DEF is a fluid used to combat emissions, and thanks to the Environmental Protection Agency (EPA), it is being placed in more and more diesel trucks.
The EPA began releasing legislation to reduce emissions from heavy duty diesel trucks in 2007, Trusted Automotive Professionals Blog reported. Since then, DEF (Diesel Exhaust Fluid) was introduced to more vehicles. It was in the majority of pick-ups by 2013.
DEF is a solution made up of de-ionized water and urea. It is sprayed into the exhaust fumes for the purpose of breaking down emissions and turning the poisonous nitrogen oxide, which causes pollution, into harmless nitrogen and water. The DEF injection system contains a tank, pump, injector, heated DEF lines, nitrogen oxygen sensors, temperature sensors, and a SCR catalyst.
DEF is just as necessary as diesel. If your vehicle does not have DEF or levels of it are extremely low, the vehicle is liable to go into limp mode, begin speed restrictions, and not start up again after it is shut off. To prevent these issues, there is a DEF level gauge on every DEF-equipped vehicle to let you know when you are low or empty on the fluid.
A typical tank of DEF should last approximately a few thousand miles. However, the temperature will also affect how much fluid is used, since the solution is vulnerable to evaporation. Storing the container at 95°F for an extended amount of time will cause the fluid's shelf life to be reduced to 6 months. If it is stored between 10 and 90°F, its shelf life can be one year.
DEF fluid is available at most car dealers, gas stations and supermarkets.