You said in your original message that you were going down a hill, not on level ground. Nevertheless, on level ground or not, the X5 will NOT give power to the wheels with HDC activated unless you step on the accelerator. There is some power from the idle engine as EspoX5 explained in his post... but for the record, the only computer on board the X5 which will give power to the wheels is perhaps the cruise control system, NOT the HDC. HDC simply is a controlled braking method.