[alanfreeman]

I agree with 3Wheelerguy. You probably need to reset your MPG every time you refill your tank. On the older Siennas, go to the MPG display and then press and hold both the E/M and MODE buttons for about 5 seconds. On the 2015, you would go to the MPG display screen and press and hold the DISPLAY button for about 5 seconds. You can look this up in your manual, if it is different for your model and year. As you drive, it will adapt to your driving habits and be more accurate. REMEMBER, do this every time you fill up your tank for a more accurate reading because as your air filter and oil gets dirty, it may change. That number also changes based on driving habits. If you stop quick, race up to speed, and vary your speed often, it will be less. Don't forget that other drivers of that vehicle can effect that number as well.