Method and apparatus for operating a NOx-sensor located in the exhaust line of an internal combustion engine

The method involves coordinating measurement values of a nitrogen oxides (NOx) sensor in an exhaust system with earlier signals values for the same NOx content. This involves setting a defined engine operating state, detecting at least one NOx sensor value, comparing this with values for the known NOx content, determining the difference, determining a correction value and correcting the measured value with the correction value. An Independent claim is included for an arrangement for determining the nitrogen oxides content in the exhaust gas system of an internal combustion engine.