Light
Here's the quote from the 2004 service manual:
"Each time the cluster receives messages from the PCM indicating the percent tank full is less than 15, the gauge needle is moved to below the one-eighth position on the gauge scale and the low fuel indicator is illuminated. The low fuel indicator remains illuminated until the cluster receives messages from the PCM indicating that the percent tank full is greater than 15 (one-eighth), or until the ignition switch is turned to the Off position, whichever occurs first."
So the service manual seems to be at odds withitself over exactly when the light comes on, either at 12.5% or 15%. I don't know how accurate the PCM's readings are, but it's probably not accurate enough that either number would matter.
12.5% of 19.5 gallons = 2.4375 gallons remaining.
15.0% of 19.5 gallons = 2.9250 gallons remaining.
So let's assume the worst case scenario, city driving. I'm averaging 16.7 mpg in the city, and assuming the 12.5% number, I can go 40.7 miles before empty. My light usually comes on when the EVIC reads approximately 40 miles to empty.
But I think there is still some idiot proofing built into the system. I usually try to drive 40 miles past when the EVIC reads '0 miles to Empty'. I pushed it to 60 miles past empty once (I had a gas can with me), and I started sputtering, and happened to be passing a gas station and pulled in. I ended up putting 18.9 gallons in, which still meant I had 0.6 gallons left. I could have driven another 10 miles (in theory, assuming the fuel pump is able to pump 100% of the fuel out of the tank)!
This built in idiot proofing may go back to what TJKJ said about burning up the fuel pump at low volumes.
I hate how EVERYTHING, has to be built to function for the dumbest individual. Build it for the average man, and force the stupid people to adapt, learn, do without, or die.