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What is AdBlue?

  • The generic term is Diesel Exhaust Fluid (DEF)
  • Injected into the exhaust system, it will be used at a rate of around 5 litres per 100 litres of diesel
  • It reduces diesel exhaust nitrogen oxide emissions by more than 90%
  • Officially AdBlue is the registered trademark for Aqueous Urea Solution 32.5%, used with the Selective Catalytic Reduction system (SCR)



ADBLUE is a fluid treatment used to clean up diesel exhaust emissions and while it first appeared for trucks it is becoming increasingly used for premium cars too – so you need  to be aware of it so that you can advise customers.

It is not just another blue fluid to keep checking in cars or vans, alongside the antifreeze and screenwash – and it must not be taken for granted.

AdBlue is a key to the less polluting Euro 6 emission regulations, enabling diesels to retain access to city centres. The fluid is injected into the exhaust system just ahead of a catalytic converter.

Run low on AdBlue – or worse, run out – and the vehicle goes into reduced power ‘limp’ mode. But unlike some other checks, such as tyre pressures or tyre tread depth, at least the driver gets dashboard alerts.

If the diesel car is Euro 6 compliant, which all new cars must now be, the designation helps keep down the company car tax.

Most major manufacturers have chosen the AdBlue route for compliance and this is an essential fluid used with a Selective Catalytic Reduction (SCR) system to reduce the exhaust emissions. The system has its own tank and its own filler, usually beside the diesel fuel filler.

Basically, what it does is convert more than 90% of harmful nitrogen oxide emissions into harmless nitrogen and steam and reducing these nitrogen oxides should lead to less pollution and smog in urban areas.

It’s not the only emission control feature and will often work in conjunction with a diesel particulate filter (DPF) that collects soot particles.

Originally just seen in commercial vehicles, with diesel emissions targets becoming more stringent the AdBlue injection systems have now become a feature of modern diesel-powered cars and vans.

Here are six important facts about AdBlue:

1. Will I need to top up AdBlue tank between services?

The AdBlue tank will be refilled at every service, but the size of the tank will vary whatever vehicle you choose – therefore top-ups between services might be necessary, as indicated by dashboard warnings.

Other factors such as the mileage covered, journey types, driving style and environmental conditions will have an affect on how AdBlue is consumed by a Euro 6 diesel engine.

2. How do I find and fill the AdBlue tank?

Check the owner’s manual for the location of the AdBlue tank, although it is most likely to be located next to the fuel tank or under the rear floor in a car, with filler near the fuel filler, although the filler can be in the engine bay on a van.

AdBlue is very easy to use and is not a fuel or fuel additive, but a high purity urea solution. AdBlue is non flammable, and non-explosive, and considered a transportable fluid.

3. AdBlue needs to be handled with care

If handling AdBlue, wear suitable protective clothing such as rubber gloves and glasses.

AdBlue damages surfaces such as painted vehicle parts, plastic, items of clothing and carpets and should be removed as quickly as possible using a damp cloth and plenty of cold water. Any spillage can make a floor slippery and cause staining.

If AdBlue comes into contact with eyes and skin, rinse for at least 15 minutes with plenty of water and seek medical help.

If AdBlue is swallowed, wash the mouth with plenty of water for at least 15 minutes. Do not try to induce vomiting unless recommended by a doctor. Seek medical advice immediately.

AdBlue damages surfaces such as painted vehicle parts, plastic, items of clothing and carpets and should be removed as quickly as possible using a damp cloth and plenty of cold water. Any spillage can make a floor slippery and cause staining.

4. Where can I get AdBlue from?

You’ll be able to buy AdBlue from the dealer you bought the vehicle from, or online from sites like Amazon.

AdBlue is also sold sometimes at the pump, but these are usually only for commercial vehicles, as the nozzle and fast delivery won’t be suitable for refuelling vans and cars.

5. Can I keep spare AdBlue in my vehicle?

No, it requires specialist storage. It must be kept away from direct sunlight and must be protected from temperatures which are too warm or too cold. In typical UK weather conditions, the average shelf life of AdBlue is 6-12 months, but in perfect storage conditions, this can be extended to 18 months.

6. What will happen if I don’t refill the AdBlue tank of my vehicle?

If you don’t replenish your tank with AdBlue, as prompted by dashboard warnings, eventually your vehicle simply won’t start.

However before that, running the SCR system low can result in a deliberately induced reduction in power and speed.

Finally, come MoT time in the future, your vehicle will fail, as it won’t be able to maintain the low emissions.

If it’s one filler to far…

If this all sounds a bit much, bear in mind that before long you’ll need this technology to drive a diesel into London and some other city centres with ultra low emission zones (ULEZ).

To read more about the Euro 6 regulations made mandatory for new cars and vans this year, click here.

With London’s Ultra Low Emission Zone plans for 2020, diesel Euro 6 compliance will be essential to avoid a £12.50 daily surcharge. And low emissions are critical to your tax rates too.

And if you want to consider alternative options for motoring, have a look at Breathe easy and save: Top 10 low emission cars.


AdBlue injection

Graphic showing how the AdBlue injection –splits nitrogen oxide into nitrogen and water.