A method monitors the functional capability of the cooling system of an operating high-voltage accumulator for an electric drive unit of a motor vehicle. The method repeatedly measures the temperature of the high-voltage accumulator by use of a temperature sensor mounted on the high-voltage accumulator; checks whether the measured temperature value is above a cooling threshold temperature; determines a profile of the temperature of the high-voltage accumulator using a temporal sequence of the measured temperature values of the high-voltage accumulator which are above the cooling threshold temperature; and diagnoses that the cooling system is operating correctly if the temperature profile does not exceed a predetermined threshold.