A method for testing the operability of a tank ventilation system and tank ventilation systems in motor vehicles

Method for testing the operability of a tank ventilation system of a vehicle, comprising a tank (10), an adsorption filter (20) connected to the tank (10) via a connecting line (12) is connected and by a selector / shut-off means (70) closeable has ventilation line (22), a tank vent valve (90) which is connected to the adsorption filter (20) via a valve line (24), in which by means of a controllable pressure source (50) an excess pressure relative to the atmospheric pressure introduced into the tank ventilation system and to determine the pressure curve detects at least one operating characteristic variable of the pressure source (50) during the introduction of the positive pressure and from this deduce the presence of a leak is (tightness), characterized in that the excess pressure by opening the tank venting valve (90) and simultaneously closing the switching / shut-off means (70 ) is reduced.