| 摘要 |
PURPOSE:To accurately diagnose the deterioration of an oxygen sensor by detecting that the oxygen sensor does not follow immediately when the output of the oxygen sensor is changed over from a rich side to a lean side. CONSTITUTION:When an engine 1 is in a predetermined rich air/fuel ratio operating state and fuel is cut, the response time required until the output of an oxygen sensor 11 crosses the slice level corresponding to an objective value from a rich side to change to a lean side is measured and a diagnosis reference value diagnosing the deterioration of the oxygen sensor 11 is set on the basis of the number of rotations of the engine 1. Thereafter, the response time is compared with the diagnosis reference value to diagnose the deterioration of the oxygen sensor 11. In this case, by detecting that the oxygen sensor 11 does not follow immediately when the output thereof is changed to the rich side, it is cleared that contaminant is present and the deterioration of the oxygen sensor 11 is diagnosed. Therefore, the deterioration of the oxygen sensor can be accurately diagnosed. |
