Diesel Exhaust Fluid (DEF), also known as AUS 32 or AdBlue, is a non-toxic, clear, and colorless liquid composed of 32.5% high-purity urea and 67.5% deionized water. It’s not a fuel additive, instead, it's stored in a separate tank in vehicles equipped with Selective Catalytic Reduction (SCR) systems.When it comes to choosing the right DEF,&n