the measure has been carried out a defect of the pressure switch is identified the method according to various embodiments permits reliable testing of whether the pressure switch is clamping in the low pressure position identification of such a defect of the pressure switch means that incorrect diagnoses of the tank ventilation system can be prevented and the reliability of the testing of the function of the tank ventilation system improved overall the method can be carried out both when the internal combustion engine is at a standstill and when it is in operation so testing of the function of the pressure switch can be carried out with great frequency according to an embodiment of the method the measure for increasing the pressure in the tank ventilation system above the pressure limit consists in actuating when the internal combustion engine is at a standstill a tank ventilation valve of the tank ventilation system which valve is arranged in a connecting line between a fuel vapor accumulator of the tank ventilation system and an intake pipe of the internal combustion engine such that the tank ventilation system is pneumatically connected to the intake pipe this embodiment of the method allows testing of the function of the pressure.