That's especially true of the low fuel light. READ MORE: Surprising Lost Items From This Year's Sturgis Motorcycle RallyAAA is trying to take the mystery out of the great low fuel light game with their recent article How Far Can You Drive When the Low Fuel Light is ON? Starting at your next fill-up (with your fuel tank full), reset your trip meter to zero or write down your odometer reading, then drive as you normally would. The 2 gallons left over gives us the amount of gas in the tank when the low fuel light comes on. Multiply the vehicle's 23 mpg by the number of gallons left in the tank when the fuel light comes on (2).