Hill Descent Control (HDC)*1

Updated 08/06/2023

HDC can be compared to an automatic engine brake. When you release the accelerator on downhill gradients the car is normally braked by means of the engine striving for low engine idling speeds, so-called engine braking. But the steeper the road and the more load there is in the car, the faster the car rolls despite engine braking. In order to then reduce speed the driver has to assist using the foot brake.

Warning

HDC does not work in all situations but is designed merely as a supplementary aid.

The driver always bears ultimate responsibility for ensuring that the vehicle is driven safely.

HDC makes it possible to increase/reduce speed on steep downhill gradients, with a foot only on the accelerator pedal, without using the foot brake. The sensitivity of the accelerator pedal decreases and becomes more precise by means of the full actuation of the pedal being restricted to adjusting engine speed within a limited range. The brake system brakes itself and provides the car with a low and even speed, so allowing the driver to fully focus on steering.

HDC is particularly helpful on steep gradients with an uneven road surface and slippery sections. E.g. when launching a boat on a trailer from a ramp.

Function

HDC is engaged or disengaged using a switch on the centre console. An indicator lamp in the button illuminates when the function is switched on.

When HDC is operating this symbol illuminates and the combined instrument panel shows Hill descent control ON

The function only operates with gear 1 or reverse gear R - with automatic gearbox the combined instrument panel then shows the character 1 or R, see Automatic gearbox -- Geartronic *.

Note

HDC cannot be activated on an automatic gearbox when the gear selector is in position D.

Operation

HDC allows the car to roll at a maximum of 10 km/h forwards with engine braking and 7 km/h backwards. However, any speed within the gear's speed register can be selected using the accelerator pedal. When the accelerator pedal is released, the car is braked quickly to 10 or 7 km/h respectively, irrespective of the hill's gradient and without the need for the foot brake.

The brake lights come on automatically when the function is operating. The driver can brake or stop the car at any time by using the foot brake.

HDC is deactivated:

with the on/off button on the centre console
if a gear higher than 1 is selected on a manual gearbox
if a gear higher than 1 is selected on an automatic gearbox, or if the gear selector is moved to position D.

The function can be disengaged at any time. If it takes place on a steep downhill gradient then the braking effect will not release directly, but slowly instead.

Note

With HDC activated you may experience a delay between acceleration pedal activation and engine response.