The manual says to drive carefully and consult a BMW dealer as soon as possible. It seems like a failure of ADB/ASC-T braking system. I want to know the cause and what it might entail to fix this before I go to the dealer.
I've had this happen on a chevy with just the Brake light. A sensor in the combination valve might have set off the warning lamp. Sometimes after brake work, the lines are off balance and the car computer thinks you have lost pressure in one of your brake systems. Sometimes its a matter of stepping on the brake, starting the car, and then release and re-apply the brake pedal. Doing so releases any pressure, and then resets the metering pin in the system. Any manual is going to tell you to consult the dealer if a light goes on. Ask a local tech at the dealer what might have set it off.
