| 摘要 |
PROBLEM TO BE SOLVED: To improve the frequency of LAF sensor deterioration determination when conducting air-fuel ratio control while monitoring the deterioration of an LAF sensor. SOLUTION: If prescribed monitor condition failure occurs in the course of deterioration determination of the LAF sensor as shown in (a) and (b), an LAF prohibition timer is operated as shown in (c) to prohibit lean burning from occurring for prescribed time (for example, 7 seconds). If monitor conditions are satisfied again within the prescribed time, prohibition of lean burning is continued. Upon the completion of LAF sensor deterioration determination, lean burning is permitted after prescribed time (for example, two seconds) shorter than the above prescribed time as shown in (c) and (d) passes. As a result, if monitor condition failure occurs in the course of monitoring, lean burning is prohibited. It is thus possible to prevent generation of immediate shift to the lean burning as found in a conventional way, thereby improving the frequency of the LAF sensor deterioration determination.
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