| 摘要 |
PROBLEM TO BE SOLVED: To improve the output characteristic of a gas sensor and yet increase the accuracy of abnormality diagnosis.SOLUTION: An O2 sensor 17 has a sensor element 31 composed by using a solid electrolyte 32 and a pair of electrodes 33, 34 provided at positions sandwiching the solid electrolyte 32, and outputs an electromotive force signal corresponding to the air-fuel ratio of engine exhaust, the exhaust being an object to be detected. A constant-current circuit 43 is connected to the sensor element 31. A microcontroller 41 executes abnormality diagnosis pertaining to the output responsiveness of the sensor element 31 on the basis of a change mode of electromotive force output at the time when the electromotive force output of the sensor element 31 changes. When executing abnormality diagnosis, the microcontroller 41 executes limiting of constant-current supply by the constant-current circuit 43 before actually executing the abnormality diagnosis. |
