Not sure on km, but on my 04 after filling the tank up after the warning light came on, several times, the pump would say, I only put 20.. la la amount of gallons in, so I still had about another 2 gallons left, which would be maybe good for 30-40miles...
I used to only tank up when I'd get the 'low fuel' on my 04 and I think I was putting in an average of 20.5 gallons. I remember driving beyond that mark about 30 miles once.
carry a 2 gal can of fuel in the bed, and drive it until it runs out to truly find out how your trac behaves. the low fuel light comes on differently depending on trac, stance, going uphill or down, smooth or bumpy roads...
When my low fuel light comes on I have only about 1 gallon left. I talked to the service rep about it a while ago and he couldn't give a definitive answer as to how many gallons remain. He did tell me Ford had many complaints from people who had 4 or 5 gallons left when the light came on so he thought Ford lowered that number. I would rather have 4 gallons left that only one.
In my '07, it comes on at a quarter of a tank. Furthermore, if I run all the way to "E," I can only put about 16.5 gallons in my 22.5 gallon tank. My gauge lies.