AdBlue & DPF
Using AdBlue
How does AdBlue work?
CheckFuelPrices Editorial
Expert Written • 4 industry sources
AdBlue is a liquid solution injected into a diesel exhaust system to convert toxic nitrogen oxide (NOx) emissions into harmless nitrogen and water vapour. It is used in a system called Selective Catalytic Reduction (SCR), fitted to most diesel cars and vans built after 2015.
The Science Behind AdBlue
What AdBlue is made of:
AdBlue is a precisely mixed solution of 32.5% high-purity urea and 67.5% deionised water. It is non-toxic, non-flammable, and non-hazardous to handle.
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How SCR converts NOx:
When AdBlue is injected into the hot exhaust gases, the heat causes it to release ammonia. Inside the SCR catalyst, the ammonia reacts with NOx to produce only nitrogen and water vapour — both harmless.
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Why diesel engines need it:
Diesel combustion produces high levels of NOx, which is a harmful air pollutant linked to respiratory problems. SCR with AdBlue is the most effective technology available to reduce these emissions.
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Which Vehicles Use AdBlue?
Euro 6 diesel cars and vans:
AdBlue is standard on most diesel cars and light vans built to meet Euro 6 emission standards, introduced in September 2015. If your diesel was registered after this date, it likely has an SCR system.
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Separate filler cap:
AdBlue is stored in its own tank with a separate filler cap — usually found near the fuel cap, in the boot, or under the bonnet. It must never be mixed with diesel.
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Not fitted to all diesels:
Some older or smaller diesel engines use alternative emission control methods such as exhaust gas recirculation (EGR) without SCR, and do not require AdBlue.
Running Out of AdBlue
Warning light comes on first:
Your dashboard will warn you when AdBlue is running low — typically when around 1,500 miles of range remains. Do not ignore this warning.
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Engine may not restart:
If AdBlue runs completely dry, many vehicles are programmed not to restart once the ignition is switched off. This is a manufacturer-enforced measure to ensure emissions compliance.
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Consumption rate:
A typical diesel car uses roughly 1 litre of AdBlue per 600–1,000 miles, though this varies by engine size, driving style, and load.
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Topping Up AdBlue
Available at most filling stations:
AdBlue is widely sold at petrol stations, motor factors, and online. It is usually available in 5-litre or 10-litre containers, or via a pump at larger forecourts.
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Use the correct grade:
Always use AdBlue that meets the ISO 22241 standard. Using the wrong fluid or contaminating the tank can cause serious and expensive SCR system damage.
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Sources
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