Sensor deterioration judging apparatus and sensor deterioration judging method

Abstract

In a sensor diagnosis process, a controller for controlling an NOx gas sensor performs processing of changing the oxygen partial pressure in a second measurement chamber by changing the oxygen partial pressure in a first measurement chamber (S), processing of detecting a current flowing through a second pump cell before the change of the oxygen partial pressure (S), and processing of detecting a current flowing through the second pump cell after the change of the oxygen partial pressure (S). Furthermore, the controller performs processing of judging whether or not the ratio between the current values detected by the respective current detecting unit falls within an allowable range, judging that the second pump cellis in a normal state if the ratio between the current values falls within the allowable range, and judging that the second pump cellis in a deteriorated state if the ratio between the current values is out of the allowable range (Sand S).