AdBlue in a van: what it's for and what happens if it runs out

What AdBlue in a van is

AdBlue in a van is an operating fluid that reduces the amount of nitrogen oxides in the exhaust gases. It's neither fuel nor a diesel additive. It has its own tank with its own filler neck, usually with a blue cap next to the diesel filler or under the bonnet.

How it works

It's an aqueous urea solution. The system injects it into the exhaust pipe ahead of the catalytic converter. There it breaks down and turns harmful nitrogen oxides into nitrogen and water vapour. This system is called SCR and you'll find it on practically all newer diesel engines.

It has no effect on engine performance. As long as there's enough fluid, the system runs in the background and you don't even know it's there. It's not something you have to operate while driving.

Without AdBlue the vehicle wouldn't meet the emissions standard. That's why manufacturers monitor the system, and the control unit can tell when the fluid runs out or when someone tops up with something else.

How much is used

Consumption is in the order of a few per cent of diesel consumption. Put simply: a full tank of diesel needs only a small amount of AdBlue. But it rises with load, so a loaded van in the hills uses more than an empty one on the flat.

For a normal rental you usually don't need to do anything. The supply in the tank lasts hundreds to thousands of kilometres and the vans are topped up during servicing. On a house move around Prague or a weekend materials run, you won't get anywhere near the limit.

On longer trips it's worth keeping in mind. Mileage within the Czech Republic is unlimited with us, so if you're planning a drive across the whole country, take a look at the messages on the dashboard right at the start of the rental.

How you can tell it's running low

The van warns you well in advance. A message appears on the dashboard showing how many kilometres are left. At first it's for information only; later it turns into a warning and the countdown becomes more precise.

Some vans also have a level gauge. You'll find it in the on-board menu next to the consumption and range figures. It's not standard on all models, but it's worth looking for.

Don't confuse it with the fuel warning light. The AdBlue message is usually text or has its own symbol and has nothing to do with the fuel gauge. Our vans run on diesel, which you fill up in the normal way under the full-tank rule at pick-up and return.

What happens if AdBlue runs out

First, reduced power

The system can't be switched off or bypassed. When the level drops below the minimum, the vehicle starts limiting its power. The engine keeps running, but acceleration is noticeably more sluggish and the speed may be limited.

Then the van won't start

The most serious thing is the start lock. Once the supply is completely used up, the van will get you to where you're going, but after you switch off the engine it won't start again until you top up the fluid. That's why it doesn't pay to ignore the message, even if it still shows hundreds of kilometres.

After topping up it takes a moment. The system needs to detect the fluid, which can mean a few minutes with the ignition on or a short drive before the message disappears.

How to top up

Only buy fluid intended for SCR. It's sold at petrol stations and car parts shops, usually in canisters with a funnel or in packs with a hose. Never pour water, diesel or anything else into the tank — damage to the system is expensive.

Use the right filler neck. The blue cap is for AdBlue, the black or grey one for diesel. Mixing them up means a tow and a system flush, so be careful at the pump even when you're in a hurry.

Top up carefully. The fluid is colourless but leaves white stains on paintwork and clothing. If any drips, rinse it off with water.

Storage and frost

AdBlue freezes at around minus eleven degrees. In the vehicle it doesn't matter, as the tank is heated. But a canister in the garage can freeze over the winter. Once thawed it's still usable; it just mustn't be warmed up with anything hot.

An opened pack ages. Don't buy a supply for years ahead — the fluid has a limited shelf life and doesn't like standing in direct sunlight for long.

Carry the canister upright. The cap isn't completely leak-proof if tipped over, and fluid spilled in the load space leaves stains on everything you're carrying.

If you're not sure what to do

Get in touch with us. We operate around the clock, so if a message you don't understand appears during the rental, we'll advise you over the phone. We've also described the basic situations in the FAQ, and you'll find an overview of the vans in our fleet.