| 摘要 |
PURPOSE: To provide a device for diagnosing deterioration of air-fuel ratio sensor which is constituted to execute preliminary diagnoses during the feedback control of air-fuel ratio and perform deterioration diagnoses associated with forcible variation in accordance with the results of the preliminary diagnoses. CONSTITUTION: An ECU(engine control unit) 40 judges whether or not the number of inverting times of an O2 sensor 14 exceeds a prescribed value based on the output voltage of the sensor 14 which the sensor is under the feedback control of air-fuel ratio and, when the judgment result is 'Yes', the unit 40 judges that the sensor 14 is normal and does not diagnose the deterioration of the sensor 14. When the result is 'No', the ECU 40 forcibly excites the air-fuel ratio between the 'Rich' and 'Lean' after initializing the air-fuel ratio and judges whether or not the output voltage of the sensor 14 exceeds a reference value for diagnosis within a prescribed period of time. When the judgment result is 'Yes', the ECU 40 judges that the sensor 14 is normal and, when the result is 'No', the ECU 40 judges that the sensor 14 has deteriorated and calls upon the driver of its own vehicle to exchange the sensor 14 by turning on a warning lamp 41. |
