cel after replacing o2 sensor? why?
 

ok, so my cel came on, went to autozone and got the obii diagnostic tool, said my rear bank was out, so went to gadget's site and got a replacement, changed it, pulled the fuse, waited a bit. cel off. great. now half a tank later, still ÅÅÅÅty gas mileage and the cel comes back on. i'm going to autozone to obii it again, but any suggestions? i think i did it right, jesus. thanks, dd

This is why it is hard to diagnos problems with CEL codes. Just because it gives an O2 code doesn't mean that O2 sensor is bad. You can get a bad O2 code from a dirty or malfunctioning MAF too. (although this is usually the upstream sensor not downstream). The downstream sensor usually measures catalyst efficiency. You may have a bad converter, a bad MAF, bad upstream O2 sensor, or stuck injector. Bad gas can do this too.

I would start by getting the new CEL code as well as cleaning the MAF.