rear oxygen sensor-2000 1.8tq
 

I've got a cel for the rear o2 sensor and the car has 103k miles on it, so I figured I'd go ahead and replace it. I can't stand that pesky check engine light! Can anybody tell me how they have gotten the rear oxygen sensor out? I can put my hand on it, put a o2 sensor socket on it, but there's no room to work. I put a universal joint and a long extension on it, and the rachet has room to work under the coolant recovery tank. But then there's so much flex in the tool that I can't break it loose. The stupid thing can't be this difficult! So, I figured I'd ask the forum community, cause I know somebody out there has probably done this recently. And yes I searched but didn't find much help. Thanks for any suggestions.

Hmm, I know when a buddy and I ripped the cat out a few months ago, the rear O2 was a PITA, but not that bad. I'm trying to remember if we had already removed the bolts to the cat and moved it into a better position to get the O2 sensor out. I know it would be an unpratical amount of extra work though, so I'm not quite sure what to tell you. Maybe if you very carefully try to use an open end wrench on it, you might be able to get it loose. Still not very much room to work though. Good luck.

What style of O2 socket did you use? The one that's just like a deep socket with a slit or the one that's an open socket with a slit and a piece that goes off to the side for the ratchet to connect to? I highly recommend the latter over the former.

Also, soak that thing good with Kroil (preferred) or PB Blaster (still decent) and you can use a torch on it if you have one.

I haven't done rears on an A4 so if you can't get it with my preferred style of O2 sensor then you might be able to get it with an offset box wrench or something. You can cut the elecrical cord to it to slip the wrench on.

i had to replace mine a couple months ago. its alot of work the way i did it but you can get an open end stubby wrench on it and it should come loose pretty easy, ive got 140k on mine and they turned out easy. i had the cat unbolted from the turbo and it gave me a little more room but i bolted it back on b4 i put the o2 sensor in so i had to thread it in and tighten it down so it can be done.

Got it!
 

Thanks guys, I got it off. I cut the wires off at the sensor and put a 1/2 inch drive deep socket on it. Then a u joint and a long extension across the top of the transmission bell housing. With the coolant recovery tank swung out of the way, there's enough room to work a ratchet. The o2 sensor socket I have is 3/8 drive and that just wouldn't cut it. With the 1/2 inch drive socket, it finally broke loose. It had a date code from 1999, so it was original equipment. The thing was seized in there pretty good. I made sure and used plenty of anti-seize on the new one. If I'm lucky I'll never have to do it again! Thanks again!