Combustion engines in cars and trucks and their exhaust systems contain many sensors today that capture physical quantities. Sensor signals are forwarded to an engine control unit, which uses this information to control actuators on the engine in such a way that the engine operates optimally. Closely linked to engine control is exhaust gas aftertreatment. The performance of the control units also allows the detection of test cycles and an operation that is changed compared to road traffic. Devices and functions that distinguish between test cycles and road traffic and thus cause different emissions between type approval and operation are called defeat devices and are prohibited.