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 roadway and the more load in the car, the faster the car coasts despite engine braking - the HDC function compensates for this with automatic brake intervention.

General information on HDC

The function makes it possible to increase/reduce speed on steep downhill gradients, with a foot only on the accelerator pedal, without using the footbrake. 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.

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.

Function

HDC is activated or deactivated with one of the centre console's switches. The lamp within it illuminates when the function is activated.

When HDC is working normally the combined instrument panel's symbol illuminates combined with the text message Hill descent control ON.

The function only operates in first gear position and in reverse gear. For an automatic gearbox, gear position 1 must be selected, which is shown with the figure 1 in the combined instrument panel, see Automatic gearbox - Geartronic *.

Note

HDC cannot be activated on an automatic gearbox 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 footbrake.

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 footbrake.

HDC is deactivated:

with the centre console's On/Off button
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.