Ran the engine for a while to test it does not leak. I really wasn't sure but had basically nothing to lose so I applied more force and finished screwing the sensor. Tried inserting the new O2 sensor but when I started to feel the resistance, I removed it and decided to first screw another old O2 sensor into the manifold - for case I damage its thread. I went really slow and after basically three passes I was able to rotate the tap by hand. Then came the worse part of the job - reviving the thread with a tap. The thread of the old sensor was indeed stripped (well, to be precise, its outside half), so the material must have remained in the exhaust manifold's thread. Took me about an hour of slow work with 22 box wrench, vice grip and a hammer (I didn't remove the heatshield). My question is - am I in a danger of stripping the manifold thread if I apply extensive force on the sensor (provided that I won't strip the sensor's hex head)?ĮDIT : After a day of spraying the O2 sensor with WD-40 Specialist Penetrant, I set myself to remove the sensor. I believe they were kind of in a hurry (I asked them to replace the sensor after finishing a long list of jobs and they already had other cars ordered in), so they may have not applied any kind of penetrating oil. They did not want to apply brute force as the thread in the exhaust manifold could be stripped. They were able to turn it only a bit and than it stopped.

The garage I put the car in did not manage to replace it - they told me it is stubborn and that even after applying heat (acetylene burner) it did not come off. One of my two pre-cat O2 sensors is faulty. (2002 Toyota Previa/Estima/Tarago ACR30, engine 2AZ-FE)

Danger to manifold