I was digging through the TIS Network and for the life of me I can't find any bloody information on what the fuel economy display is using for a reference.
So I went through the literature and owner' manual, Toyota does not want you to run your vehicle below 1/4 of a tank. There is no real literature on when the Empty light turns on but some calcuations and playing with the numbers revealed to me some interesting points.
-The Fuel Economy reading reaches Zero when the light turns on.
-Toyota does not want the vehicle to run below 1/4 of a tank
-The Fuel Economy reading is almost always innacurate with no option to calibrate it
-Our fuel tanks are 23 gallons
The last one is a vey important detail.
The truth is that the Fuel Economy reading is accurate, as is your hand calculations; to a degree. Here's why:
Lets say you fill up the gas tank about 20 gallons and then start driving, your display will reset and probably read roughly 300-ish miles until empty. Lets also assume that your current and future MPG will be 14.0mpg. So here's how the numbers break down...
14*23=322
14*20=280
But your display will never show you 322mi until empty, infact it will show something closer to 308.
14*22=308
Now here's the tricky part, your FER (I am getting tired of writing it out...) is going to drop drastically in the first couple dozen miles as the computer adjusts to what your mileage reading is. So now your gas tank is empty and you need to fill up again, hit up the gas station and pop in another 21 gallons into the tank, pull out your cellphone and jot down the numbers. (We'll just say 310miles)
310/21=14.8
But you check your nifty FER and it says a solid 14.0!? The reason behind this is simple, your FER stopped counting after 266miles. Now where did I get 266 from? Its what the FER uses as its standard for calculating gas mileage. Remember how I said Toyota said they do not want you to run under 1/4 of a tank? They meant it and designed the information system to reflect that.
266/14=19
19/23=83%
Toyota designed the fuel system to turn the "Fuel Empty" light at roughly 19 gallons of fuel spent. Giving you a roughly 8% margin over their reccomended 75% of fuel to be used. Since they don't want you to run the vehicle below their 19 gallon limit, the fuel mileage computer stops counting after 19 because as Toyota designed it, it is not supposed to be driven past 19 gallons of fuel devoured.
Basically all in all, if you want your fuel mileage computer to match your hand calculations, refill your gas tank before the little orange light comes on. Simple as that, if I find anymore information or work arounds to calibrate it, I'll let you guys know.
PS- For those of you who are really stingy about your numbers, I would assume that the correct number is in fact 72Liters or 19.0204 gallons. Honestly though its close enough IMO to not be needed.
