Abstract: A system for detecting a condition of a contactor configured to connect a battery string to a direct-current bus in a vehicle may include a controller configured to open or close the contactor. The system may also include an alternating-current (AC) signal source configured to provide an AC test signal when the controller opens the contactor. The system may further include an AC coupling circuit. The AC coupling circuit may include a primary side of the AC coupling circuit connected to the AC test signal source, and a secondary side connected to the contactor. The system may also include a detection circuit configured to receive an AC return signal corresponding to the AC test signal, and determine a defective condition of the contactor based on the AC return signal.