2021 Chevrolet Tahoe Diesel Engine
Photo: Chevrolet
If you drive a diesel-powered vehicle, you’ll have some unique maintenance tasks to keep track of. Unlike gas-powered cars, diesel trucks have a smog-cutting system that sprays diesel exhaust fluid, abbreviated as DEF. Here’s a look at what you need to know about DEF.
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What does DEF do?
DEF cuts down on the pollution produced by diesel trucks. When diesel fuel combusts, it produces toxic chemicals called oxides of nitrogen, often abbreviated to NOx. DEF is sprayed into the exhaust, causing a chemical reaction that turns dangerous NOx into harmless nitrogen.
Most DEF is made from two-thirds purified, deionized water, and one-third urea. If you’re one of the rare diesel-truck-driving vegans out there, rest assured that the urea used in DEF isn’t derived from animals.
How much DEF do you need?
Generally speaking, you won’t need to fill up on DEF every time you refuel. Most trucks use about 2.5 gallons of DEF for every 800 miles of travel, but your truck will burn through its DEF reserves faster if you’re hauling a heavy load.
Is DEF dangerous?
As mentioned above, DEF is made of urea and water. Urea is common a substance that’s made from ammonia and carbon dioxide. It’s a widely applied, found in medicine, animal food, fertilizer, and some household cleaners. It’s used as a browning agent in factory-made pretzels, and it’s even used as a pet-friendly alternative to de-icing rock salt. While you certainly shouldn’t consume DEF or rub it on your skin, it’s less dangerous than many other automotive fluids, such as fuel and antifreeze.
What happens if you run out of DEF?
If your truck is running low on DEF, you’ll be tipped off by a warning system. If you run out of DEF, you truck will enter “limp home” mode, which reduces its power output and may even limit how many more times you can switch your vehicle on before it becomes unresponsive. So if your truck gives you the low DEF warning, treat it like you’re running low on gas, and top off the tank as soon as you can.
Where can you buy DEF?
With the growing popularity of diesel trucks, DEF isn’t hard to find. DEF can be purchased at auto part shops, some gas stations, and virtually all highway truck stops. You can also look for it in the car care section of major big-box retailers.
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Looking to do more DIY car care? Learn more about critical car fluids.
Kimiko Kidd is a native Daytonian. She graduated from Wright State University with degrees in environmental science and sociology. She loves her trusty old Honda Civic, but dreams of owning a 1974 Ford Falcon XB with a custom paint job and a vintage Kawasaki Z1000. In her free time, Kimiko can be found watercolor-painting, baking muffins, collecting rocks, playing old-school Nintendo games, writing her novel, sewing stuffed animals, and cosplaying as her favorite Mad Max characters. See more articles by Kimiko.
