In a BMW automobile, HDC stands for Hill Descent Control. It is a downhill driving assistant that BMW has implemented in order to assist the driver by automatically controlling the speed when descending steep hills. When the HDC system is activated, it will slow your vehicle to a speed equivalent to the speed of a person walking. It does so without the use of the brakes and is activated by the driver when necessary. Knowing when to use HDC and how it works can be a helpful understanding as a vehicle operator and can help you feel more focused and comfortable when driving you BMW on steep terrain.
HDC systems were originally created for off-road vehicles in order to allow the driver’s full attention to be on the steering of the vehicle. When driving on steep downhill gradients with loose or uneven surfaces, it can be hard to focus on both steering and proper braking at the same time and can sometimes result in loss of control of the vehicle completely. The HDC system is in place to take the stress off you and your brakes so full attention can be on steering. You can think of it as extremely low-speed cruise control that you use on really rough, downhill terrain.
HDC systems only work in four-wheel drive vehicles with an ABS (anti-lock braking system). This is because the HDC system uses ABS to control the speed of each wheel. Since the HDC system has access to each wheel independently through ABS, it is able to maintain traction by locking up or releasing individual wheels when necessary. This takes away the task the driver usually would have downshifting and braking to descend the hill.
Hill descent control can only be activated at speeds below 22 mph (35 km/h) and once it is activated it will slow the vehicle to about walking speed and keep it there until deactivated. It is important to note that since the system does not use the brakes during this time if you do engage the brakes it will put the system into standby until you reactivate it.
When HDC is working properly, you do still have the ability to change the speed of the descent slightly. To do this, you will use the rocker switch of the cruise control on your steering wheel. The range of speeds HDC can function in is between 4 mph (6km/h) and 15 mph (25 km/h). To accelerate gradually, simply press the rocker switch up until you feel resistance. If you press the rocker switch up past its resistance point, your vehicle’s speed will increase while the switch is being pressed. You will do the same when lowering the speed by pressing the rocker switch down. Some variations in speed will occur when using HDC in reverse.
If your BMW is equipped with an HDC system, there will be a button with the image of a vehicle going downhill with a speedometer with an arrow pointing forward above the vehicle. Once you’ve pressed this button, there should be LED lights above it that illuminate. In order to be activated, your vehicle will have to either be in drive or reverse and going below 22 mph (35 km/h). If those criteria are not met, HDC will not engage. When the system is in use, your vehicle’s brake lights will also be engaged to warn any drivers behind you that your speed has lowered.
On your instrument cluster, there will be a light depicting a vehicle going downhill with the selected speed next to it. When HDC is engaged, the light will be green and then turn orange when the system is on standby. Your vehicle’s HDC system will go into standby mode when you are actively using your accelerator or gas pedal. Once you reach a speed over 37 mph (60 km/h) the HDC system will automatically deactivate. You can also deactivate your vehicle’s HDC system by simply pressing the button again. You’ll know it is off when the LED light above it is no longer illuminated.
Like any other part of our vehicle, sometimes the HDC system needs to be serviced in order to function properly. If there is an issue, your vehicle will alert you in the gauge cluster with a light to check the HDC system. It is recommended that you take your BMW to a trusted mechanic to ensure things are not missed when examining the vehicle and the root of the issue is properly addressed. If you live in or around Louisville, KY, then consider consulting the experts at St. Matthews Import with any and all questions regarding your BMW.
* BMW F26 X4 image credit goes to: DarthArt.