I have not read the owner's manual yet, but I had what I would consider a weird thing happen last night.

The little yellow gas pump began to show up on the dash last night. The needle was on on 'E', but I decided to fill it up anyway. Now, according to the dealer's service dept printout (lists all options), the truck is supposed to have a 26 gallon tank with an extra 7 gallon capacity.

Well, when I filled up, it only took 19 gallons. Even if I had the 26 gal tank, there was 7 gallons left, why did the light come on?

Or is it based upon the number of miles instead of gallons?

 

mine also does this, the manual says it comes on with about 1/8 of a tank left. The bottom of the tank could easily hold 6/7 gallons to be 1/8 full (width & length will hold a lot of gas in a small depth).

 

Mine will come and go on and off for the first 10 miles or so due to turning corners and hills. When it comes on solidly it is at 20 used (about 1/8 tank). I use it as a quick calculator of fuel mileage. Yours sounds about right.

Eric