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How AdBlue works

AdBlue is a precisely formulated solution of 32.5% urea in deionised water. It is injected into the exhaust pipe upstream of the SCR catalyst, where the heat of the exhaust gas breaks it down into ammonia. The ammonia then reacts with NOx over the catalyst surface, converting it to harmless nitrogen gas and water vapour. The reaction reduces NOx emissions by up to 90%, which is why SCR systems are essential for meeting Euro 6 limits.

AdBlue is not a fuel additive and must never be added to the diesel fuel tank. It is stored in a separate tank, usually with a blue filler cap, and is consumed in proportion to fuel used — typically around 1 litre of AdBlue per 600–900 miles of driving.

Top-up intervals and low-level warnings

Most vehicles provide a dashboard warning when the AdBlue level reaches around 1,500 miles remaining. Ignoring the warning will lead to a second warning at approximately 500 miles, followed by a restricted performance or start-inhibit mode when the tank is empty. Refilling before the tank is completely empty is strongly recommended.

AdBlue degrades over time and should not be stored for more than 12 months once opened. Always use ISO 22241-compliant fluid — substandard products can damage the SCR catalyst and injector.

• Only add AdBlue to the dedicated AdBlue filler (blue cap)
• Never add AdBlue to the diesel tank
• Use ISO 22241-compliant fluid only
• Refill before the tank runs dry to avoid start-inhibit
• Store in a cool location, use within 12 months of opening

Buying AdBlue

AdBlue is available in containers from 1.89 litres to 10 litres and in IBC totes for commercial use. Compare prices on this page for the quantity you need. Free UK delivery on orders over £99.