The gas mileage in my car is degraded significantly the last three tanks. What should I look for? Details of the vehicle are below, but this question could also apply to anyone who sees this problem with their car.

It's a 2005 Chevy Aveo, about 108,000 miles. I normally get about 32 (which already seemed low for a compact), but recently I'm only getting 23-24, or a 25-30% drop. It's a manual (5-speed) transmission. I'm used to a small drop in mileage as the weather turns colder each year, but even then I still normally make at least 29-30. One other possibly-important detail is that we did store the car for about 6 months last year, but it had been doing well for a few months since we started driving it again (after some post-storage maintenance, of course). It feels like it still has just as much power as it always had, but that is an entirely subjective (unmeasured) observation.

  • Wow. Coming back here today for a different issue, 3 1/2 years later, and I've only put 4,500 miles on the car in all that time. It sure is nice being able to walk to work now. – Joel Coehoorn Jul 3 '15 at 20:04

May be resetting the injection system can help restore things back to normal, usually there is a key sequence to do that.

Considering that the car has the same behavior as usual... look for external agents.

Leaks. Any smell? Stains on the floor where you stop?

Changed gas station? Changed fuel grade? Usual gas station has new owner? Fuel quality may have changed.

Another suggestion less politically correct: can someone be borrowing some fuel from your car?


Bad O2 sensor that the ECU just hasn't flagged yet? Leaking fuel injector?


Have you changed Air Filter or Spark Plugs lately ?. If not, this is the first thing I would do. Then try to use fuel Injector cleaner in your gas tank. If you still have issue, replace your O2 Sensor only upstream. No need to change Downstream (After Cat Converter) once. It is very easy to change it.

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