O2 sensor questions

[Mixednuts]

Hello all! I'm new to the forums and have hopefully easy questions.
I have a check engine light on and the code is for O2 sensor. Bank 1 sensor 1. Is this the sensor before the cat or after?
The nuts on the sensor studs are so rusted the flats and points are no longer there. Any suggestions on removing these? I was going to get my Dremel tool out with a cut off wheel and work at the nuts to split them and run them off that way. Any eaiser suggestion would be appreciated.
Thanks in advance,
Pete

[Spork]

Code P0420 is usually after the cat if that is what your code was.

The O2 sensor is made like a spark plug it screws into the exhaust pipe. I'd try a wire brush and some penetrating oil first.

[thepinktaco]

Code P0420 is usually after the cat if that is what your code was.

The O2 sensor is made like a spark plug it screws into the exhaust pipe. I'd try a wire brush and some penetrating oil first.

Um, No and no.

The Bank 1 Sensor 1 before the cat sensor 2 after. The bank is the side that number 1 cyl is on. P0420 can be caused by a bunch of things. Check for an exhaust leak right by the sensor where the downpipe and cat bolt together. I couldnt keep gaskets in there so I welded it together.

And the O2 is held in by 2 nuts like he said. Try getting vise grips on them to see if you cant get them to move if not cut the nut off. Dont cut the stud off though or you will be screwed.

[Mixednuts]

That's what I thought. No leaks in the system. 190,000 miles on the original stuff. It's due.
Looks like I'll be cutting off the nuts. Thanks for the help guys

[98taco4x]

You also get a bank 1 code if the MAF is dirty so you may want to try and clean it first since it would be the easist thing to do and see if that gets rid of it.

[SWAINBUILT]

Use a Turbo socket to get those nuts off. If the nut can be removed they will do it!

[Pietro]

you'd be amazed at how rusty those nuts can get while still coming off just fine

get some good penetraiting oil on it before turning them