Patent ID: 8398844

Claim:
Method for diagnosing a NOx readings recorder which acquires a NOx concentration in an exhaust gas tract of an internal combustion engine and comprises two measuring chambers, wherein the exhaust gas to be measured is supplied to the first measuring chamber and an oxygen concentration is set by means of a first oxygen ion pump current, wherein the second measuring chamber is connected to said first measuring chamber and wherein both measuring chambers are disposed in a solid electrolyte, comprising the following steps: the pump voltage at an inner pump electrode in said first measuring chamber and at an oxygen electrode in said second measuring chamber is reduced at a predeterminable operating point such that the oxygen concentration of the exhaust gas appears in the second measuring chamber at a NOx measuring electrode disposed therein; the oxygen concentration in said second measuring chamber ( 120 ) is determined by means of the NOx measuring electrode ( 126 ); said oxygen concentration is additionally determined by means of a separate device; the two oxygen concentration values are compared and a defective sensor is then suggested if the oxygen concentration value determined in the second measuring chamber deviates from the oxygen concentration value determined by means of the separate sensor device by a predeterminable magnitude.