2008 Peugeot 308 depollution system faulty

the car computer is reading depollution system faulty it also telling the engine that its overheating when it not, also the radiator keeps coming on but before all of this happen i do believe that i got dirty petrol because the car was losing power when driving, my wife car was the same and we where both using the same filling station, change filling station but the problem still the same so too is my wife car, took my car back to the Peugeot dealer he says the sensor needs to be change and he says if its get worse come back and we change it, but you know what i think it more than just a sensor problem, so can anyone out there that knows more about engine than i do tell me what is the cause of the problem because if i can get my car fix in one visit than i can get my wife car fix in one visit too, hope this all make sense, thanks.