| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to detect abnormality in a constant-current circuit for changing the output characteristic of an oxygen sensor, and to shorten the time required for diagnosing abnormality.SOLUTION: A constant-current circuit 27 is controlled so as to stop a constant current Ics (i.e., Ics=0) flowed between sensor electrodes 33, 34 of an oxygen sensor 21, before activation of the oxygen sensor 21, during engine fuel-cutting, and after engine stop. By focusing on that, when abnormality (e.g., a fault) occurs in the constant-current circuit 27, the output of the oxygen sensor 21 while the constant-current circuit 27 is controlled so as to stop the constant current Ics becomes different from its output during normal time, abnormality diagnosis is performed in which the presence of abnormality in the constant-current circuit 27 is determined depending on whether the output of the oxygen sensor 21 before activation of the oxygen sensor 21, during engine fuel cutting, and after the engine stop (i.e., the constant-current circuit 27 is controlled so as to stop the constant current Ics) has exceeded a prescribed normal range. |
