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Diesel Exhaust Fluid (DEF) is a solution of urea and water that's injected into the exhaust stream of diesel vehicles to turn NOx gases (harmful emissions) into nitrogen and water.
In short, it's basically a secondary "fuel" that isn't actually "fuel", and the annoying thing is that if you run out your vehicle will be put into a limp mode until you add more DEF. It was created mainly to reduce emissions, and while some auto manufacturers have started circumventing it with better engine designs a lot of trucks/tractors/other types of diesel vehicles still need it.
Worth noting is that US government vehicles are exempt from the DEF requirement no matter how much pollution they generate.
DEF consumption is usually 2-3% of diesel consumption, if you use 100 gallons of diesel you'll need 2-3 gallons of DEF.
In short, it's basically a secondary "fuel" that isn't actually "fuel", and the annoying thing is that if you run out your vehicle will be put into a limp mode until you add more DEF. It was created mainly to reduce emissions, and while some auto manufacturers have started circumventing it with better engine designs a lot of trucks/tractors/other types of diesel vehicles still need it.
Worth noting is that US government vehicles are exempt from the DEF requirement no matter how much pollution they generate.
DEF consumption is usually 2-3% of diesel consumption, if you use 100 gallons of diesel you'll need 2-3 gallons of DEF.
