Hill Descent Control sometimes abbreviated to HDC is an electronically controlled
feature that assists drivers during certain off road manoeuvres by controlling the speed at which a vehicle proceeds down steep
This is a feature commonly found on sport utility vehicles/
crossovers and most other vehicles claiming to have any form of off roading ability.
Hill descent control by itself does not do much to add to a vehicle's off roading ability but it is usually used together
or alongside other off road features such as Terrain Response and
Hill Descent Control is a feature operated by the driver usually by pressing a switch on the dashboard, center console or
where other off road controls may be located. It does not activate automatically when the vehicle is proceeding downhill.
How it works is by allowing you to set a preset speed for the vehicle to proceed down a steep decline. As usual different
marques will have different speed ranges but it is usually between 3km/h to 30km/h (approximately 2mph to 19mph).
In order to keep the vehicle at the preset speed during a steep decline hill descent control uses the brakes, ABS and any other electronic aid or assistance that may
be equipped along with the brakes and it applies the brakes to each wheel individually.
This individual application of the brakes is what makes it suitable for off road downhill driving and separates the feature from
you just applying the brakes yourself.
Some vehicles may also use take control of the engine throttle and the transmission in addition
to the braking system. This method can take some of the stress of the brakes as the transmission will hold the a low gear such as first or
second to ensure that the vehicle is not free to just roll down the hill.
After pressing the hill descent control button, you may have to choose a desired speed. This is done in some vehicles by using the
buttons or switches for the cruise control.
Increasing or decreasing of the desired speed can be done using the buttons for the cruise control as well. In a similar manner
to cruise control, you can override the system by using the brakes or accelerator pedal.
The feature remains on for you to use again unless you turn it off. In some vehicles it may disengage once your vehicle crosses
a certain speed (usually above the speed range of that vehicle for hill descent control).
Other vehicles such as those under the Ford marque will maintain the speed you were travelling at when you set the hill
descent control and if you wish to increase or decrease the speed you would apply the accelerator or brakes pedal respectively
until your desired speed is attained and the vehicle would then remain at that speed.
Various marques may have different names for this feature such as Porsche Hill Control (PHC) for the Cayenne and Mercedes
Benz has Downhill Speed Regulation (DSR) for the ML/M-Class.