Diesel Exhaust Fluid (DEF) is a consumable liquid made of 32.5 percent high-purity urea and 67.5 percent deionized water. It is injected into the exhaust pipeline of diesel engines equipped with Selective Catalytic Reduction (SCR) systems. The exhaust heat breaks the DEF down into ammonia, which reacts with harmful nitrogen oxides over a catalyst, converting them into harmless nitrogen gas and water vapor.
Heard on the job
The truck is stuck in limp mode because the DEF tank ran completely dry.
Insider tip
DEF freezes at 12 degrees Fahrenheit, so vehicle tanks have built-in heaters to thaw the fluid in cold climates.
Also heard as
- diesel exhaust fluid
- AdBlue