Hill Descent Control

Hill descent control uses the ABS pump motor and HCU to provide vehicle speed control while descending a downhill grade, information from the Restraints Control Module (RCM) is used to determine whether or not the vehicle is on a downhill grade and wheel speed sensor information to determine vehicle speed. When the hill descent control switch is pressed, a ground signal is sent to the IPC indicating that the driver has activated the system. The IPC sends a message to the ABS module along the HS-CAN requesting system activation. The ABS module uses the input from the RCM and wheel speed sensors to determine the mode of operation (active, stand-by or deactivated). During a hill descent while the hill descent control system is activated, the driver sets vehicle speed through the use of the accelerator and brake pedals. Once the desired speed has been set, the system maintains that speed until: the vehicle is no longer on a downhill grade, the driver presses the switch again, vehicle speed exceeds 32 km/h (20 mph) or the system is disabled for cooling.

During periods of sustained use, the hill descent control system may automatically deactivate in order to cool the brake system. When this occurs, the system notifies the driver with a message in the message center and by sounding a warning chime. At this time the driver needs to provide brake and/or throttle control to maintain the desired descent speed. The system remains disabled until it has sufficiently cooled. The length of time needed for cooling varies depending on operating conditions.