NOVELTY - The method comprises switching a fuel cell system (4) to a temporary stop mode during requirement and then again restarting from the stop mode, supplying a fuel cell (7) of the fuel cell system with an air mass flow via an air conveyance device (11) on the cathode side and with a combustion gas mass flow via a fuel gas supply device on the anode side, and carrying out a requirement for changing to the stop mode in certain driving situations based on the vehicle and then verifying it whether the operating conditions of the fuel cell system allow for a change to the stop mode.    USE - Method for operating a fuel cell system in a vehicle.    ADVANTAGE - The method is capable effectively, easily, efficiently and comfortably operating the fuel cell system with less energy consumption, high functionality and long service life, reduces the emission of pollutants, prevents rapid aging of the fuel cell, and reduces the risk of corrosion.    DETAILED DESCRIPTION - The method comprises switching a fuel cell system (4) to a temporary stop mode during requirement and then again restarting from the stop mode, supplying a fuel cell (7) of the fuel cell system with an air mass flow via an air conveyance device (11) on the cathode side and with a combustion gas mass flow via a fuel gas supply device on the anode side, and carrying out a requirement for changing to the stop mode in certain driving situations based on the vehicle and then verifying it whether the operating conditions of the fuel cell system allow for a change to the stop mode. If the change is allowed, the switch to the stop mode is then carried out. In the case of a restart of the fuel cell system required based on the vehicle, the settings of the stop mode are overridden. The switch to the stop mode comprises that the air mass flow conveyed by the air conveyance device is deactivated in the case of continuing electrical contacting of the fuel cell or reduced to a specified value, where the pressure of the supplied combustion gas is reduced to a specified value. The unconsumed fuel gas is fed back into the fuel cell system from an area towards the anode via a recirculation conveying device together with fresh fuel gas from a valve device for fuel gas supply to the anode. The recirculation conveying device is formed as electro-motorically driven blower. The change to the stop mode comprises that the mass flow conveyed from the recirculation conveying device to a predetermined value. The recirculation conveying device runs during the stop mode to predetermined low number of revolutions. The pressure of the fuel gases is regulated to a predetermined value range. The fuel cell is electrically coupled with an electronic unit for receiving the power of the fuel cell, where the excess power of the fuel cell is stored in an energy storing device by the electronic unit. An electric current from the fuel cell is drawn by the electronic unit after the change to the stop mode until a determined voltage is reached after which the fuel cell is regulatably kept at a constant voltage. The air conveyance device is kept during the change to the stop mode. After the stop mode has a predetermined time period, a temporary increase of the air mass flow is carried out where after reaching the predetermined value of air mass flow is switched back into the stop mode. The time period is given in the order of magnitude of 7-15 minutes. A flow compressor is used as air conveyance device, runs during the stop mode to predetermined low number of revolutions, and is an electric turbocharger. The given predetermined low number of revolutions is less than 12000 U/minutes. A flow connection is opened between the air mass flow for fuel cell after the air conveyance device and an exhaust gas flow from the fuel cell during the change to the stop mode. A line provided with a valve for discontinuous reduction of water guides from the area of the anode circulation and/or gas guides from the area of the anode circulation into the area of the air mass flow flowing to the fuel cell, where the valve is closed during the stop mode. The fuel cell is formed as proton exchange membrane fuel cell and is driven with hydrogen as fuel gas.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of a fuel cell system.    Fuel cell system (4)    Fuel cell (7)    Cathode chamber (8)    Air conveyance device (11)    Supply line. (12)