AdBlue
A diesel exhaust fluid (DEF) composed of urea and deionized water used to reduce NOx emissions in diesel engines.
AdBlue is a trade name for a standardized solution of 32.5% high-purity urea and 67.5% deionized water, widely referred to as Diesel Exhaust Fluid (DEF). It is stored in a dedicated auxiliary tank on modern diesel vehicles equipped with Selective Catalytic Reduction (SCR) technology. AdBlue is injected in tiny quantities directly into the exhaust pipe upstream of the SCR catalyst, where it vaporizes and decomposes into ammonia and carbon dioxide.
Inside the SCR catalyst, the ammonia reacts with harmful nitrogen oxides (NOx) in the exhaust stream, converting them into harmless nitrogen gas and water vapor. This process allows modern diesel engines to meet strict emissions standards without compromising engine efficiency or fuel economy.
If a diesel vehicle runs out of AdBlue, the engine management system will enter a restricted performance mode (limp mode) and eventually prevent the engine from starting once turned off, as mandated by environmental regulations. Contaminating the AdBlue tank with water or diesel fuel can ruin the delicate SCR injector and catalyst, leading to thousands of dollars in repairs.