| 摘要 |
PURPOSE:To improve abnormality detecting precision of an exhaust gas concentration sensor, by a method wherein, when a given running state in that the feed of fuel to an engine is to be increased is detected, abnormality of the sensor is detected from an output signal value from the sensor. CONSTITUTION:A control circuit 21 discriminates the running state of an engine 5 by means of detecting signals from a water temperature sensor 16, a number of revolutions sensor 17, and an O2 sensor 19, etc., which are situated to the engine 5, and controls opening and closing of a power valve 12 and an electromagnetic valve 14 according to the discriminated running state. With the power valve 12 opened and an air-fuel ratio of fuel-air mixture extremely enriched, an output voltage from the O2 sensor 19 is increased to a high level. In this case, warming-up of the engine 5 is completed, the O2 sensor 19 is activated, and when an output voltage from the O2 sensor 19 is lower than a given value. during a given time in succession after the power valve 12 is opened, it is decided that the O2 sensor 19 is in an abnormal state.
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