Check engine light on, possibly related to ECO button

The check engine light is not related to something you did "a few days ago". That is as likely as running out of gas because you hit a pot hole last week.

The second problem has to do with the diagnostic fault code. We need the exact code number because there's a dozen codes related to every sensor, and they mean very different things. Also, the code did not say to replace the knock sensor. Fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is actually the cause of that code only about half of the time. First we have to rule out wiring and connector terminal problems, and mechanical problems associated with that part.