In a method of monitoring a voltage supply of a control unit in a motor vehicle, a supply module which provides the voltages is connected to the components of the control unit via a RESET line and the RESET line is tested every time the control unit is started or all monitoring limits of the supply module show no fault again after the faults of the monitored voltages have been filtered. This test occurs by forced periodic pulses which are generated on the basis of a shift in the limits of the monitoring bands of the supply voltages. The reference voltages VREGUL and VREF are kept independent of each other here in order to prevent system perturbations.