DEF stands for Diesel Exhaust Fluid. It is a 32.5% solution of chemically pure Urea and 67.5% demineralized or deionized water.

What does DEF do?

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. This system is called a Selective Catalytic Reduction (SCR) implemented by vehicle manufacturers to meet EPA emissions standards in 2010.

What does DEF level mean?

What DEF is, at a chemical level, is a combination of deionized water and urea that transform harmful nitrous oxide emissions into harmless water and gas. ... As this emission standard has increased to include off-road vehicles, generators and a variety of engines, DEF is being used now more than ever.