| 摘要 |
<p>PROBLEM TO BE SOLVED: To determine presence or absence of abnormality in detection accuracy to a rich-side air fuel ratio (air fuel ratio at rich side with respect to stoichiometry) of an air fuel ratio sensor at an upstream side of a catalyst.SOLUTION: When a target air fuel ratio is a rich-side air fuel ratio, a rich-side air fuel ratio F/B control is executed to F/B(feedback)-correct a fuel injection amount of a fuel injection valve 21 so that the air fuel ratio of a discharge gas at an upstream side of the catalyst 24 is agreed with the target air fuel ratio (rich-side air fuel ratio) on the basis of an output of an air fuel ratio sensor 25 at the upstream side of the catalyst 24. An air fuel ratio F/B correction value of the rich-side air fuel ratio F/B control is acquired for every target air fuel ratio, and a change characteristic (for example, inclination and the like) of the air fuel ratio F/B correction value to the change of the target air fuel ratio is calculated on the basis of the plurality of acquired data of the air fuel ratio F/B correction value. The sensor failure is diagnosed to determine the presence or absence of abnormality in detection accuracy to the rich-side air fuel ratio of the air-fuel ratio sensor 25 on the basis of the change characteristic of the air fuel ratio F/B correction value.</p> |
