Cruise Control Description and Operation (Conventional Cruise Control)

CRUISE CONTROL DESCRIPTION AND OPERATION (CONVENTIONAL CRUISE CONTROL)

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 brake pedal position (BPP) sensor
- The body control module (BCM)
- The cruise control switches
- The engine control module (ECM)
- 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, which are located on the steering wheel:
- The on/off switch
- The + RES switch
- The - SET switch

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 the desired vehicle speed. The ECM uses the TAC motor in order to maintain the vehicle speed. For further information on the TAC System, refer to Throttle Actuator Control (TAC) System Description for the 4.6L engine.

Voltage is supplied to the cruise control switch from the steering wheel control switch reference voltage circuit supplied by the BCM. The cruise control 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 the cruise control function switch being activated. When the normally open cruise control On/Off switch is turned ON, the switch closes and the BCM supplies a ground to the cruise control switch ON indicator circuit as it becomes illuminated. The BCM sends a GMLAN serial data message to the ECM indicating that the On/Off switch is active. Similarly, when the normally open + RES switch or the normally open - SET switch are pressed, the switch closes and the BCM detects the predetermined voltage signal on the - SET switch and the + RES switch signal circuit. The BCM sends a GMLAN serial data message to the ECM indicating that the + RES switch or the - SET switch is active. To engage the Cruise Control System, ensure that the vehicle speed is above 40.2 km/h (25 mph), and then turn the 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 to the driver information center (DIC) in order to illuminate the CRUISE SET TO ### message. The ECM sends a GMLAN serial data message to the instrument panel cluster (IPC) in order to illuminate the Cruise Engaged indicator in the IPC. The - SET switch and 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 - SET switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments for each time that the - SET switch 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 activating the + RES switch will recall the previous vehicle speed, after the Cruise Control System is disengaged by pressing the brake pedal or by activating the CANCEL switch.

Cruise Control Disengaged
The engine control module (ECM) disengages the cruise control operation based on the signals from the following switches:
- The brake pedal position (BPP) sensor
- The cruise control On/Off switch
- The cruise control cancel switch

The body control module (BCM) determines when the cruise control cancel switch is activated. When the normally open cancel switch is closed, the BCM detects the predetermined voltage signal on the cruise control function switch circuit. The BCM sends a GMLAN serial data message to the ECM in order to disengage the cruise control system.

The BPP sensor is mounted on the brake pedal bracket. Pressing the brake pedal while the cruise control is engaged will disengage the Cruise Control system. The BCM monitors the BPP sensor signal circuit as the voltage signal increases, while the pedal reaches the fully applied position. The BCM sends a GMLAN serial data message to the ECM indicating the position of the brake pedal. For more information on the BPP sensor, refer to Exterior Lighting Systems Description and Operation and to Brake Pedal Position Sensor Calibration.

The Cruise Control System will also disengage when one of the following conditions exist:
- The cruise control On/Off switch is switched OFF.
- The ECM detects that a drive override function has been active for approximately 60 seconds.

When the Cruise Control System has been disengaged, the ECM sends a GMLAN serial data message to the instrument panel cluster (IPC) in order to turn OFF the Cruise Engaged indicator, and to the drive information center (DIC) in order to turn OFF the CRUISE SET TO ### message. The vehicle speed stored in the memory of the ECM will be erased when the cruise control On/Off button is turned OFF, or the ignition switch is turned OFF.

Cruise Control Inhibited
The engine control module (ECM) inhibits the cruise control operation when any of the following conditions exist:
- The ECM has not detected a brake pedal activation from the body control module (BCM).
- A Cruise Control System 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.
- The vehicle speed is too high.
- The system voltage is not between 9-16 volts.
- The Antilock Brake System (ABS)/Traction Control System (TCS) is active for more than 2 seconds.