What happens if you run out of AdBlue? Might not be as bad as you think!

(Last Updated On: May 30, 2023)

It may be your first time owning a diesel vehicle with an AdBlue system. The blue light may surprise you with a countdown timer. But what happens if you run out of AdBlue? 

A valid question that it is best to avoid experimenting with.

Instead, let’s keep you out of harm’s way and save you some unnecessary costs. Running out of AdBlue is bad – simple and clear. 

Let’s cut to the chase. 

Running out of AdBlue will not destroy your engine or cause any damage to the engine and its components. Although, vehicle restrictions could put you and the car’s occupants in harm’s way. 

What is AdBlue?

Adblue is a synthetic carbamide solution(chemical urea) diluted with pure de-ironized water. It has many names, such as Diesel exhaust fluid or DE Fluid for short but known as AdBlue. 

I’m sure you’ve heard the story that people believe AdBlue is pigs’ urine. But, it is not valid. Chemical urea is in pig urine which is where people make the connection. But, it’s found in a much lower quantity than the amount produced for AdBlue. 

What does AdBlue do? 

The job of AdBlue is simple; it is to reduce vehicle emissions. Many vehicles after 2015 have a Selective Catalytic Reduction (SCR) system. The SCR uses AdBlue, which is injected into the exhaust gases in minimal quantities. The AdBlue injected into the exhaust gases passes through the SCR. A chemical reaction converts harmful exhaust gases into nitrogen and water. 

This reduces diesel vehicle emissions and makes for a much cleaner exhaust system. AdBlue is now an essential part of modern diesel engines. The addition of AdBlue allows modern diesel vehicles to meet lower emission regulations. 

AdBlue has been used in trucks and buses since 2006 with the introduction of Euro4 emissions. Yet it is still very new to cars, SUVs, and 4x4s. 

What happens if you run out of AdBlue?

In most vehicles, the car will run down and fail to start the next time you turn off the vehicle until you refill the DE fluid. The good news is it will cause zero engine damage. The car’s emissions will be wrong when driving without DE fluid, which would be illegal, so the manufacturers remove the choice of driving illegally from you. However, some vehicles have a more sinister approach to running out of AdBlue.

If you dare to run the AdBlue system down to 0 miles, the car will go into a limp home mode(limp mode). Limp mode is an engine protection mode pre-programmed into the vehicle. It’s designed to stop you from causing damage to the car by driving when there is a fault. The vehicle will struggle to speed up past 30mph and hold back under acceleration. 

Limp home mode

The limp home mode can be dangerous if traveling at speeds on fast roads in heavy traffic. There may not be other warnings, only the AdBlue light. Don’t panic yet! 

Your vehicle will warn you that the AdBlue tank needs refilling with plenty of time. The light will illuminate when there are around 1500 miles (2414 km) left(each car differs). 

When you run out of AdBlue and enter limp mode, the vehicle will not switch back on after switching off. The car will restart once the AdBlue is refilled. Some vehicles require the car ignition to be switched on to allow calibration before starting, your cars handbook will confirm the process. There is also a risk that your car may only give you so many miles (k/m) before it shuts itself off. 

How long does AdBlue last?

Depending on each car, AdBlue will last 3 – 10,000 miles in most vehicles. Some have smaller AdBlue tanks than others, so refilling can become regular. 

Most vehicles use around 1 liter (0.22 gallon) per 500 – 600 miles (804 – 965km) in normal driving conditions. 

AdBlue does have an expiration date and can be stored un-open for around 12 – 18 months. After some time, the AdBlue loses its strength and renders itself useless. Have a read here to find out more on AdBlue expiration.

This shouldn’t concern most, but AdBlue also freezes at -11 degrees celsius or 12 degrees Fahrenheit; while it’s in the car that’s not too much of an issue because the vehicle has it’s AdBlue heater. While storing in a bottle, the bottles can crack as the AdBlue expands when it freezes.

Where can you buy AdBlue? 

AdBlue is available at most fuel station forecourts, hardware, grocery stores, and online. AdBlue is usually supplied in 5l and 10l bottles. Your vehicle handbook will tell you the size of the DE fluid tank fitted to your vehicle. 

Because AdBlue doesn’t store very well once opened, only buy what you need. Opened AdBlue exposes itself to air which will cause it to lose its strength, so it doesn’t keep for a long time. AdBlue bottles are recyclable. But unfortunately, the excess fluid must be disposed of unless you can find someone else who can use it immediately. 

adblue filler cap

Where does AdBlue go? 

All diesel vehicles using AdBlue will have a separate AdBlue tank and filler cap. Usually, the AdBlue tank is situated next to the diesel filler cap or in the car’s trunk. Once an AdBlue tank is filled, the AdBlue trip will reset and reconfigure itself. 

AdBlue must not be poured directly into the diesel tank or vice-versa.

AdBlue mixed in the diesel tank will cause damage to fuel injectors, fuel pumps, and filters. If you make this mistake, DO NOT start the vehicle or even try to drive it a few meters. The damage will already have set in. 

Instead, call your roadside recovery, who will be able to aid in draining and cleaning the fuel tank. The removed diesel will need to be disposed of, but the repair cost would be much higher. The risk of driving contaminated fuel is not worth the repair bill. 

Final say

AdBlue is a legal requirement to diesel cars with an SCR system, so there is no workaround to not using it. 

The dangers of driving when you run out of AdBlue should be enough to put you off ever running the risk. Unfortunately, tens of thousands of drivers every year do make this mistake. They are lucky enough that they get to find out first-hand what happens if you run out of AdBlue. As soon as you see the Diesel Exhaust Fluid light illuminate on the dashboard, don’t put off refilling with AdBlue. The quicker you get it done, the quicker you can forget about it.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.