Avoiding AdBlue Issues in Your Fleet:

What You Need to Know

AdBlue

AdBlue problems are one of the most common causes of avoidable breakdowns in modern diesel vehicles — particularly in fleets. From non-start issues to costly SCR (Selective Catalytic Reduction) system repairs, most problems stem from low fluid levels, poor quality AdBlue, or simple driver error.

The good news? Most of these issues are easy to avoid with a few practical steps.

What Is AdBlue?

AdBlue is a clear, non-toxic fluid made from high-purity urea and deionised water. It’s used in modern diesel vehicles equipped with Selective Catalytic Reduction (SCR) systems to reduce harmful nitrogen oxide (NOx) emissions.

When injected into the exhaust system, AdBlue reacts with the exhaust gases and breaks down NOx into harmless nitrogen and water vapour. It’s essential for vehicles to remain compliant with Euro 6 emissions standards — and for keeping your fleet on the road.

5 Ways to Avoid AdBlue Problems in Your Fleet

1. Keep AdBlue Topped Up – Don’t Wait for the Warning Light

Many vehicles give limited warning before going into “limp mode” or refusing to start altogether. Drivers should top up AdBlue proactively — ideally as part of their weekly vehicle checks.

Top tip: Treat AdBlue the same as fuel. Don’t wait until it’s critical.

2. Use High-Quality, ISO 22241-Compliant AdBlue

Not all AdBlue is created equal. Low-grade or contaminated fluid can damage the SCR system and lead to costly repairs. Always use ISO-certified AdBlue, whether buying in bulk or in bottles.

Avoid topping up from unlabelled containers or those that may have been used for other fluids.

3. Educate Drivers on AdBlue Basics

Many drivers either don’t understand what AdBlue is or underestimate its importance. A simple one-page guide or short briefing can go a long way in preventing issues.

Make sure drivers know:

Where the AdBlue filler cap is located.
What to do if the low AdBlue warning appears.
Never to confuse it with fuel, coolant, or oil.

4. Store AdBlue Properly

If you're storing AdBlue on-site, ensure it's kept in clean, sealed containers at a stable temperature — ideally between -6°C and +25°C. Exposure to extreme heat, cold or contamination can degrade the fluid.

Never store AdBlue in reused fuel containers or leave it in direct sunlight.

5. Take Warning Lights Seriously

Once a low AdBlue warning appears, some vehicles may only allow a limited number of miles before performance is restricted or the vehicle refuses to restart after switching off.

It’s not just a warning — it’s a countdown. Act fast to avoid downtime.

Questions and Answers about AdBlue

AdBlue is a non-toxic, colourless, and biodegradable liquid. Despite its name, it's not actually blue! It's an aqueous urea solution, composed of de-ionised water and high-purity urea.

Its primary purpose is to reduce harmful nitrogen oxide (NOx) emissions produced by diesel engines. NOx gases are a major component of air pollution and are linked to various respiratory diseases.

AdBlue works in conjunction with a technology called Selective Catalytic Reduction (SCR). Here's a simplified breakdown:

Injection: AdBlue is automatically injected in small, precise amounts into your vehicle's exhaust system, upstream of the SCR catalyst.

Chemical Reaction: Inside the SCR catalyst, the AdBlue converts the harmful NOx gases into harmless nitrogen and water vapour.

Cleaner Exhaust: The result is significantly reduced harmful emissions being released from your tailpipe, allowing your vehicle to comply with the Euro 6 emission regulations – a legal requirement for most modern diesel vehicles registered from September 2015 onwards.

AdBlue consumption varies depending on your vehicle's make and model, engine size, driving style, and even the outside temperature. As a general guide, many vehicles consume around 1 to 1.5 litres of AdBlue every 600-1000 miles.

Your car will give you ample warning when your AdBlue level is running low, typically via a dashboard warning light or message. Don't ignore these warnings!

What Happens if I Run Out of AdBlue?

If your AdBlue tank runs dry, your vehicle's engine management system will take action to ensure compliance with emissions regulations. This usually means:

Reduced Performance (Limp Mode): Your car may enter a "limp home" mode, significantly reducing engine power and performance to limit emissions.

Engine Won't Restart: Critically, if you completely run out of AdBlue and turn off your engine, it will not restart until you've refilled the AdBlue tank. This is a legal requirement to prevent the vehicle from being driven without the emissions control system functioning.

Potential Fines: Driving a vehicle that is not compliant with emissions standards could lead to fines.

AdBlue is widely available in the UK:

Petrol Stations: Many fuel stations offer AdBlue in pre-filled containers or at dedicated AdBlue pumps (more common for HGVs, but some car-friendly pumps exist).

Automotive Retailers: Stores like Halfords and other car parts shops stock various sizes of AdBlue containers.

Supermarkets: Some larger supermarkets also carry AdBlue.

Online Retailers: You can buy AdBlue in bulk or smaller quantities from various online suppliers.
Dealerships/Garages: Your car dealership or local garage can top up your AdBlue as part of a service or as a standalone service.

When buying ADBlue make sure you buy a good quality product that is certified - ISO 22241

While AdBlue is generally reliable, some common issues can arise:

Crystallisation: If AdBlue is exposed to air or extreme temperatures, the water can evaporate, leaving behind solid urea crystals. This can clog the injector, pipes, and filter. Short, frequent journeys where the system doesn't reach optimal temperature can exacerbate this.

Sensor Failures: The system relies on sensors to monitor levels and functionality. These can sometimes fail, leading to incorrect warning lights.

Pump or Injector Issues: Like any mechanical part, the AdBlue pump or injector can develop faults or blockages.

Contamination: Using low-quality, expired, or contaminated AdBlue (e.g., mixed with fuel, dirt, or water) can severely damage the SCR system.

Tank Heater Failure: AdBlue freezes at around -11°C. Modern vehicles have heaters to prevent this, but these heaters can fail in very cold weather.

Need Help Managing AdBlue in Your Fleet?

If you’d like a simple driver checklist or advice on the best way to manage AdBlue refills across your fleet, our team can help. Whether you're running 1 vehicle or 200, a proactive approach will save you time, money and hassle.

Need some help managing you vehicle fleet. Find out how MPH can support you.

Head to our contact page.