Hope someone can help. My 2009 308 1.6 Petrol failed its MOT in December on emissions so garage replaced CAT (with aftermarket one I think) and Lambda sensors. Prior to the MOT there were no errors displayed. Car worked fine for 2 months now it has come up with the infamous antipollution error with a P0420 code indicating ageing cat. With the error on, the engine runs a little lumpy and when the error is reset it runs fine again. Is it possible that within 3 months the car needs another cat? Anyone got any suggestions as to what I can do?