What Is AdBlue? A Simple Guide for UK Diesel Drivers

Summary

• AdBlue reduces emissions: It's used in diesel cars with SCR systems to cut harmful NOx gases by up to 90%.
• You need to top it up: Most diesel cars use 1-2 litres of AdBlue per 600 miles.
• Don't ignore the warning light: Your car won't start if the AdBlue tank runs dry.

If you drive a modern diesel car, you've probably seen the AdBlue warning light. But what is AdBlue? And what happens if you run out?

This guide answers all your questions in plain English. No mechanic jargon. Just the facts you need.

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What Is AdBlue?

AdBlue is a clear liquid made from urea and water. It's not a fuel additive. You don't mix it with diesel.

Your car has a separate AdBlue tank. The fluid is sprayed into the exhaust system. There, it breaks down harmful NOx (nitrogen oxide) gases into harmless nitrogen and water.

This system is called SCR — Selective Catalytic Reduction. Most diesel cars made after 2015 have it.

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Which Cars Use AdBlue?

Most Euro 6 diesel cars use AdBlue. This includes cars made after September 2015.

Common brands that use AdBlue include:

• Audi
• BMW
• Mercedes-Benz
• Volkswagen
• Ford (some models)
• Peugeot
• Citroën
• Jaguar Land Rover

Not sure if your car uses AdBlue? Check your owner's manual. Or look for a separate blue filler cap near your diesel cap.

You can also run a car history check to see your car's full specifications.

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How Much Does AdBlue Cost?

AdBlue is cheap. A 10-litre bottle costs around £10-£15 from most car parts shops.

You can buy it at supermarkets, petrol stations, Halfords, or online. Some larger petrol stations even have AdBlue pumps.

Where to Buy	Typical Price (10L)
Supermarket	£8 - £12
Halfords	£10 - £15
Petrol station pump	£0.50 - £1.00 per litre
Online	£8 - £14

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How to Top Up AdBlue

Topping up AdBlue is easy. You can do it yourself in a few minutes.

1. Find the AdBlue filler cap. It's usually next to the diesel cap or in the boot.
2. Open the cap and insert the bottle nozzle.
3. Pour slowly to avoid spills. AdBlue can stain paintwork.
4. Replace the cap firmly.
5. Start the engine. The warning light should clear within a few miles.

Warning: Never pour AdBlue into your diesel tank. And never pour diesel into your AdBlue tank. Both mistakes can cause serious damage costing thousands to fix.

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How Often Do You Need to Top Up?

Most cars use about 1-2 litres of AdBlue per 600 miles. A typical tank holds 10-20 litres.

This means you might need to top up every 5,000 to 10,000 miles. Some drivers only need to do it once or twice a year.

Your car will warn you when AdBlue is getting low. You'll usually get a dashboard warning at around 1,500 miles before it runs out.

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What Happens If You Run Out?

This is important. If your AdBlue tank runs dry, your car will not restart after you turn it off.

The car will still run while the engine is on. But once you switch off, it won't start again until you top up the AdBlue.

This is by law. EU and UK regulations require the car to prevent operation without a working emissions system.

Don't ignore the warning light. Top up as soon as you can.

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Common AdBlue Problems

Sometimes the warning light stays on even after topping up. Here's what might be going on:

• Sensor fault: The level sensor can fail. A garage can reset or replace it.
• Poor quality AdBlue: Always buy ISO 22241 certified AdBlue. Cheap alternatives can damage the system.
• Frozen AdBlue: AdBlue freezes at -11°C. Your car has a heater to thaw it, but very cold weather can cause temporary issues.
• SCR system fault: If the catalytic reduction system fails, the light stays on. This needs a professional repair.

If you're having problems, your car may flag issues during the MOT test. Emissions are checked as part of the MOT.

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AdBlue is simple, cheap, and essential for modern diesel cars. Keep an eye on your dashboard warning, top up regularly, and you'll have no problems. It's a small task that keeps your car legal and your emissions down.

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