Importance

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Abstract

A self-diagnostic apparatus of an air-fuel ratio control system of an internal combustion engine performs processes of starting the diagnostic process as the fuel-cut is started, reading and storing a sensor output at the start of the fuel-cut and counting an elapsed time after the start of the fuel-cut by actuating a timer, reading a time until when the sensor output rises from the start of the fuel-cut from the count value of the timer, calculating a rate of change of the sensor output and comparing the calculated rate of change with an abnormality determining value. When the rate of change is large, the response characteristic of the sensor is normal. When it is small, the response characteristic of the sensor is abnormal (degraded), so that the abnormality of the sensor is stored in a memory and an alarm lamp is lighted to inform a driver of the abnormality of the sensor.

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First Claim