HDC: Hill Descent Control
WARNING: This page does not describe the selected car, but rather 45 other vehicles, including the 2016 BMW M5, 2016 BMW 550i xDrive, 2016 BMW 550i, 2016 BMW 535i xDrive, and 2016 BMW 535i. However, it is still accessible from the selected car via links, so may be relevant.
During steep desecnts on low-traction road surfaces (sand, gravel, snow and ice) the engine's drag torque is not enough to maintain vehicle speed at a low, constant rate. Owing to its relatively low speed and the low-traction road surface, if the brakes are applied the vehicle will tend to pull to one side, despite ABS.
HDC employs selective braking intervention to consistently maintain the preset speed (maximum of 25 km/h) and simultaneously stabilize the vehicle in a process mirroring closed-loop control from DSC.