Abstract: A device for testing an electronic control unit with a hardware-in-the-loop simulator to simulate at least one sensor signal and equipped with a two-wire cable via which the sensor signal is outputted, and with a switchover device which is connected to the hardware-in-the-loop simulator via the two-wire cable, so that the sensor signal is receivable from the switchover device. The two-wire cable in the switchover device is routed to a two-pole interface of the switchover device to which the electronic control unit can be connected in order to receive the sensor signal, and the switchover device has two voltage sources, each of which is assigned to a wire of the two-wire cable and can be connected to the respective wire via a controllable switch. In this way, it is possible to continue to supply the sensor with electrical energy via two switchable voltage sources during diagnostics, thus avoiding diagnostic errors.