O2 Sensor B1S2 Rusted Nut

First of all I just want to say fuck O2 sensors, what an absolute PITA to do. Replaced B1S1, B2S1, B2S2 yesterday, upstreams are a horrible job that I never want to do again. Ever.
Anyway, my Bank 1 Sensor 2 is rusted on there. The 12mm nut is rounded due to rust or shitty previous owner and since Toyota put these sensors in the most inconvenient possible positions, it's already almost impossible to reach in there with just a small wrench.
I don't currently have a B1S2 code but I had a P0031 and wanted to replace all my sensors while I was down there. It's frustrating that I could only replace 3/4 sensors.

How do I get this stupid bugger off?

 

If you have some PB blaster to soak it good and small vise grips, you should be able to get firmly locked onto the nut and by slowly, with 1/4 turns back and forth be able to remove the nut. I successful, I would be prepared to possibly replace the stud also. Personally, if I was not making headway, I would have no problem hollering uncle and showing the pic to an exhaust guy and see what they would charge.
YMMV

 

Dremel cutting wheel and a nut splitter. Or you could buy those sockets meant to get stripped nuts off.

 

Um, I hate to say this but you could have saved yourself some money. Those studs are removable and replaceable unless the base holding it broke apart.

 

If that one isn't throwing a code, leave it. I still have one on the truck that I've never replaced.

 

If you leave it long enough it'll just rust off completely. One of mine did that. The other looked like this

Needle nose vise grips got that one off. Or as others said you could just leave it alone if no code. Even if it did throw a code it won't effect the way the truck runs if it's a downstream sensor anyway.

 

You could try a torch and heat the nut cherry red.
Also you might try touching an ice cube to the bolt when the nut is red hot to thermal shock the rust.

 

I had the same issue with mine. The other three were no problem and then that one had me stumped. Luckily, (sort of) my last truck was a bit rusty so I had the tools on hand.
Get yourself some of these in the most common sizes (6, 8, 10, 12) and soak the nut in pb blaster or DW40 and then stick this on your socket and crank it off. Sometimes you need the next size down and you have to hammer it onto the nut, but this took the rusted nuts off like it was nothing.

https://www.irwin.com/tools/screw-bolt-extractors/bolt-extractors

 

The way to go ^^^

 

Hopefully Ben didn't split the wrong nuts

 

Life gets in the way of working on the truck, but I will try the needle nose pliers and then split some nuts when I have the time. Main worry is if I can even fit the tools in the tight space.

 

If so, he'd be singing soprano. Not that it's a bad thing since we do have punk rock bands like "left nut".

 

I cannot for the life of me figure out how to get needle nose vice grips in that tiny space to get a good purchase and twist. Much less fitting any other tool to cut it out. You guys must be wizards. I've decided to leave it for now. It's unsatisfying but will have to do.

 

Eventually the nut will disintegrate and you can just yank it off. I left the shields off for the 2nd time doing it to get better access. I don’t see why the Irwin bolt extractor wouldn’t work for you.

 

It would definitely be nice to have in my arsenal, but with this particular job of B1S2 sensor it's excessively difficult to get anything in there, much less hammer on a sized-down bolt extractor.
Like I said earlier either I'm a dumbass who can't figure out how to get something in that little space to effectively move anything, or you guys are wizards. Probably both.