I know it has 2 upstream and 2 downstream.. if anyone knows approx how much it will afffect it .. Let me know...
Abe

Why worry about gas mileage when you should be thinking about how much to rebuild the motor after running it lean?
If both Banks are running lean you may have a bad maf sensor which will also trip codes for front O2 sensors.
Usually only one front O2 sensor will go bad at a time.
You need to read the data list and/or freeze frame information before replacing parts.

It will negatively affect your gas mileage by a lot.

It is the O2 sensor that allows the computer to run on the edge of engine destruction (engine knock). Without it the computer has to play it safe and run rich all the time. This is why the older cars used so much gas (or the newer cars have improved so much on MPG).

Also it depends on which O2 sensor failed. The downstream O2 sensor just checks if the Cat Converter is working or not.


Good Luck...