Method for Operating a Braking Device and Braking Device for Motor Vehicles

A method operates a braking device for motor vehicles, in particular for utility vehicles. Along a trailer supply line for supplying air to a parking brake of a trailer and/or a trailer control line for supplying air to an operating brake of a trailer, the air pressure is measured by at least one pressure transducer and is transmitted in the form of an electric signal to an electronic control unit of the motor vehicle. In the event of a faulty pressure change response, an open trailer supply line and/or an open trailer control line is detected.