treatment installation in which the method according to the invention is employed fig1 illustrates only the components that are required in order to gain an understanding of the invention in particular the fuel cycle has not been illustrated the air required for combustion is fed to the internal combustion engine 10 via an induction duct 11 as seen in the direction of flow of induction air a load sensor in the form of an air mass flow meter 12 a throttle valve block 13 with a throttle valve 14 and a set of injection valves 15 the number of injection valves 15 is equal to the number of cylinders although only one of the valves 15 is shown and are disposed in succession in the induction duct 11 however the method according to the invention can also be used in a system which has only one injection valve for all the cylinders central injection system single point injection system or in which fuel is injected directly into the respective cylinders direct injection high pressure injection on an outlet side the internal combustion engine 10 is connected to an exhaust pipe 16 in which a three way exhaust catalytic converter 17 is disposed the simplified term exhaust catalytic converter is used below to indicate the three way exhaust catalytic converter 17 a sensor configuration for the exhaust gas after treatment includes inter alia an oxygen measuring pick up in the form of a lambda sensor 18 which is disposed upstream of the exhaust catalytic converter 17 and an nox sensor 19 for determining a nox concentration and for supplying a corresponding signal to a trim control downstream of the exhaust catalytic converter 17 the oxygen measuring pick up 18 used may be either a broadband lambda sensor which emits.