After I read all posts I started replacing O2 sensors for the first time on 2003 Motero Limited.
According to dianostic codes, I have bad sensors on Bank 1. I got OEM parts and identified the locations on driver side (US). Knowing the condition (heat, rust, age), I sprayed penetrating solvent and left them over night. I got a removal tool (generic 7/8" = 22 mm) , warmed up a little, and ready to work on them. But they do not turn. I stopped before damaging the nut. The tool seems to be a little loose on the sensor.

Am I missing something? Any tips? I know it is not easy to reach these sensors. Should I remove something before work on them?

I really cannot afford $1,800 quoted by my dealership.

Any advice would be appreciated. Thank you in advance.

 

Soak it again for 15 mins at least and use a breaker bar ( length 17 -24 inch). I had problem with seized bolts of front brake calipers. I used penetrating oil and a breaker bar. You may want to one with a ratcheting head. Dealers will use a powerful tool called impact wrench for the job.

 

I tried all those. Impact Wrench?? It will not reach O2 sensors unless exhaust manifold is removed from the engine.