I have a 2012 Ford Fusion Hybrid and can tell you that I hunted and hunted for low fuel indication information. Here is what I know to be true, at least for the 2012, because I have seen and experienced it over and over. For mine, the amber fuel warning comes on at 50 miles to empty (DTE), and then anytime you stop and start the car you get the amber warning when you are below 50. You can reset the large amber warning in the upper left of the 2012 display by depressing "reset". But, it will come back on if you stop and start the car or get to 25 miles to empty (DTE) and then 0 miles (DTE). The amber warning at the fuel gauge remains on from 50 miles (DTE) on down. But, the warning is a brighter amber or yellow by the fuel gauge from the normal shaded color telling you your fuel level on the gauge. Now, when you get to the point when there is about a gallon remaining (about 40 miles in my 2012 fusion). The SHADED area that shows fuel quantity, which is just a sliver now and is normally amber/yellow, TURNS RED (kind of like the bottom markers of the other gauges--so easy to miss it). When that comes on, you are operating on the "reserve". Okay, that's all I can tell you about my experience on the 2012. Of course, yours may be mechanized differently on the 2013.