Diesel exhaust fluid (DEF) is required in diesel engines manufactured after 2010. It’s part of a selective catalyst reduction system (SCR) to reduce harmful exhaust emissions. More than 12 million vehicles in North America require DEF, says Yara International ASA, a Norwegian company that makes and supplies the fluid, including the Air1 brand.
“Continuous and undisrupted supply of DEF is vital,” says Jorge Noval, president of Yara Industrial Solutions, who sells more than 500,000 tons of DEF annually in North America. “Clean air to breathe and a functioning transport sector are fundamental for society. Food supplies, pharmaceutical and hospital supplies — they all rely on DEF.”
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DEF is a critical part of a vehicle’s SCR, which reduces NOx emissions in exhaust. The fluid is injected into the hot exhaust stream from the engine, where it decomposes and releases ammonia, which reacts with NOx in the SCR catalyst, converting NOx to nitrogen and water. The SCR needs proper maintenance to keep trucks in compliance with emissions regulations, including regular additions of DEF, typically at the rate of 5-10% of diesel consumption, Yara says.
To work properly, DEF must contain 32.5% urea and 67.5% deionized water. Urea is also found in fertilizers, animal feed, some medications and skincare products. The urea used in DEF is synthetically produced to automotive standards and is combined with deionized water to make the fluid.
“The quality of the DEF going into your vehicle is as important as the quality of the engine oils or fuels used in your vehicles,” says Bill O’Ryan, senior manager, engine oil licensing and certification and DEF at the American Petroleum Institute (API). “Use of API-licensed diesel exhaust fluid will ensure it meets the high standards required by engine and vehicle manufacturers.”
Ron Schornstein, president and CEO of Acustrip, says if DEF contains impurities, it can cause a loss of engine efficiency, emissions penalties and repair bills. If not properly maintained, a malfunctioning aftertreatment system can shut the truck down. His company makes tests to ensure the proper amount of urea is present, that the fluid is not contaminated, and that the fluid isn’t in the fuel system, which can damage the engine.
He says DEF should be tested each time its refilled.
“Before you put it in, test the tank you’re taking it out of,” he says. There are only a few producers of DEF, he says, but quite a few distributors — and opportunities for contamination.
Old World Industries, maker of Peak and BlueDEF, says impure DEF can clog fuel injectors, block the fuel system, cause fuel contamination and add to build-up in the truck's SCR system. The DEF filter should be changed every 200,000 miles or 6,500 operating hours, the company says. The filter removes crystalized urea and contaminants introduced during storage and handling.
Detroit Diesel recommends using an API-certified DEF that uses ISO standards.
"It is important to source DEF from known and trusted sources since quality can vary and shelf life is limited and can be impacted based on the temperatures it is stored at," says a spokesperson at Daimler Trucks North America, who owns Detroit Diesel.
Off-spec DEF is a common user complaint, Yara says. Improperly formulated DEF will not only perform incorrectly, it also may damage a truck’s SCR system. An improperly functioning SCR system, including one out of or low on DEF, can cause the truck not to start or to go into a limp or low-power mode.
"If it is not added, the aftertreatment system is not able to perform its function of reducing emissions and the vehicle will go into a derate process that limits the speed a truck can move until the tank is refilled," the spokesperson says. "Prior to this happening, the operator will receive warnings to remind them to refill the tank."
Most DEF is good for about a year under the best conditions, and expired fluid can lead to the same performance issues and risks as improper formulated products. That’s why O’Ryan says it’s also important to check how long DEF has been sitting in out-of-service vehicles. If it’s been a year or more, draining and refilling the tank with fresh product is recommended, he says.
“For shops, the handling, storage and dispensing of DEF is very important so that off-spec DEF doesn’t reach the marketplace,” O’Ryan says. “Temperature during transport or at the point of storage or sale can harm the shelf life of DEF sold in containers.”
The API recommends DEF should be stored out of direct sunlight and below 86 degrees. That includes emergency DEF in the truck as well as DEF in bulk storage tanks. Aftermarket additives shouldn’t be added to DEF either, as they could void a warranty, and DEF dispensing equipment should be kept clean and dedicated to DEF to avoid cross-contamination.
