Diesel Exhaust Fluid (DEF)

Diesel exhaust fluid (also referred to as DEF or AUS 32) is injected into the diesel exhaust stream and the heat from the exhaust, the fluid, and a catalyst convert the NOx into the harmless gases.

Diesel exhaust fluid is a 32.5% solution of technically pure urea in purified water. For the SCR unit to operate properly, the DEF must meet an exacting purity standard. This standard, published by the International Organization for Standardization (ISO), is intended to ensure that the diesel exhaust fluid used in SCR-equipped cars and trucks provides the purity required by diesel engine manufacturers and the quality to preserve the emissions control system and the environment.