What Is AdBlue?
FixMyCar explains everything you need to know about AdBlue, including what it is & how it works.
Book a car repair nowEllie Dyer-Brown
Tuesday January 23 2024
8 min read
Many modern diesel cars use a fluid called AdBlue to help lower emissions. But what is it made of, and how does it work? This guide covers everything you need to know, including when and how to top it up.
What is AdBlue?
AdBlue is a brand name for diesel exhaust fluid, which is used by some cars to reduce the toxicity of exhaust gases in line with Euro 6 emissions standards. It is colourless, non-toxic, and has a subtle sweet smell. It feels sticky but is easy to wash off if you get it on your skin.
What is AdBlue made of?
AdBlue is made from a simple solution of distilled water and urea. If you think urea sounds familiar, that’s because it is - it’s found in your urine and is also used in fertilisers.
Is AdBlue made from pigs’ urine?
The rumour that AdBlue is made of pigs’ urine has gained traction in recent years. However, this is nothing more than a myth. Urea is found in urine - that part is true enough - but not the kind used in diesel exhaust fluid; it is neither pure nor sterile enough. Instead, the urea used to produce AdBlue is a man-made solution.
What does AdBlue do?
AdBlue works with a treatment system called Selective Catalytic Reduction (SCR). It is injected into a modified segment of the exhaust, where it triggers a chemical reaction that removes nitrogen-oxide emissions (NOx) by converting them into nitrogen and water.
These emissions are a waste product of the combustion process and have been linked to respiratory conditions that deteriorate people’s overall health. That’s why Euro 6 emissions standards, affecting vehicles built since September 2015, limit the amount of NOx that cars can legally emit.
A vehicle's emissions determine whether it can enter London’s Ultra Low Emission Zone; similar schemes around the country charge vehicles that produce more nitrogen oxide to enter certain areas.
Which cars use AdBlue?
Petrol cars don’t use AdBlue because NOx emissions are specific to diesel engines. And while many Euro 6 compliant diesel cars use AdBlue, not all of them do; other systems can be used instead.
You can do a few things to check whether a car uses AdBlue.
Find out whether ‘blue’ or ‘SRC’ are part of the vehicle’s name. For instance, Citroen diesels that use AdBlue are badged BlueHDi; Volkswagens are badged TDI SCR.
Check for a blue filler cap beneath the fuel flap.
Consult the vehicle handbook.
How long does AdBlue last?
One litre of AdBlue typically lasts around 600 miles. A full tank should last at least 6,000 miles but could last as many as 10,000 before needing a refill. Numerous factors, including your driving style, journey type, mileage and environmental conditions, impact this distance.
There is a common misconception that AdBlue makes your car use more fuel; however, this is not true. Check out this guide for fuel saving tips.
How to tell how much AdBlue is left in the tank
Cars that use AdBlue have a display or gauge somewhere on the dashboard (or, failing that, in the trip computer) showing how much fluid is in the system. Your vehicle handbook will tell you where to find it and what it looks like.
Like fuel and engine oil, your car will alert you with a dashboard warning light long before the AdBlue runs out.
Find out about other car warning lights and what they mean here.
Can I refill the AdBlue myself?
Some cars allow you to refill the AdBlue yourself; others don’t. Fortunately, it’s easy to find - open your fuel filler flap, and there should be a second blue cap for AdBlue beside the diesel cap. If you’re confident your car uses AdBlue but can’t find the second filler cap, you will have to get it topped up by a mechanic.
It's worth noting that AdBlue is usually topped up during an annual service. Find out what else is included in this guide.
How to refill your car’s AdBlue
Some manufacturers, including Peugeot, recommend that due to the tank's position, you should have the refill carried out by a local dealer. However, if you decide to do it yourself, park on a flat surface and ensure the engine is switched off.
AdBlue is non-toxic but corrosive and may irritate your skin if you spill it. We recommend wearing gloves while filling the tank and thoroughly washing your hands and arms after. You should also clean any spillage off your car, as it can damage the paintwork.
