AdBlue is still unfamiliar to some motorists but owners of modern diesel cars with engines that are Euro 6 compliant will already know about it. Our guide explains what AdBlue is, what AdBlue used for, how it works, how to keep it and what happens if your car runs out of it.

What is AdBlue®?

Adblue (the registered trade mark for AUS32) is a 32.5% aqueous urea solution of high-purity, synthetically manufactured industry grade urea in de-mineralized water.  It is a safe-to-use fluid. If you are in Brazil, this product is called ARLA32. If you are in the US, this product is called DEF (diesel exhaust fluid).AdBlue should meet the  DIN V 70070 standard and ISO 22241-1 specifications and complies with ISO to safeguard the correct functioning of your vehicle's SCR system

What is AdBlue® used for?

It is developed for use in selective catalytic reduction (SCR) systems fitted to diesel engines. The purpose of this system is to reduce nitrogen oxide emissions present in the exhaust gas stream.

How does AdBlue® work?

Vehicles with SCR technology have a separate tank filled with AdBlue. This is then injected into the exhaust pipe, in front of the SCR catalyst, downstream of the engine. 

Heated in the exhaust, it decomposes into ammonia and CO₂. When the NOx from the engine exhaust reacts inside the catalyst with the ammonia, the harmful NOx molecules in the exhaust are converted to harmless nitrogen and water, which are released from the tail pipe as steam.

How to keep AdBlue®?

Adblue can be stored for 1 year, ideally away from direct sunlight and temperature extremes.

Its freezing point is at -11°C, and upon thawing returns to initial quality. It should be stored in a sealed package in a well ventilated storage area.The product is slightly alkaline with a pH of approximately 9.0 so should not be kept in contact with aluminum, brass, mild steel. Stainless steel and plastic tanks and fittings are recommended.

What happens if the car runs out?

Since a full tank of adblue can last up to 10000 miles, running out of AdBlue is a bit unlikely. But, before running out your car will display a warning when the tank is almost empty. This warning, which will appear as a warning/light on your dashboard, indicates that you have around 3 liters of Adblue left, which are enough for 1200 miles, or so.

Don’t ignore this warning because if you do, when the adblue tank will be over your engine’s performance will be greatly reduced. More importantly, if you stop the engine, it won’t start again if the adblue tank is empty. Only in 2017, there were more than 20.000 reports of AdBlue breakdowns.