Diesel exhaust fluid (DEF) is composed of urea and de-ionised water and is injected into the exhaust gasses of many modern diesel engines. DEF significantly reduces the amount of exhaust gas emissions and pollution by converting harmful nitrogen oxides into harmless nitrogen and steam.
Most vehicles equipped with DEF will have a dedicated tank that requires to be refilled at normal service intervals. The size of the tank is usually designed so that you should not have to refill the fluid in between services, however individual vehicle’s consumption may be higher depending on operating conditions. The vehicle will not operate unless there is sufficient fluid in the vehicle’s tank.