Just curious. It must be reading voltage at start-up on the brake circuit. Because you must have your foot on the brake to start the car, that's the circuit they picked. Also, there may not be any other circuits active (depending on what type of connector you have). For example, if your lights are off, there may be no power to read. Once again though, the one circuit they know will be active is the brake light circuit. Have you tried to pull the plug after the car is started to see if the rear PDC stays off? That would be interesting.

y5choi - No it will only use power as long as the car is running and only when your foot is on the brake pedal.