Post-Cat O2 Sensor Seized and Stripped

Started by Dagnet, May 15, 2024, 04:13

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Hello, I've been trying to fix this issue for a while now and with the MOT coming up soon I need some tips to get it fixed.

The post-cat O2 sensor was stripped after I tried a wrench to loosen it (there wasn't enough space for my O2 sensor tool). Big mistake. Now the nut is too rounded to fit the correct O2 sensor removal tool.

I've tried using penetrating oil, blow torch and mole grips. Although I'm able to get a good grip with this method, it won't budge.

Took the car to an exhaust shop and they said "they wouldn't touch it" because it is "rear-engined". Interesting... What have mechanics become these days??

Thinking if worst comes to worst I'll order a new main-cat and replace the O2 sensor that way. But I fear the 3 amigos will potentially be a bigger PITA if the bolts are like the others on the car lol (fortunately the car is clean from structural rust, 110k miles W-reg).

If you have any tips for trying to remove this it would be much appreciated.


To deal with the existing cat:  Cut the end off the O2 sensor, so you can get a standard impact socket on the thing, heat, plus gas and breaker bar!

I would recommend getting an approved type cat from Cats2u.  The three amigos can always be dealt with, even if it means drilling out studs and using nuts and bolts.

An original cat will be close to the end of its useful like anyway.

Do get OEM crush rings, the aftermarket ones are bobbins.

Perry Byrnes Memorial Award 2016, 2018.  Love this club.


Have you tried warming up the pipe and then spray some plusGas and then undo it?


Socket tool sucks for the post-car O2 sensor as you can't get an angle on it to get a clean fit AND good leverage on it at the same time....

I ended up giving up rather than risk damaging something and bought a nice fat 22mm spanner. With the right tool, I undid it in 10sec.
Black 2006: AC & heated leather: 4x Megillian braces, Koni/Tein custom suspension, MTEC+YS+braided brakes, Toyosports manifold, TTE exhaust, Conti PremiumContact2(summer)/ Conti TS860S(winter) / YokoAD08RS (track/summer), Pioneer MVH-390BT + TS-E171ci, FBSW, Robbins mohair hood.


Had the MOT test today and the EML for the post-cat O2 sensor didn't turn on (usually takes around 50-100 miles after reseting ECU). And it passed emissions. But it failed other areas I didn't expect! Looks like removing the O2 sensor will have to wait another day lol.