AdBlue & DPF
What is AdBlue
What does AdBlue do?
CheckFuelPrices Editorial
Expert Written • 4 industry sources
AdBlue is a diesel exhaust fluid that neutralises harmful nitrogen oxide (NOx) emissions produced by modern diesel engines. It is injected into the exhaust system, where it converts NOx gases into harmless nitrogen and water vapour before they leave the tailpipe.
How AdBlue Works
Selective Catalytic Reduction (SCR):
AdBlue is sprayed into the exhaust stream and reacts inside an SCR catalyst. This chemical reaction breaks down NOx — a major contributor to air pollution — into nitrogen and water vapour.
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What AdBlue is made of:
AdBlue is a precisely mixed solution of 32.5% urea and 67.5% deionised water. It is non-toxic and non-flammable, but it must never be added to the fuel tank.
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Stored in a separate tank:
Vehicles fitted with SCR systems have a dedicated AdBlue tank, separate from the diesel tank. Most cars hold between 10 and 20 litres, which typically lasts 5,000–10,000 miles.
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Why AdBlue Is Required
Euro 6 emissions standards:
AdBlue systems became common as manufacturers needed to meet strict Euro 6 NOx limits introduced for diesel vehicles from 2015 onwards. Most modern diesel cars, vans, and lorries now use it.
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MOT and emissions checks:
Tampering with or removing an SCR system is illegal and will cause an MOT failure on emissions grounds. The system must be functioning correctly to pass.
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What Happens If AdBlue Runs Out
Warning lights appear first:
Your dashboard will warn you when AdBlue is low — typically at around 1,500 miles remaining. Ignoring warnings repeatedly can trigger a limp mode that limits engine power.
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Engine may not restart:
On some vehicles, if the AdBlue tank runs completely dry, the engine will start one final time and then refuse to restart until it is refilled. Do not ignore low AdBlue warnings.
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Top up is straightforward:
AdBlue is widely available at fuel stations, motor factors, and supermarkets. CheckFuelPrices covers thousands of UK stations where you can find diesel and check if AdBlue is sold nearby.
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Keeping Your Diesel Running Smoothly
Check your level regularly:
Top up AdBlue every service or when warned by the car — do not wait until empty. A 10-litre top-up typically costs between £10 and £20 at most fuel stations.
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Find a station near you:
Use CheckFuelPrices to locate diesel stations near you, helping you plan fuel stops where AdBlue is also available.
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Sources
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