Just replace both o2's if you have never changed them, just like a battery they go bad. B1,S1&2 just means bank one meaning a particular side of the eng and if its a 4cyliner then you only have 1 bank. If its a v6 then you have a left bank and a righ bank meaning b1 or b2 . S1&s2 just means sensor 1 or sensor 2 .
replace both, clear the codes drive the car on the highway and around town to complete a drive cycle.