[ny_transplant]

Hi all. I am new to the board after purchasing a 2005 SR5 4x4 w/37k miles. Been lurking awhile and enjoy the wealth of information found here.

My main issue is the gas mileage. On a full tank, the overhead display has consistently shown less than 290 miles when I fill up. I am getting around 12 mpg based on the display.

Spoke to the dealer about the poor mileage and was told that the oxygenated gas is the cause. But can that cause a drop of 20%+ from an expected 15+ mpg mixed driving down to 12 mpg?

I've read about the oxygen sensors, and trying to figure out what condition has to be met for the check engine light to come on due to O2 sensor failure? Does it have to be a complete failure, and could mine just be fouled and need replacing? How do I approach dealer to get this replaced under warranty or should I just go ahead and replace all four?

Thanks.