Modular hydraulic brake system for a rail vehicle, wherein the rail vehicle comprises a transmission medium for transmitting to a vehicle electronic system having a brake controller or a vehicle controller and a power supply line to a power supply source, the brake system comprising the following: at least one function module (100, 101), which can be coupled to an actuator and/or a sensor (302, 303) and has a control unit and a module communication interface designed to provide at least one of the following functions: - to make available control signals for the actuator and/or to acquire sensor data, - to identify unambiguously the at least one function module (100, 101) and/or the actuator and/or the sensor, - to assign functions to the at least one function module (100, 101) and/or to the actuator and/or to the sensor or to change said functions, - to determine loading of a function module (100, 101) and/or of an additional module and/or of the actuator and/or of the sensor and to make available a result; a further function module (102, 103), which can be coupled to the function module; characterised by a universal interface for transmitting control data, via a signal channel, on the transmission medium between the at least one function module (100, 101) and the vehicle electronics system, wherein the universal interface is designed to selectively transfer control data for the function module and the further function module (102, 103), wherein each function module within the system can be individually identified via the universal interface and an identification or addresses assigned to each function module and each additional function module is/are awarded for this purpose and an unambiguous identification is permitted, and wherein the universal interface makes available a power supply connection for the at least one function module (100, 101, 102, 103) independent of control data, wherein the at least one function module (100, 101, 102,...) can be coupled to an additional module making available a predetermined function, and wherein the universal interface is designed to interrogate information about the at least one function module (100, 101, 102,...) and/or the additional module and to make it available to the vehicle electronics system, in order to permit a determination of a configuration, and wherein the at least one function module (100, 101, 102,...) and/or the additional module is/are designed to log in and out at the universal interface. at least one function module (100, 101), which can be coupled to an actuator and/or a sensor (302, 303) and has a control unit and a module communication interface designed to provide at least one of the following functions: - to make available control signals for the actuator and/or to acquire sensor data, - to identify unambiguously the at least one function module (100, 101) and/or the actuator and/or the sensor, - to assign functions to the at least one function module (100, 101) and/or to the actuator and/or to the sensor or to change said functions, - to determine loading of a function module (100, 101) and/or of an additional module and/or of the actuator and/or of the sensor and to make available a result; - to make available control signals for the actuator and/or to acquire sensor data, - to identify unambiguously the at least one function module (100, 101) and/or the actuator and/or the sensor, - to assign functions to the at least one function module (100, 101) and/or to the actuator and/or to the sensor or to change said functions, - to determine loading of a function module (100, 101) and/or of an additional module and/or of the actuator and/or of the sensor and to make available a result; a further function module (102, 103), which can be coupled to the function module; characterised by a universal interface for transmitting control data, via a signal channel, on the transmission medium between the at least one function module (100, 101) and the vehicle electronics system, wherein the universal interface is designed to selectively transfer control data for the function module and the further function module (102, 103), wherein each function module within the system can be individually identified via the universal interface and an identification or addresses assigned to each function module and each additional function module is/are awarded for this purpose and an unambiguous identification is permitted, and wherein the universal interface makes available a power supply connection for the at least one function module (100, 101, 102, 103) independent of control data, wherein the at least one function module (100, 101, 102,...) can be coupled to an additional module making available a predetermined function, and wherein the universal interface is designed to interrogate information about the at least one function module (100, 101, 102,...) and/or the additional module and to make it available to the vehicle electronics system, in order to permit a determination of a configuration, and wherein the at least one function module (100, 101, 102,...) and/or the additional module is/are designed to log in and out at the universal interface.