Low Fuel Lamp/Indicator: Description and Operation

A thermistor is mounted in the fuel tank unit. When the thermistor is cool, its resistance is very high. When the thermistor is warm, its resistance decreases. Fuel in the fuel tank transfers heat away from the thermistor fast enough to keep it cool so the thermistor's resistance stays high and the low fuel indicator light does not come ON. When the fuel level drops below about 2.2 gallons, the thermistor is no longer immersed in fuel. Without the fuel to cool it, the thermistor's resistance decreases, allowing current to flow through the low fuel indicator light and the thermistor to ground, and the low fuel indicator light comes ON.