What is the AdBlue System (SCR - Selective Catalytic Reduction)

Ad Blue Diagram

Most modern diesel cars from 2016 with a Euro 6 emissons will have the AdBlue system.

What is AdBlue?

AdBlue is a colourless liquid that is made from a mixture of high-purity urea and deionized water.

It is important to note that it is NOT a fuel additive and must not be introduced directly into the fuel system!

Adblue has it's own special tank which is usual filled with a seperate filling duct normally located in the boot or next to the fuel filling duct.

What does it do and how does it work?

AdBlue is injected in microscopic quantities into the exhaust system post DPF (the high temperatures turn it into ammonia (NH3)) and mixes with the remaining emissions, it then flows to the SCR catalyst where the chemical reacts with remaining nitrogen oxide gas (NOx) and breaks it down into harmless nitrogen (N) and water vapour (H2O).


Adblue requires refilling a lot more frequenly then the DPF additive and can be done by yourself.

How often you will need to fill is dependant on the type of journeys you make and driving style. On average it's around 6,000 miles and can be brought from any car spare factors or petrol stations.

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