A method to diagnose an exhaust gas sensor (16) disposed in an exhaust gas region (13) of an internal combustion engine (10), whereby a test is made at said sensor to determine whether a change of at least one exhaust gas component, which is detectable by the exhaust gas sensor (16), results in an expected change of the sensor signal (s_Mes), and a device for the implementation of the method are proposed. The diagnosis is only implemented if a specified change in at least one operating parameter (Md, n, agr) of the internal combustion engine (10) and/or at least one parameter (ms_Abg, NOx, ms_NOx) of the exhaust gas in the running operation of the internal combustion engine (10) are detected.The procedural approach allows for a diagnosis without a diagnostic intervention into the operation of the internal combustion engine (10) and without a diagnostic intervention into a metering control system, which if necessary is present and which controls a metering of a reagent substance into the exhaust gas region (13) of the internal combustion engine (10).