This is for the rust belt owners! Seriously, looking at pictures of some cars without ANY rust it makes me want to live somewhere less moist shall we say. You'll not experience the oxide blues....

Upper O2 sensors should be a 1-2-3 job, my latest hasn't been that straightforward. I flooded this one prior to trying to get it out for a few days with penetrative oil, then used a 3/8th 22mm O2 socket on a warmed up cat, a bit of torque and the socket opened rounding the O2 nut......didn't expect that.

Back with a 1/2" drive version with an 8mm slot for the sensor lead instead of the 20mm on the 3/8th - same thing, opened and rounded.

I've removed sensors with these sockets on these cars before now, so I doubt it's the tools more likely this one was in good and tight.

The third attempt I decided on a long reach 22mm spanner, basically last chance before I'd remove the cat from the exhaust manifold, a horrid job because the studs snap off.

Nipped the grey connector off. Gave it a tiny tighten and it moved so swung it the other way and it was easy out.
I'll not bother with the sockets on the uppers from now on, just cut the dead sensor's connector and use the BFS!

 

Yes sir, those deep well open wall sockets can enlarge with enough torque, and you have proof.
Nice to have a Snap-On 22mm as a backup! I cannot quite make out the branding on yours but
it seems to have the same ultra-chrome finish.

 

The only thing I've found to consistently work on these is to heat the everloving hell out of them. if its all kinda rounded, a pipe wrench will get a good grip.

 

blue wrench

induction heater

 

I torched the bung with mapp gas for a bit and then sprayed a cooling penetrant on the nut part of the sensor, with the leads snipped off a 22mm box wrench fits right over it and a second wrench on the tip for added leverage and the sensor came right out. I try to not bother with the slitted O2 sensor sockets as they don't hold their shape well an tend to open up and rui the flat surfaces on the sensors.

O2 sensor on my 2004 Sierra...now that was a challenge...had to cut it down to just a nut with an angle grinder (since the sawzall wouldn't fit in there) and then use my 1/2" cordless impact gun with a couple extensions, a wobble and an impact socket...killed one of my batteries before it finally started to come out....but it came out

 

Those O2 sockets are good but they are easily flexing too. I have to weld a piece of thin steel to the low section of the socket to prevent flexing. This works when the sensor is broken anyhow that you can cut the connector off.

 

Yes, another method to prevent said flexing is to use a hose clamp at the end. One mechanic I know
uses a vise grip on the end. to get it started.