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What is AdBlue?

AdBlue is a non-toxic, non-flammable, odourless and biodegradable reducing agent that helps to make cars cleaner and more efficient, meaning lower levels of harmful car and van exhaust emissions such as Nitrogen Oxide (NOx).

AdBlue works with a treatment system called ‘Selective Catalyst Reduction’ (SCR), which converts nitric oxide into less harmful nitrogen and water. It is made by mixing a compound made from ammonia and CO2 into deionised water.

The AdBlue fluid is not mixed with the fuel in your vehicle but carried in a separate tank and then pumped into the engine where it is injected into the exhaust gases. Working together with the catalyst, Adblue converts 80% of the NOx coming from the vehicles combustions chambers into harmless nitrogen and water.


AdBlue is a key ingredient in certain Audi diesel models system that helps reduce nitrogen oxide emissions – and, just like the oil in your engine, it must be kept at the right level. If you need it, you’ll have an AdBlue filler cap under your diesel filler flap (or in the boot on older models).

Your Audi will warn you when you’re within 1,500 miles of needing to top up your AdBlue, and it’s vital that this is done – either by you or your local Heritage Audi Centre – to ensure your engine keeps working as normal.

Consumption will depend on driving style, journey type, road conditions and the load placed on your engine, so topping up your AdBlue tank may be required between services.

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