05 xterra codes p1148 & p0420

Question

check eng lite on replaced bank 1 sensor 1, vehicle seems to work fine but gas mileage not great

Answer 1

HI there

The second code is for the catalytic converter. This could be a factor with the first code to be honest. I would check the catalytic converter on bank 1. You could be seeing that code due to poor burning of the fuel caused by needing spark plugs. If that's the case it can affect the fuel  mileage as well.