Like other shave said. It holds for a few seconds only, and of course only for an uphill start, not a downhill one. A good test.. find the steepest hill in your area. Pull up, with foot on brake. Apply the handbrake. Release the foot brake. about 2 seconds later, the rear end will raise up as the HAC releases. In this video, I talk to you about hill start assist. It is an option that is available on many modern cars with manual transmissions, and basically prevents Hill start assist system. Hill start assist keeps the brake engaged briefly to help prevent the vehicle from rolling on inclines as you move your foot from the brake pedal to the accelerator. Put the transmission into D, S, or L when facing uphill, or R when facing downhill, then release the brake pedal. Detail your speed on steep downhill gradients and. makes it even easier to control your BMW's. handling under these conditions. The vehicle. then moves slightly faster than double walking. speed without the driver needing to intervene. HDC can be activated as long as you are driving. under approx. 20 mph or 35 km/h. How Does Hill Holder Work? Hill start assist works with the help of various sensors in the vehicle. There are different ways in which this technology can be implemented. The ways in which hill start assist is activated are as follows: 1. Clutch Detection. One of the most common methods used in manual transmission vehicles is clutch sensing. This is particularly annoying because I have no real feel for how much load the engine is going to be under until it releases, and obviously different inclines are going to put a different amount of load on it. So I just have to guess how much throttle to give until it let's me go. So today I stalled for the first time on a steep hill. dustyjoe. Hill Assist Control is activated by pushing the brake pedal harder after stopping when the vehicle is in a forward gear. It will apply the brakes for up to two seconds after the brake pedal is released, which should prevent the vehicle from rolling backwards. Works very well and you soon get used to it. Sensors. Actuators. What does "perception" mean in relation to hill start assist? The sensors detect that the vehicle is on a slope. What will happen when hill start system has reached its maximum hold time? The vehicle will begin to roll back as the system stops operating. When does hill start assist work automatically? q3Qvr.