What does DEF mean for diesel vehicles?

[BrandonAnn]

DEF in diesel vehicles indicates that the vehicle's urea is nearly depleted, reminding the owner to replenish the diesel exhaust fluid as soon as possible. DEF, known as Diesel Exhaust Fluid, is a consumable required in SCR (Selective Catalytic Reduction) technology. It is a liquid used in SCR systems to reduce nitrogen oxide emissions from diesel vehicle exhaust. Failure to use DEF, or using DEF of insufficient purity or inferior quality, will result in the vehicle's engine automatically reducing speed. Additionally, inferior quality DEF can contaminate the catalyst in the SCR catalytic reaction tank, leading to severe consequences.