Depends on how you drive. But you run that low on fuel too many times and you will be replacing the fuel pump. Never run a fuel injected vehicle below 1/4 of a tank or the fuel pump starts picking up sediment from the bottom of the fuel tank. Also keeping at least 1/4 of a tank of fuel in the tank helps keep the fuel pump from overheating. The warning signal will come on when you have about 3 gallons of fuel left in the tank. If you have the owner's manual to your vehicle it would tell you this.