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You may be guilty. Your check engine light goes on and what do you do? Drive to Dunkin Donuts to think it over? Go home, grab a beer,and tune in to ESPN? Go shopping?

Are you like the millions of Americans who just forget about it?

CarMD.com says 80 percent of vehicles on the road today are in need of service or repairs right now and more than 9 million U.S. drivers alone have ignored their car's "check engine" light for three months or more.

OK, given the state of the economy, it's understandable. The top reason car owners cited for procrastinating is lack of money (65 percent); lack of time (34 percent); and some didn't think it was serious (28 percent). Believe it or not, some (12 percent) were actually afraid to find out what the problem was!

Nonetheless, here's something you need to know; the #1 reason for "check engine" problems is a faulty oxygen (O2) sensor which can reduce your gas mileage by as much as 40 percent.

These sensors monitor oxygen content going through the exhaust system and help your car's computer to constantly adjust the air-fuel mixture to the immediate driving conditions and that has a direct impact on your engine's performance.

Not only will a faulty sensor make you spend more on gas faster than you need to, you won't pass your state's emissions test if you have a 'check engine' light on.

If the problem is your oxygen sensor, it's an easy fix. The guys at Auto Zone say that depending on your vehicle's make and model, it will cost anywhere from $40 to $80 and if you've got the right tools you can probably do it yourself in 10 or 15 minutes.

And, depending on your vehicle, you may need to replace more than one, however, the savings will definitely offset the expense by a great margin.