computers and Control Systems - 2.2L (L61) or to Throttle Actuator Control (TAC) System Description in Computers and Control Systems - 2.4L. Ignition voltage is supplied to the cruise control switch from the 2-amp EPS fuse located in the integrated BCM fuse block. The cruise control function switches are arranged in a resistive ladder design, with each cruise control function switch having a different resistance value. The BCM detects a specific voltage value that is associated with any cruise control function switch being activated. When the normally open cruise control On/Off switch is turned ON, the switch closes and the BCM detects a predetermined voltage signal on the cruise control set/coast and resume/accel switch signal circuit. The BCM sends a GMLAN serial data message to the ECM indicating that the On/Off switch is active. Similarly, when the + RES switch or the - SET switch are pressed, the BCM detects the predetermined voltage signal on the cruise control set/coast and resume/accel switch signal circuit. To engage the cruise control system, ensure that the vehicle speed is above 40.2 km/h (25 mph), turn the cruise On/Off switch ON and momentarily press the - SET switch. The ECM will engage the cruise control system and record the vehicle speed. The ECM sends a GMLAN serial data message via the BCM to the driver information center (DIC) in order to display the CRUISE ENGAGED message. The - SET switch or the + RES switch will remain inactive when the BCM has not received the predetermined voltage signal from the On/Off switch. Pressing the accelerator pedal, while the cruise control system is engaged, will allow the driver to override the cruise control system in order to accelerate the vehicle beyond the current set vehicle speed. When the accelerator pedal is released, the vehicle will decelerate and resume the current set vehicle speed. The driver can also override the current set vehicle speed via the - SET switch and the + RES switch. When the cruise control system is engaged, pressing and holding the - SET switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating the cruise control system. When the - SET switch is released, the ECM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily pressing the - SET switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments for each time that the - SET is momentarily pressed, with a minimum vehicle speed of 37 km/h (23 mph). Pressing and holding the + RES switch, when the cruise control system is engaged, will allow the vehicle to accelerate to a greater vehicle speed than the current set vehicle speed. When the + RES switch is released, the ECM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily pressing the + RES switch will allow the vehicle to accelerate at 1.6 km/h (1 mph) increments for each time that the + RES switch is momentarily pressed, with the maximum acceleration total of 16 km/h (10 mph) over the current set vehicle speed. Momentarily pressing the + RES switch after the cruise control system has been disengaged by pressing the brake pedal, will recall the previous set vehicle speed that is recorded in the ECM.

Cruise Control Disengaged

The engine control module (ECM) disengages the cruise control operation based on the signals from the following switches:

* The stop lamp switch
* The cruise control release switch
* The clutch pedal position (CPP) switch (if equipped)
* The cruise control on/off switch

The cruise control release switch, the clutch pedal position (CPP) switch, and the stop lamp switch are used to disengage the cruise control system. The cruise control release switch and the stop lamp switch are mounted on the brake pedal bracket. When the brake pedal is applied, the normally closed cruise control release switch opens and the normally open stop lamp switch closes. The ECM detects a low signal voltage on the cruise control release switch signal circuit and a high signal voltage on the stop lamp switch signal circuit. When the clutch pedal is applied, the normally closed CPP switch opens and the ECM detects a low signal voltage on the CPP switch signal circuit. The vehicle speed stored in the memory of the ECM will be erased when the cruise control On/Off button is pressed, or the ignition switch is turned OFF.

The cruise control system will disengage when either the cruise control On/Off switch is switched OFF, or the ECM detects that a driver override function has been active for approximately 60 seconds.

When the cruise control system is disengaged, the ECM sends a GMLAN serial data message via the BCM to the driver information center (DIC) in order to turn OFF the CRUISE ENGAGED message.

Cruise Control Inhibited

The engine control module (ECM) inhibits the cruise control operation when any of the following conditions exist:

* A cruise control related DTC has been set.
* The vehicle speed is less than 40.2 km/h (25 mph).
* The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear.
* The engine RPM is too low.
* The engine RPM is too high, with fuel cut off.
* The vehicle speed is too high, with fuel cut off.
* The system voltage is not between 9-16 volts.
* The Antilock Brake System/Traction Control System is active for more than 2 seconds.