A method for determining the total leak rate of a system impinged upon by pressure and connected to a control apparatus comprising a valve battery with a test side and a reference side, the valve battery being controllable via a measuring unit, encompasses the following steps: filling the system and the control apparatus with a test medium; closing the connection between the system and the control apparatus; opening a reference leak is on the valve battery; determining the reference leak rate; opening the connection between the system and the control apparatus; and determining the influence of the system on the reference leak rate. A control apparatus comprises a valve battery that is controlled by a measuring unit and is provided with a test side and a reference side which are separated with the aid of a differential pressure sensor and a test and check valve which is connected thereto.