A device for monitoring a voltage supply for a vehicle system includes a self-diagnostic function which evaluates a logic state of the comparison signal which is output by a comparison device as a function of an input signal, and checks whether a reset signal which corresponds to the output comparison signal is generatable. The self-diagnostic function recognizes a malfunction of the comparison device when the evaluated logic state of the comparison signal does not match an expected logic state. The self-diagnostic function recognizes a malfunction of the reset device when the checked logic state of the reset signal does not match an expected logic state.