A method and an apparatus for controlling a braking system of a vehicle. The braking action is established or regulated at at least one wheel brake, by electrical structure, as a function of a driver's braking input. A capability for conventional action by the driver is cut off by a valve. A pressure medium is enclosed in a portion of the braking system. In at least one operating state in which an expansion in the volume of the enclosed medium may be expected, the valve is briefly opened in order to reduce the expansion in volume.