Since I live in cold Quebec Canada, I never let it get that low. Causes vaporlock often due to low gas in tank. Costs the same to top off at 1/4 and cheaper than having a fuel pump seize up due to inhaling fumes/air and not cooling down via submerged in gas for cooling. Keep that in mind.
I know vapor lock happens more in high hest temp conditions, maybe I am using wrong term, but when tank is very low, causes condensation that can freeze up and cause a no start. Most likely though, more harm to fuel pump from sucking air and not fully immersed in gas.
Not my writing
Why You Shouldn't Let Your Gas Tank Run Low
Are you one of those optimistic drivers who doesn't worry about stopping for gas until the gas gauge needle is approaching 'E'? In cold weather that's inviting trouble, says the Car Care Council. Condensation of moisture in the air in the gas tank causes an accumulation of water. Because water is heavier than gasoline, it settles to the bottom of the tank, entering the gas line and eventually working its way to the lowest point in the fuel system.
Once the moisture freezes, the fuel flow is blocked and the engine may not start on a cold morning.
Most brands of gasoline are formulated to prevent freezing, says the Council. Additional protection in the form of gas line antifreeze, however, can prevent starting trouble in severe cold. This methanol (methyl-alcohol) based product, found among automotive chemicals on most auto supply shelves, mixes with water to prevent freezing. The solution of gasoline, alcohol and water is burned in the engine's combustion process.
Some premium brands of fuel antifreeze products contain isopropanol, capable of absorbing five times its weight in water.
Consider other reasons for not allowing the gas tank to drop too far below half full.
First, and most obvious, is the possibility of running out of gas in an area where no service stations are available.
The other reason, less obvious, applies to fuel injected vehicles on which the fuel pump is located inside the gas tank. Cooled by the gasoline that surrounds it, the pump can be damaged from overheating when the fuel level is too low.
It costs no more to keep a tank at least half full, and the addition of fuel line antifreeze is a small price to pay for the added protection it affords.
Beyond this, because a battery loses some of its output in cold weather, be certain it's OK for another winter's use. Finally, concludes the Council, make sure your engine has adequate antifreeze/coolant protection and that the spark plugs and ignition system components are up to the cold weather challenge - it'll save you down the road.
This only goes to say what I am writing. Disregard vaporlock term, I really meant condensation.
Tell us why it is important to you, maybe we can come up with better advice. When that light comes on, that indicates a certain amount of fuel left. Even if you find out how many gallons/liters that is supposed to be, we can't tell you how many kilometers you would get. That will depend on your mileage in that particular vehicle with your particular driving conditions/habits.
@billr, maybe fuel gauge went south and now the car only has idiot light to remind the op that gas is now at crucial level. I have seen this before. We here can only assume something like this. ouch
I am also assuming most sedans have 10 liters to 15liters reserve after idiot light nicely tells you that your stuck because the next gas station is 200clicks away :ROFL. At 100km per hour, and optimum mpg of 8 liters for 100km average, also assuming the tune up is top notch, I would be hard pressed to give any other info than just hint at something most owners manuals will say anyway. DO NOT RUN ON A LOW GAS TANK.