METHOD OF DETECTING ABNORMALITY OF AIR-FUEL RATIO SENSOR

摘要

Downstream side air-fuel ratio sensor signal based adaptive air-fuel ratio control. When the air-fuel ratio detected by the downstream side air-fuel ratio sensor is maintained lean unduly, a stuck learning control is performed to decrease a learning value (stbg) to lower the air-fuel ratio. Adaptive learning value update control is performed based on the downstream side air-fuel ratio sensor signal to increase the learning value (stbg) when an upstream air-fuel ratio deviates to the rich side and to decrease the learning value (stbg) when the upstream air-fuel ratio deviates to the lean side. It is judged that the downstream side air-fuel ratio sensor is abnormal (S71) when a certain value or more of decrease of the learning value (S64) and a certain value or more of increase of the learning value (S60) are repeated (S62, S66, S70).