So my girlfriend has a 2004 g35x and its throwin codes p0455 and p0430. The car is high mileage, but I dont know what has and has not been replaced. It drives and idles fine, but her gas mileage has gone down. I know the p0430 is cat bank 2 and the p0455 points at the charcoal canister. Are the codes in any way related?

I drive a lexus gs430 and I once had a p0420 or p0430 code and it turned out to be an exhaust leak, but I also threw in two post cat sensors on it and code has not come back since.

I plan on putting it on the lift and checking for any leaks or visible damage, but can anyone tell me what is a more common fix. Would it be the cats or the sensors? I did a voltage text using a obd2 scanner and my first test looked like this

o2b1s1 0.300
o2b1s2 0.120
o2b2s1 0.590
o2b2s2 0.670

after driving it some more and coming to a stop i check it again

o2b1s1 0.300
o2b1s2 0.200
o2b2s1 0.610
o2b2s2 0.220

Just trying to get some opinions before I start throwing money in this car. thanks in advance.