It's good to know how much gas you have. Your car lets you know with a fuel gauge. A little float made of foam sits in your car's gas tank. The float bobs on top of the gasoline; the higher the gas level, the higher it floats. The float is attached to a thin metal rod that scrapes up against playing a resistor, which sends an electric signal to the fuel display. The signal comes from your car's battery via a small coil. The lower the float drops, the more current the resistor sends to the fuel gauge and the closer you get to "E" for empty. Of course, today's cars make it even harder to come up with excuses for running out of gas: The car might turn on a low fuel light and often an audible signal when you get dangerously low -- or even estimate how many miles you have to go before walking to work instead of driving in the comfort of your car.
Gas gauges don't fail often, even if we seldom trust them. When they do fail, the problem could be in the float and resistor system located in the tank, in the dash gauge readout or in the wiring between the two. There are some ways to tell what might be causing the problem: Poor grounding at the reader in the tank is the most common problem, so it's a good idea to check wiring first. A needle that remains on empty when you know there's gas in the tank indicates battery power is not reaching the gauge; you may need to replace defective wiring between the switch and the gauge. Faulty wiring often is the problem when the gauge simply reads incorrectly, and the source varies depending on how the gauge reads versus how much gas is in the tank [source: Fifth Avenue Tech Tips].
Of course, hybrid and electrical cars may come with a different kind of gauge -- one that measures the car's battery range -- the equivalent of fuel for those running their cars on electrical power. Devices in the first generation of these battery gauges were termed "guessometers" by some owners [source: Nishimoto]. It's possible that someday, all drivers will be watching their battery gauges in real time instead of estimating when the gas gauge will dip to that anxiety-provoking level. As with some digital gas gauges that currently give driving range estimates, electric car gauges do the same with battery charge [source: LaMonica].
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