Method to test for a leak in a fuel tank system

A method to test for a leak in a fuel tank system of a motor vehicle includes a fuel tank is cut off during the overrun by means of at least one cutoff device, and the pressure, which builds up in the fuel tank within a specifiable time interval is acquired; if a specifiable maximum pressure or a specifiable vacuum threshold is not achieved, said cutoff device is opened and closed again after a specifiable time period, and a vacuum is produced and acquired in a subsequent vacuum phase, and a parameter, which characterizes the leak tightness, is determined and evaluated from the vacuum achieved within a specifiable time period and the overpressure, which is achieved, and the test for a leak is concluded; if the specifiable maximum pressure is achieved, a parameter characterizing the leak tightness is determined from the acquired overpressure and the specifiable overpressure threshold and is compared with a specifiable reference value and for the case that the determined parameter is smaller than the reference value, a leak-proof fuel tank system is suggested and the test for a leak is concluded, and if the determined parameter is greater than the specifiable reference value, the cutoff device is opened and a vacuum is produced and acquired in the fuel tank in a subsequent vacuum phase, whereby a leak-proof fuel tank system is then suggested if a specifiable vacuum threshold is achieved, and hence the test for a leak is concluded, and whereby the test for a leak is then concluded if the vacuum threshold is not achieved within a specifiable time period, and hence the parameter characterizing the leak tightness is evaluated.