问：检查引擎灯

Check engine light came went too two different mechanics both said they don’t see anything faulty one of them said it could be small leak somewhere usually gas cap but doesn’t seem that could be it other said maybe changing sensor which was changed the o2 went off now came back on 4 days later not sure what else I can do car is not running different

我的车有51000英里。
我的汽车有自动变速箱。