Hill Descent Control

WARNING: This page is about a different car, the 2018 Land Rover Discovery and 2017 Land Rover Discovery. However, it is still accessible from the selected car via links, so may be relevant.

Hill Descent Control (HDC) uses brake intervention to control vehicle speed and acceleration during low speed descents in off-road and low grip on-road conditions. Generally, equal pressure is applied to all four brakes, but pressure to individual brakes can be modified by the Anti-lock Brake System (ABS) and Dynamic Stability Control (DSC) functions to retain stability. Selection of the HDC function is controlled by the HDC switch and the Terrain Response® switchpack in the floor console. HDC operates in both high and low ranges, at vehicle speeds up to 50 km/h (31 mph).

WARNING: Incorrect use of the HDC function may compromise the stability of the vehicle, resulting in a dangerous and uncontrolled hill descent. Driving with the transmission in neutral while HDC is active will prevent engine braking from assisting the vehicle. The brakes will overheat and induce the HDC fade out strategy. In this condition there will be no control over the vehicle during a descent.

NOTE: With the HDC function selected, HDC is operative even when the transmission is in neutral. It is not recommended to drive the vehicle further than is absolutely necessary with HDC selected and the transmission in neutral.

HDC may be used in Drive (D), Reverse (R) and all CommandShift™ gears. When in D, the Transmission Control Module (TCM) will automatically select the most appropriate gear.

HDC can be selected at speeds up to 80 km/h (50 mph), but will only be enabled at speeds below 50 km/h (31 mph). When HDC is selected:

At speeds up to 50 km/h (31 mph), the HDC warning indicator in the Instrument Cluster (IC) is permanently illuminated if a valid gear is selected.
At speeds from between 50 to 80 km/h (31 to 50 mph) the HDC warning indicator flashes and a message advising that the speed is too high is displayed in the message center. If the HDC switch is pressed while vehicle speed is more than 80 km/h (50 mph), the HDC warning indicator will not illuminate and HDC will not be selected.
If the speed increases to 80 km/h (50 mph), the HDC function is switched off, the warning indicator is extinguished, a warning chime sounds and a message advising that HDC has been switched off is displayed in the message center.

When HDC is enabled, the ABS control module calculates a target deceleration value by comparing the set speed to the actual vehicle speed. The ABS control module then operates the HCU in the active braking mode as required to achieve and maintain the target speed.

During active braking for HDC, the ABS control module sends a message to the Body Control Module/Gateway Module (BCM/GW) to operate the stop lamps. For additional information, refer to: EXTERIOR LIGHTING .

Applying the foot brake during active braking may result in a pulse through the brake pedal.

The target speed varies between the minimum and maximum values for each gear and transmission range, depending on driver input with the speed control + and - switches. For additional information, refer to: SPEED CONTROL .