Where would I find the O2 sensor on my 2005 Frontier? I want to replace it. Everyone other mechanic tells me it is a bank 1, O2 sensor problem,. The dealership is telling me I need a catalytic converter, bank 1. I already had the catalytic converter bank 2 replace last year. I don't want to make the dealership rich by having me replace something that does not really need to be replace.