The invention relates to a method for operating a fuel cell system in a mode of reduced power output. The fuel cell system comprises a fuel cell stack (BS) having at least one fuel cell (BZ) with an anode (A), a cathode (K), and a proton exchange membrane, anode and cathode inlets, anode and cathode outlets, and a hydrogen and air supply. In order not to adversely affect the life span of the fuel cell system, the air supply to the cathode (K) is interrupted during the changeover to the mode of reduced power output, and an electric voltage (U) of the fuel cell stack (BS) is reduced by means of a current pulse.