Method and device for operating a circuit arrangement, circuit arrangement

The invention relates to a method for operating an electric circuit arrangement (1) which has a low-voltage sub-network (2) and a high-voltage sub-network (3). A test signal is transmitted from one of the sub-networks (2, 3) to the other sub-network (3, 2) in order to detect a fault depending on the reception of the signal in the other sub-network (3, 2) and to switch the circuit arrangement (1) to a safe state. A data bus (5), which connects a low-voltage control unit (6) of the low-voltage sub-network (2) to a high-voltage control unit (7) of the high-voltage sub-network (3), is operated with a maximum bus load at least temporarily as a test signal so that data packets are transmitted at fixed time intervals, and a fault is detected depending on a delay of the last received data packet, said delay being detected by the control unit (7, 6) receiving the data packets.