When a brake pedal position sensor fails, it can cause the brakes to stop working properly. This can lead to serious accidents if the vehicle is not able to stop in time. The brake pedal position sensor is responsible for sending a signal to the electronic control unit (ECU) when the brake pedal is depressed. If this signal is not received, the ECU will not activate the brakes. In some cases, the brake light on the dash may also come on as a warning to the driver that there is a problem with the braking system.