Abstract: Disclosed is a process for operating a brake actuation unit of a motor vehicle brake system of the ‘brake-by-wire’ type. The brake system has a brake booster, a master brake cylinder, and a pedal travel which interacts with the brake pedal and due to a resetting force acting on the brake pedal can be simulated in the ‘brake-by-wire’ operating mode independently of an actuation of the brake booster, and which can be enabled in the ‘brake-by-wire’ operating mode when the force-transmitting connection between the brake pedal and the brake booster is decoupled and can be disabled outside the ‘brake-by-wire’ operating mode.

Abstract: The present invention discloses an electronically controllable brake actuating system for automotive vehicles, including an unpressurized pressure fluid supply reservoir, a pressure source actuatable by an electronic control unit, the pressure of which can be applied to wheel brakes of the vehicle, further including a device for detecting the driver's wish for deceleration as well as valve assemblies inserted upstream of the wheel brakes and connecting the wheel brakes alternatively to the pressure source or the pressure fluid supply reservoir. In order to increase the operational or functional reliability of a system of this type, the present invention discloses the provision of means for detecting gases or air disposed in the system.