Cel :(

[Cc000]

So recently a friend decided it'd be funny to put diesel in my corolla.
I got the engine flushed (paid about $600) and the car had been running smoothly ever since.
2 weeks ago my CEL came on. I went to have it checked and it was a p0420 code. However, the light goes on and off randomly, sometimes it'll stay on for a couple days then go off then come back on again.
I haven't noticed any decreased gas milage or rough idling or weird smells, etc. so could it just possibly be a faulty o2 sensor? I really hope it is.

Thanks!

 

[Donabed Kopoian]

What specifically is the code?

 

[06CorollaXRS]

If you have a P0420 code and no other current or pending codes, the problem is almost always the converter. Putting an O2 sensor in is most likely a waste of money if there are no other symptoms.