| 摘要 |
PURPOSE:To enable fuel consumption of an engine and its drivability to be prevented from worsening, by considering an air-fuel ratio sensor to be abnormal due to its deterioration and stopping a feedback control of air-fuel ratio if a difference between the maximum level and the minimum level of an output of the air-fuel ratio sensor is less than a predetermined value. CONSTITUTION:An air-fuel ratio sensor, provided in the upstream of a catalytic converter, detects concentration (O2) of a specific component in exhaust gas, and a control device detects a level difference, between the maximum level of the output and its minimum level, for a predetermined period by a level difference detecting means to be compared with a predetermined value by a comparing means. As the result, when the level difference is in the predetermined value or more, an air-fuel ratio regulating means performs a feedback control of air-fuel ratio accordance with an output of the air-fuel ratio sensor. While if the level difference is less than the predetermined value, the air-fuel ratio regulating means stops the feedback control of air-fuel ratio by considering the air-fuel ratio sensor to be abnormal due to its deterioration. In this way, fuel consumption, drivability, exhaust emission, etc. can be prevented from worsening due to an overrich or overlean state.
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