LOVE my Xterra!! 04 SE V6 (non-supercharger) with 138,000 on her. I just had my knock sensor replaced (I live in a county that requires emissions testing) as well as my driver-side catalytic converter. They tried to clean the O2 sensor but the CEL has come back on both times, so I have to get it replaced. It seems that I'm getting charged 2 arms and one and a half legs to have it replaced. Luckily, they received the wrong sensor while I was doing research so I have to reschedule. I'd love to replace this myself because it seems MUCH cheaper and much easier. I need to get this done so I can reset my CEL and get my emissions test so I can renew my tags. Can anyone give me some insight and help on replacing the O2 sensor?? I'm thinking I will go try to find a repair guide tomorrow help me with this.

which one needs to be changed, you have 4 of them. Two are really easy to get to, the other two not so much. I had to drop my passenger side down tube to get it out. That involved removing the tranny cross member to get it out.

The code that is showing is P0174 (Bank 2 System Too, Lean). Does that help you in helping me?

From what I'm understanding now is that it's the upper left, which is easy to replace because it's a screw-down??