O2 sensor replacement

I was getting poor milage so I had the front o2 sensor changed. The milage was great for a few months. It was around 29 mpg hw. Now it's down to the low 20's again. What can be done to bring it back to 28-29 mpg.

Thanks for answering my question. No engine light on. I had the sensor done at a local shop. I can see the o2 sensor under the car after the catalytic converter. Where's the other one located? Is it under the hood somewhere and what should I look for that can cause this problem?
Thanks again

Visually checked sensor wires and everything looks ok. What next?

Hello, I have a 2004 pontiac grand prix. The check engine light is on because of the bank 1 oxygen sensor. So I replaced it and reset the light. Well the light came back on and so I tested it again and the message said that the oxygen sensor is defective. So I took the part back and got it replaced. I reset the light again and it came back on, with the same message. I talked to a mechanic and he told me that I have to drive the car so it can register. Its been 3 weeks and the light is still on. Can u help me?

I am getting code P0141 from my car which is apparently the Oxygen Sensor (from what I read on the net). From what I read it looks like it is Bank 1, Sensor 2.I think this means that it is the O2 sensor after/behind the catalytic convertor. Can anyone confirm this?

My husband does not seem to think we should replace this as it is costly and the car runs pretty good (except on the highway, where it "surges" and hesitates intermittently). I disagree because we have a small child and I do not want to risk being stranded alongside the highway or doing further damage to the vehicle. Does anyone know how "important" it is to fix the O2 sensor?

Before I go ahead and replace this part is there anything else we should check (i.E. Fuse.I would have no idea which fuse it is)

THANK YOU for any help you can give :)

I am trying to change out the o2 sensor downstream and cannot get the old sensor undone. How do I fix this? Which way do I turn it to get it to un do?

How do I find and replace the oxygen sensor in my 97 grand prix

Where is(are) the oxygen sensor(s) located? Is it(they) hard to replace?

Should be past the exaust manifold on the pipe going toward the catyalitic converter, either before or after the converter.