Generally speaking it is the responsibility of the driver behind to maintain a safe distance and react appropriately if the vehicle in front comes to a sudden halt, so if a rear-end collision occurs the following driver is held responsible. However, if the car in front has stopped for no reason liability may not be as clear cut, but as far as we are aware there have been no instances of this reported as yet. We would suggest ensuring that the front of the car and the windscreen are kept clean in order to avoid any sensors or cameras being obscured by dirt, and having the system checked by your dealer if you believe they are faulty.