fig3 shows a diagram with diagnostic values diag the method starts at a step s 1 a step s 2 can be provided for testing whether at least one predefined diagnostic condition b applies the at least one predefined diagnostic condition b can comprise in particular a predefined operating state of the internal combustion engine for example overrun conditions or generally an operating state with an essentially nonvariable load and as a result an essentially nonvariable and predefined oxygen concentration in the exhaust gas the at least one predefined diagnostic condition can also comprise in particular a small nox measured value of the exhaust gas sensor sens which is below a predefined nox threshold value the predefined nox threshold value can for example be approximately 50 parts per million however the predefined nox threshold value can likewise be higher or lower than 50 parts per million it is also possible for further or other diagnostic conditions b to be provided preferably the predefined operational state lasts for the duration of the diagnostics performed on the exhaust gas sensor sens the duration is for example approximately five seconds but can also be longer or shorter a step s 3 can be provided in which the further pump current ipo is sensed the further pump current ipo is dependent on the oxygen concentration in the first chamber mk 1 and is preferably representative of the oxygen concentration in the first chamber mk 1 the further pump current ipo is preferably sensed at the start of the diagnostics the further pump current ip 0 can in particular also represent an oxygen concentration.