I'm getting a check engine light and a P1273 fault code on my 04 350z , it's got berk high flow cats , rev up map , pop charger intake filter and scorpion cat back , I'm guessing it's due to an o2 sensor as the exhaust seems to be popping a bit more lately and I'm gettting slightly worse mpg so makes me think it's running a bit rich , need to sort it before the mot as I doubt it will pass emissions like this , anyone got any suggestions where to start ? Thanks