‘04 Tundra 4.7 186k in rust belt western PA with original downstream O2 sensors. I think my bank 1 side failed because I’m getting a P0420 bank1 catalyst below threshold but the Cat seems ok. (No loss of power or mpg, downstream side is 20 to 25 degrees hotter on infrared temp scan). My exhaust looks pretty solid even around that area all things considered. My question is how hard are they to remove? Can I expect to ruin something? I soaked it this evening while hot with PB Blaster. What wrench do you use? My slotted 7/8” socket that I think I bought for another O2 sensor somewhere along the line is too big. 19mm open end that I used just to check for size didn’t seem to fit. Relax, I didn’t try to loosen it with an open end wrench. ; ) The connector did come apart easily though.