A procedure for checking the functionality of a tank ventilation valve of a tank ventilation system for a motor vehicle with a fuel tank, an adsorbing filter, which is connected to the fuel tank over a filter line and which provides a vent pipe, and with the tank ventilation valve, which is connected to the inlet manifold of a combustion engine that provides an actuator for the idle mode over valve pipes, is thereby characterized, in that the mass flow that flows through the tank ventilation valve in the idle mode of the combustion engine and the mass flow that flows through the actuator for the idle mode are detected and in that the functionality of the tank ventilation valve is deduced from a variation of the actuator for the idle mode.