Just sharing my experience - recently I received error P0420 which indicates deteriorated catalytic converter. The light came back a few days after I erased the code. 2007 car with 172tkm (107t miles). I decided to change the O2 sensors as I learnt that they should be preventively changed in 160 tkm due to their laziness they build over time.
After the change the error is gone and the car is considerably more agile. Both Denso direct fit sensors together cost some 130 USD here. The upper one went out quickly while the one down the cat was a bit harder. Still - I used the WD40, a special nut, ratchet and a piece of pipe and it went off, even from a cold exhaust pipe. I was getting ready for some serious battle (even bought a torch for this) but in the end it was not necessary. Yay!
Btw I do not think that cleaning it with a wire brush is a good idea. The sensor is inside a metal cap, you can never reach it with the brush. And even if you do - you will destroy it.
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