The invention relates to a device for operating a voltage converter (1), in particular a DC converter, of a motor vehicle, which voltage converter has at least two parallel-connected converter strands (4, 5) which are connected between a high-voltage side (2) and a low voltage side (3) of the voltage converter (1) for converting the voltage, having at least one cooling device (8) carrying a coolant (9) and assigned to the converter strands (4, 5), wherein each of the converter strands (4, 5) is assigned at least one temperature sensor (6, 7), comprising the following steps: a) detecting an input voltage, an output voltage and an operating current of each converter strand (4, 5), b) detecting a current converter strand temperature by means of the respective temperature sensor (6, 7), c) determining a respective coolant temperature as a function of the values detected in steps a) and b), d) comparing the two determined coolant temperatures (T_1, T_2) with each other and e) determining the serviceability of the temperature sensors (6, 7) on the basis of the result of the comparison.