| 摘要 |
PROBLEM TO BE SOLVED: To accurately diagnose abnormality of an air-fuel ratio sensor and abnormality of an air-fuel ratio feedback control system including control abnormality by an electronic control device comprising a microcomputer or the like, in its turn, attain improvement of control accuracy of the air-fuel ratio feedback control system. SOLUTION: In an exhaust pipe 12 of an internal combustion engine 1, an A/F sensor 26 linearly detecting air-fuel ratio is arranged. In a CPU42 in an ECU41, in accordance with a deviation between air-fuel ratio detected by the A/F sensor 26 and target air-fuel ratio, an air-fuel ratio correction coefficient is set, it is used so as to execute air-fuel ratio feedback control. The CPU42 calculates a deviation between air-fuel ratio detected by the A/F sensor 26 and target air-fuel ratio, also calculates a deviation between the air-fuel ratio correction coefficient and its average value. These calculated abnormality decision elements are made to correspond to a normality/abnormality decision region partitioned by respective each two threshold values, abnormality of an air-fuel ratio feedback control system is diagnosed. |