Step one: Check your vehicle handbook
Before you start, consult your vehicle handbook to find out where the tank and filler cap are. Read any guidance carefully to check for special instructions.
Step two: Open the filler cap
You can usually do this by hand, though some cars require a wheel brace to release the cap.
Step three: Attach the refill bottle
Screw the connector of the refill bottle on and drain the AdBlue into your car’s tank. Check the vehicle handbook to see whether the system has a minimum fluid requirement.
Step four: Close the filler cap
You can close the cap once the tank is full (or the refill bottle is drained).
How do I know when my AdBlue tank is full?
A warning will appear on your dashboard when the AdBlue system runs low. Most tanks have a capacity of around ten litres, but it’s best to consult your vehicle handbook before topping it up to find out exactly how much you need.
Once you’ve refilled the tank, the dashboard warning should disappear, confirming the fluid level is sufficient.
How to reset an AdBlue warning light
As discussed above, the dashboard warning light or message should disappear when you have topped up the tank. If this doesn’t happen, the first thing to do is try driving for a few miles, giving the system time to reset.
If the warning still doesn’t disappear or keeps coming on intermittently, there is likely a problem with the system or its sensors. Your vehicle handbook may have some practical advice for what to do in this situation - it varies between different makes and models. Failing that, the best thing to do is take your car to a mechanic who can diagnose and fix the problem.
What happens if I don’t use AdBlue?
If your car runs out of AdBlue, it will switch off or go into ‘limp mode’, drastically reducing power to keep emissions within the legal limit. Once you switch it off, it won’t start again until you refill the tank. However, there’s no need to worry because your car will give you plenty of warning before it runs out.
Volkswagen cars, for example, display a message when the range is 15,000 miles, repeated every 62 miles until the range drops to 1,000 miles. After this point, the message turns amber to show increased urgency and repeats every 31 miles. Eventually, the warning turns red before the car switches off and won’t restart.
What happens if I put AdBlue in a diesel tank?
Avoid putting AdBlue in your car’s diesel tank at all costs. Otherwise, the fuel tank will need draining and flushing clean immediately, costing you money and preventing you from using the car until it's done.
The good news is that you can’t accidentally put diesel in the AdBlue tank because the fuel nozzle is far too big.
Read this guide for advice about what to do if you put the wrong fuel in your car.
How much does AdBlue cost and where can I buy it?
Though the price varies, most motoring stores, fuel stations, and main dealers sell AdBlue. A ten-litre bottle from a motoring discount store will likely cost around £10, whereas a dealer may charge closer to £1.50 per litre.
When you purchase AdBlue (or any other brand of diesel exhaust fluid), it’s important to ensure it meets the correct specifications so it doesn’t damage your car’s SCR catalyst, which is expensive to repair. Look for the ISO 22241 number on the bottle - an international standard protecting your vehicle from contamination and damage. It may also appear as ISO 22241-3, ISO 22241-2 or ISO 22241-1.
AdBlue lasts for just a year before it starts to degrade, so there's little point in stocking up and keeping a supply for later use.
Common AdBlue problems and how to fix them
The AdBlue system can develop numerous problems, some of which are easier to fix than others.
Low fluid - This problem is easy to fix by adding more AdBlue to the system.
Nozzle failure - AdBlue is injected into the exhaust using a nozzle; if it fails, it needs replacing to keep your car’s emissions at the right level.
Sensor failure - Car sensors are prone to failure, including in the AdBlue system. The solution is to replace any faulty sensors.
Clogged SCR catalyst - A dirty SCR catalyst can lead to considerable system damage; it either needs cleaning or replacing to prevent expensive repairs.
If you’re experiencing issues with your car’s AdBlue system, FixMyCar can help you find the best price for a reliable repair.
If you found this guide helpful, you might also like:
- Related topics:
- Ad Blue
- Car Ownership
- Maintenance
- Servicing And Mot
