well, i have my second 02 sensor hooked up electronically, but its on the pipe within 2 non foulers, not like its reading right anyway. all it does is show cat effienciency

 

I disagree... if the CEL goes on, then turns off there IS a problem that is intermittent (like a failing O2 sensor). The sensor may be within the ECU's tolerances, but on occasion it may fall below them as the sensor switches between lean and rich more slowly.

 

Mileage is 90k. I'll look at my records to see which O2 was replaced and which one the code is indicating.

My mechanic said not to worry about it since the CEL turned off, but it seemed to me that it wouldn't have come on if there wasn't a problem in the first place. Could a change in fuel have affected it? Like I said, as soon as I bought the car I filled it with Chevron Plus and the CEL turned off within 20 miles.

 

I doubt the fuel change would do it unless it was too low in spec, as for it not having a problem I still say this because there are two stages of problems 1/. is a soft error code which is stored and no CEL will come on but its a warning that it could cause a problem later if it happens again, 2/. the CEL is on indicating a problem