The invention relates to a method for detecting selection of a pump assembly (25, 32), for instance a fuel pump assembly, in which at least two pump assemblies are provided. By means of a control unit (12), the lambda signal is scanned continuously by means of lambda probes (21). As a function of the lambda signal ascertained, the maximum fuel injection quantity is limited to the supply quantity of a fuel pump assembly (25, 32), and simultaneously a limitation of the air quantity to the air quantity corresponding to the maximum fuel injection quantity is effected. The limitation of the maximum fuel injection quantity and of the associated air quantity is effected via a throttle valve element (13.1), which is triggered by the control unit (12).