When should they be replaced and are there any performance (MPG) increase in doing so. I have made it to 130K without a problem and pass every engine emissions test. I get 25 to 35 MPG depending on the season and long trips.
Every 60,000 miles your O2 sensor should be replaced. You might get a MPG increase that you might see. It's a new sensor so it switches voltage normal again. Not like an old sensor which switches slow because its always switching.