One problem related to brake light switch has been reported for the 2003 BMW 3 Series. The most recently reported issues are listed below.
Brake lights on both sides gets stuck on once the pedal is pressed. This produces no error codes. I was told it could be the brake pedal pressure sensor switch. I changed this and it did nothing. This is very dangerous to other drivers because they are not sure if the car is braking as the light is always on and will burn out the bulbs and melt the housing if constantly on. This can be reproduced either while parked or in motion.