| 摘要 |
Oxygen sensors (3, 13) are provided upstream and downstream of a three-way catalytic converter (10) in an exhaust passage (9) of an internal combustion engine (1). A controller (2) performs feedback correction of an air-fuel ratio of an air-fuel mixture burnt in the engine (1) by proportional/integral control based on the output of the upstream oxygen sensor (3). In this process, the controller (2) corrects a proportional part by a correction value based on the output of the downstream oxygen sensor (13) (S11, S12). The feedback correction is performed based on a feedback correction coefficient calculated using the proportional part and an integral part. The controller (2) further determines if there is a leak in the exhaust passage (9) based on the correction value (S61) (S62). Higher diagnostic precision is obtained than in the case where the determination is performed based directly on the feedback correction coefficient.
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