Poor fuel economy
A sudden rise in fuel use often follows a mixture, sensor, or catalyst code rather than a vague “bad mileage” fault.
A lean code such as P0171 can mean unmetered air. A rich code such as P0172 can mean extra fuel. P0420 points at catalyst efficiency, which sometimes shows up as higher consumption after other faults.
Compare fuel trims and the stored code before replacing pumps or the catalyst. The DTC pages list the usual checks.
A trouble code marks a condition to test. It does not by itself prove which part to replace.