Diesel Exhaust Fluid (DEF)
Diesel exhaust fluid is one of the key elements of the Selective Catalytic Reduction (SCR) process used by most medium and heavy-duty engine builders to meet EPA 2010 regulations.
DEF is not a fuel or a fuel additive. Instead, when injected into the exhaust stream and passed over a catalyst, DEF helps convert NOx into Nitrogen gas and water vapor – two harmless and natural components of the air we breathe.
Making sure you do not run out of DEF in a SCR equipped truck is simple – watch the DEF gauge, which is part of the diesel fuel gauge, for when it is time to refill.
DEF is stored in a dedicated tank next to the fuel tank on the driver’s side. The tanks range in size from 6 to 23 gallons depending on the truck’s application. The DEF tank fill opening is designed to accommodate a DEF fill nozzle to ensure only DEF is put into the tank. A diesel fuel nozzle will not fit into the DEF tank opening.