[TrevorS]

Botom line is if you want to know what your actual MPG is, then record your elapsed miles and fill-up gallons at each fill-up and divide the second into the first each time you fill up. The numbers presented by the on-board computer are just an estimate and are anything but reliable. If you care about your real MPG, then you need to manage your driving habits as well as keep on top of your tire pressures.