Apparatus for diagnosing a circuit arrangement

The invention describes an apparatus for diagnosing a circuit arrangement for a short circuit and/or a line interruption, the circuit arrangement comprising at least two load circuits (10, 20, 30) which are connected in parallel. In the apparatus according to the invention, a current measuring device (40) for providing a current signal (VHS_CUR), which represents the current in the common supply line, is connected in a common supply line to the at least two load circuits (10, 20, 30) which are connected in parallel. Also provided is a voltage measuring device (50) for detecting and providing a node point voltage (V1, V2, V3) of each load circuit in the two switching states of the respective switching element. Finally, an evaluation device (60) is provided, it being possible for the current signal (VHS_CUR) and the node point voltages (V1, V2, V3) to be supplied to said evaluation device, the evaluation device being designed to convert the current signal into at least one logic current value (OC_HS, UC_HS) and to convert the node point voltages into logic voltage values (LS_High, LS_Low) and to infer the type and location of the fault on the basis of prespecified combinations of the at least one logic current value (OC_HS, UC_HS) and the logic voltage values (LS_High, LS_Low).