Abstract: The invention relates to a method for operating a control unit of a motor vehicle during a parked phase. It is the object of the invention to achieve an economical operation during the parked phase and in so doing to perform the service routine. For this purpose, the power supply sets a timer of a clock in the parked phase and then switches itself off. The timer generates a wake-up signal as a function of a current time indication determined by the clock, and a wake-up device of the power supply switches the power supply on again as a function of the wake-up signal. The power supply that has been switched on again then electrically connects the monitoring unit to the on-board network.