Diesel Exhaust Fluid (Universal)

What is Diesel Exhaust Fluid?

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Diesel Exhaust Fluid (DEF) plays a crucial role in reducing harmful emissions in modern diesel engines. DEF is injected into the exhaust stream during diesel engine operation to begin the process of Selective Catalytic Reduction (SCR). This breaks down harmful nitrogen oxides into water vapor and nitrogen; both harmless, environmentally friendly substances. SCR is an effective way to reduce emissions and is required on vehicles originally equipped with DEF systems to adhere to environmental regulations. Diesel exhaust fluid is designed to not only minimize the impact of diesel emissions on air quality, but also helps improve engine performance and fuel efficiency. Low levels of DEF can cause noticeable, potentially damaging effects, including a reduction in engine power or a complete shutdown of the engine.

Is DEF Required in Diesels?

Though older diesel equipped vehicles did not require the use of a DEF system, nor were they set up to utilize it, Selective Catalytic Reduction technology was mandated for all diesel vehicles beginning with the 2010 model year. Vehicles made after this time are required by federal law to be equipped with a functioning DEF system and DEF needs to be added to the vehicle frequently to ensure efficient operation. Most vehicles will have a gauge or warning light that indicates the DEF level or alerts you when DEF levels fall especially low. The vehicle may also engage limp mode or reduce performance drastically when the DEF system is empty, which means it may be a good choice to keep a supply of DEF in your vehicle for unexpected circumstances.

How Often Do I Need to Add DEF?

Typically, one gallon of DEF can supply a diesel engine for up to 500 miles, but it is a good idea to keep it on-hand to prevent running the DEF reservoir dry. A general ratio of DEF usage is about one gallon of DEF per 50 gallons of diesel fuel so keep an eye on your fuel consumption and add exhaust fluid to the system periodically to ensure your diesel engine continues to run at its best. If you are performing routine maintenance such as winterizing your diesel or replacing a diesel fuel filter or if you simply want to learn more about the purpose of DEF to keep your diesel running as it should, visit our How-To Hub for informational articles and step-by-step videos.