top of page

DEF Information Q & A


Q: What is DEF®?

A: DEF is Fluid (known as Diesel Exhaust Fluid) that is used in Selective Catalytic Reduction (SCR) systems on diesel engines to reduce NOx ( Nitrogen Oxide).

Q: What is Selective Catalytic Reduction (SCR)?

A: SCR is an acronym for Selective Catalytic Reduction. SCR is a technology that uses a urea based diesel exhaust fluid (DEF) and a catalytic converter to significantly reduce oxides of nitrogen (NOx) emissions. SCR is being used by almost all OEM manufacturers.

Q: What is the composition of DEF?

A: DEF is a high-purity, 32.5 strength urea solution and deionizer water. Urea is a compound of nitrogen whose aqueous solution generates ammonia when heated. It is used in a variety of

industries, including as a fertilizer in agriculture.

Q: What is the freeze point of DEF?

A: A 32.5% solution of DEF will begin to crystallize and freeze at 12 deg F (-11 deg C). Freezing does not harm the quality of the DEF solution. Upon thawing, DEF will perform as required.


Q: Are there any quality standards DEF must meet?

A: Yes, DEF needs to meet the ISO 22241 quality standard. Defined by AUS-32 specifications to meet or exceed the DIN 70070 August 2005 quality standard, the DIN V 70071 June 2005 analytical standard. The American Petroleum Institute has developed a quality certification program that ensures North American supplies of DEF will meet these standards at the pump and across the nationwide supply chain. This includes manufacturing, handling, safety and environmental protection.

Q: Is it hazardous, toxic or flammable?

A: No, DEF is classified as non-hazardous, non-toxic or flammable.

Q: Is DEF corrosive?

A: DEF is corrosive to copper and brass as well as other materials. Only approved materials as listed in the ISO 22241 standards should be used in contact with DEF.

Q: What happens if the vehicle runs out of DEF?

A: The vehicle power will be reduced to encourage the operator to refill the DEF tank. Once the DEF tank is refilled, normal power levels will be restored on the vehicle.

Q: Does DEF mix with fuel?

A: No, It is not an additive. It is sprayed into the exhaust stream where it reacts with the NOx in the SCR system to form Nitrogen and Water.

bottom of page