| abstract |
An abnormality diagnosis system for a limiting current gas sensor for detecting oxygen-containing gas contained in exhaust gas of an internal combustion engine is provided. In a gas sensor, a decomposition current value of water (H 2 O) is detected and based on deviations S540 and S550 from a reference decomposition current value S535 of water corresponding to the concentration of water contained in the exhaust gas S530, Diagnose whether there is an abnormality in the output characteristics of the limiting current gas sensor S545, S555. As a result, not only abnormalities in output characteristics but also minute abnormalities can be diagnosed accurately and easily. The reference decomposition current value of water can be obtained based on the concentration of water detected by a separate humidity sensor or the decomposition current value of oxygen detected by the limiting current gas sensor. In the latter case, the obtained reference decomposition current value of water may be corrected based on the oxygen decomposition current value detected at the time of fuel cut. [Selection] Figure 5 |