Tips and advice

What is AdBlue?

If you own a diesel car built after September 2015, the chances are it’ll need AdBlue at some point. Our guide explains all

What is adblue?

You may not have heard of Adblue, also known as diesel exhaust fluid, but owners of diesel cars with Euro 6-compliant engines will have heard of it. This guide explains what Adblue is used for, how it works, where to buy it and what will happen if your car runs out.

AdBlue is a fluid which is automatically sprayed into a car’s exhaust system to reduce the nitrous oxide emissions of diesel engines. AdBlue is made of a mixture of urea and deionised water. The widespread usage of AdBlue in modern diesel cars coincided with stricter Euro 6 emissions standards that have been in effect since 2016. AdBlue makes it much easier to lower the emissions of diesel cars so they comply with these regulations.

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AdBlue is usually checked and topped up if necessary during a normal service, but it’s a good idea to check it and top it up between these intervals. Almost all cars that use AdBlue are fitted with a gauge on the dashboard to warn you if you’re running low. You can buy AdBlue from major retailers such as Halfords.

What is AdBlue used for and why do we need it?

What is adblue

Car makers have to abide by a huge number of rules, a major amount of which aim to address environmental concerns. The most recent set of emissions regulations, known as Euro 6, represented a particularly big challenge for diesel engines. One of the main goals is to minimise nitrogen-oxide emissions.

The technology is known as selective catalytic reduction, or SCR. Despite only recently becoming widely used in diesel cars, it’s existed for decades. The process involves injecting precise amounts of a liquid into the exhaust system and neutralising the harmful emissions by way of a chemical reaction.

How does AdBlue work?

To comply with Euro 6 regulations, many new diesel-powered cars built since 2016 use SCR technology to inject tiny quantities of AdBlue into the car’s exhaust gases. When this solution combines with exhaust emissions, it breaks down the harmful mono-nitrogen oxides in diesel exhaust. This technology has been used in buses and heavy lorries for a long time, so its effectiveness has been proven and its reliability is better than ever.

Does AdBlue affect fuel consumption?

Manufacturers have yet to release any data to suggest that Adblue has an adverse effect on fuel consumption. Economy figures for a new diesel car on sale in the UK will factor in any effect from the use of AdBlue in any case.

Developments in engine technology, changes to the way economy figures are calculated and a range of other variables means it’s essentially impossible to find differences in fuel consumption between new and older cars and attribute them solely to the use of AdBlue.

What is AdBlue made of?

AdBlue is a non-toxic liquid that’s colourless in appearance and is essentially a solution of water and urea – a substance found in urine. However, in AdBlue, the urea is exceptionally pure and is of a higher grade than that used in cosmetics, glue or fertilisers. Similarly, the water is demineralised, which is far cleaner than water from the tap.

When buying AdBlue, you should check it meets the correct specification, so look for the ISO 22241 number on the packaging. This may also appear as ISO-22241-1, ISO-22241-2, ISO-22241-3. This will ensure the AdBlue doesn’t damage your car’s SCR catalyst – a costly repair. Assuming your AdBlue meets these specifications, one brand of AdBlue should be pretty much the same as another, in the same way that diesel fuel is fundamentally the same from one retailer to another.

Where to buy AdBlue

Your AdBlue levels should be checked and topped up at every service and your dealer will happily refill it at other times when required but this is rarely the cheapest option. AdBlue is also sold in bottles at fuel stations and you can also order it online.

Buy Adblue refills from Amazon here.

Can I refill AdBlue myself?

Adblue refill

On several mainstream diesel models, the AdBlue filler is located behind the car’s fuel filler cap. It’s usually smaller than the main fuel filler, and will feature a blue cap and markings confirming it should only be used for AdBlue.

If you’re unsure of how to top up your car’s AdBlue, you should refer to the owner’s manual for instructions on how to access the tank - it shouldn’t be difficult. It’s also a good idea to ask the salesman to show you how to refill the AdBlue during the handover of a new car.

Where can I find an AdBlue pump?

Another option for topping up your AdBlue tank is to use an AdBlue pump. These can be found at most big filling stations in the HGV lanes. Some of the pumps feature a specific fuelling nozzle for HGVs and a different one for cars.

An AdBlue pump is usually used by truckers and is often far cheaper and less messy than trying to top-up your tank from a plastic bottle. The filling stations with AdBlue pumps were originally largely restricted to key routes and motorways but more have been added in recent years.

I have an AdBlue warning light? What should I do?

AdBlue warning

AdBlue warning display

All diesel cars that use AdBlue will give you plenty of warning if you're running low. You’ll usually be alerted with a dashboard warning at around 1,500 miles from running out, along with an amber warning light. This warning will remain on every time you restart your car until the AdBlue levels have been topped up to the desired level.

What happens if you run out of AdBlue?

Ignoring the AdBlue warning light on your dashboard is not advised under any circumstances. If you run out of AdBlue while driving, your car’s performance will likely be affected as it tries to reduce its emissions output by going into ‘limp mode,’ reducing the speed at which you can drive and sometimes turning off your vehicle’s stereo or air conditioning to preserve power.

Once you’ve stopped, the majority of modern cars cannot be restarted while the AdBlue tank is completely empty. Fortunately, this situation is easily avoidable, as AdBlue refills are straightforward and usually relatively cheap if you shop around and do them yourself.

For more information about the current road tax rules, read our in-depth guide.

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