AdBlue DEF explanation from Wikipedia, the free encyclopedia AdBlue DEF – Diesel exhaust fluid Diesel exhaust fluid ( AdBlue DEF ) is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. Therefore it is standardised as AUS 32 (aqueous urea solution) in ISO 22241. DEF, used as a consumable in selective catalytic […]