A method checks a sealing of an interior space of a plug connection that is to be tested. The plug connection has two plug connection elements, namely a plug connector element and a mating connector element, the plug connector element being plugged into the mating connector element in a plug-in direction. One of the plug connection elements additionally has a test opening to the interior space, via which, for the purpose of checking the sealing, a test medium is applied to the interior space, and the test opening is then sealed toward the interior space.