Peugeot 308 exhaust sensor

hi everyone got a problem hopefully some of you can advise first of all got my exhaust senor before cat replace and about two hours later my engine management light can back on and the reading depollution system faulty just as before, during all of this i purchase a ms300 Obd 2 code reader great little thing recommended but anyway, and these are all of the code its reading, PO131, p2195 p, p1648, p1448 p, now got my car services about four months ago from the same peugeot dealer and this problem started about two month back, now what i need to know is this garage trying to pull a fast one on me the reason why i ask is because if you change a faulty sensor with a new one then the problem should be solve, and reading up on other website i came across this little piece, (When my O2 sensor went, about four lights on the right side came on. It happened after I had my car serviced. Apparently the tech failed to make some kind of modification) my last question is if this is true then did my sensor need to be change at all, the old saying is if you don't ask you wont know, thanks.