Engine Light Came Back On?

I have an 05 Honda Coupe with a 2.4 manual, but as I was driving it one day the engine light came on. Took it down to the mechanic and they scanned the code and found it was an oxygen sensor. Light when away after replacement. Day later the engine light came back on.

Take it to a better mechanic. Not to be a smart a$$ but seriously. An O2 or oxygen sensor code is usually symptomatic of another problem. An O2 sensors job is to tell the engine control computer whether the engine is operating too rich or too lean and change/control the mixture accordingly. A lot of shops automatically throw an O2 sensor at it because of a code and ignore what is actually causing the engine to be rich/lean such as a vacuum leak, leaking injector, bad EGR valve or any number of other conditions.