Expert advice: what is AdBlue and why it’s vital for some diesels


Run out of AdBlue and you might struggle to get going again

AdBlue is becoming an important part of our motoring life. And for drivers of diesel cars it could make the difference between miles of trouble-free, low pollution motoring and their car not working at all.

There are currently estimated to be more than 200,000 vehicles using AdBlue in Europe. This is because it’s been popular in the haulage industry for the past 20 years as a means of reducing poisonous exhaust emissions.

Although AdBlue is neither a fuel nor a fuel additive, cars that use it can stop running if they don’t have a sufficient amount in a special on-board tank. That’s because the AdBlue is designed to be injected into the exhaust fumes and remove the harmful nitrogen oxide gases. The trouble is, some drivers aren’t sure what AdBlue is and ignore the car’s reminders to fill it up. Sometimes when the AdBlue tank runs dry the car won’t start and they then have to call us out to get going again. Here’s all you need to know about AdBlue.

How do you know if your car uses AdBlue?

For a start, only diesel cars use AdBlue. And because the technology is complex and therefore expensive, it tends to be reserved for larger models. In Volkswagen’s case, that’s the Passat, Tiguan, Touran and Touareg. The PSA Group of Peugeot, Citroen and DS cars are an exception. Any of its models with a BlueHDi engine will feature AdBlue. If you’re unsure whether your car uses the technology, check the car’s user manual.

How do you know if the AdBlue needs topping up?

AdBlue tanks are between 10 and 20 litres and it’s estimated 1.5 litres will let you cover 620 miles. That means they will need filling up every 6000 miles or so. Cars will flash up warnings increasingly as the tank empties. The trouble is, a lot of drivers don’t know what the warnings mean and don’t realise how crucial it is to top the tank up.

What if you run out of AdBlue

If a car runs low on AdBlue, the engine may stop working and that means a breakdown. Rather than conking out roadside, it will refuse to start, telling you to get the emissions system seen to.

Find out all about your car’s Diesel Particulate Filter

Is filling with AdBlue an easy job to do?

It depends on the car you’re running. The German cars have a blue filler cap next to the diesel one behind the fuel filler flap. To replenish these cars you go to your motor retailer or local filling station and buy bottles of AdBlue. A four-litre container costs £12. Included in the box is a special spout that enables you to fill the tank without fiddling about and spilling your precious liquid. On other cars, it’s not as convenient. Some VW Group models have the tank in the boot. With PSA Group cars, you need to take the car to the dealership for the job to be done by a technician.


On many modern cars the AdBlue filler is next to the diesel

What is AdBlue?

This is a mixture of water and the chemical compound urea. It’s in a tank and is injected into part of the exhaust system sometimes known as a Selective Catalytic Reduction Catalyst. Hence the process is known as Selective Catalytic Reduction (SCR). There it begins a chemical reaction with the nitrogen oxides (NOx) in the exhaust gases. This converts the harmful NOx gases into harmless nitrogen and water.

Why is it called AdBlue?

AdBlue is a trademark. Although AdBlue is supplied by various companies, it all has to comply with the same standard if it’s to wear the AdBlue trademark. You could probably find a solution that claims to be water and urea elsewhere but using anything other than AdBlue would invalidate any warranty your car might have.

self-driving carsNick Reid is head of automotive technology for Green Flag and is a fellow of the Institute of the Motor Industry

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