Abstract: The invention provides a fault tolerant output stage for a digital two-conductor bus data communication system of the type having a transmission module and a reception stage which contains a bus signal intermediate processing module and a reception module connected downstream that conditions incoming bus signals for a data processing unit which is connected downstream. A state detection module is connected to the bus lines to detect a short-circuit between the bus lines, in which case the transmission module can be switched over between a difference mode of operation and a single-wire mode of operation under the control of the state detection module.