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AdBlue®: Selective Catalytic Reduction

Advanced emissions control for diesel engines.

Many of our diesel cars are fitted with an advanced emissions control system which helps the vehicle comply with the latest Euro 6 exhaust gas regulations. The addition of AdBlue® allows for far-improved MPG returns, so this cost is more than off-set by the reduced costs in diesel.

How does it work?

AdBlue®, a water/urea based additive for diesel engines, is stored in a tank and injected directly into a specially modified part of the vehicle’s exhaust. This, in turn, begins a chemical reaction in order to remove the polluting oxides of nitrogen, converting them into harmless oxygen and nitrogen in a process called ‘Selective Catalytic Reduction (SCR)’. SCR is only available for diesel engines and you will use less AdBlue® the more economically you drive.

Depending on the model and size of the vehicle you have, the size of the AdBlue® tank fitted and the rate at which AdBlue® is consumed will vary. Many other factors will also affect how much AdBlue® is used (and, by extension, how often top-ups will be required), these include: mileage, driving style, journey type, and environmental conditions.

Generally, a passenger car can consume approximately 1 litre of AdBlue® every 600 miles, but please refer to your operator’s manual, or speak to a member of our staff for more in-depth information.

How will I know when to top AdBlue® up?

When your vehicle is due a top up, a series of warnings will be given via the driver information system. These warnings, and their frequency, will differ depending on your vehicle’s make and model, so please refer to your manual if you have any concerns.

However, if these warnings are ignored and the AdBlue® is allowed to deplete, the vehicle will no longer restart once the ignition is turned off; this is a required feature of the system, not a fault. If this happens the vehicle will require a full AdBlue® top-up and a repairer will be required to re-programme the vehicle before it can be restarted. If in doubt, please contact a member of our staff who are happy to help.

TCH Leasing will pay for AdBlue® top-ups that are within your scheduled service visits; however, it will be the driver’s responsibility to arrange the top-up outside of these scheduled service visits. AdBlue® can be purchased from most good fuel stations.

Other Important Information

  • AdBlue® is not a fuel additive. This is why it requires a separate tank

  • If you put AdBlue® in your fuel tank by mistake, do not start the engine. Instead, contact us immediately for help

  • Put only AdBlue® in the AdBlue® tank; do not fill the tank with any other liquids

  • Prevent anything from contaminating AdBlue®

  • If small quantities of AdBlue® come into contact with your skin or the vehicle’s paintwork, wipe it off immediately and rinse the area thoroughly with water

AdBlue® Errors

According to the AA, 23,000-plus breakdowns have been linked to the misuse of AdBlue in diesel cars.

What is AdBlue?


AdBlue is a liquid solution of urea that is used in diesel cars that are equipped with a Selective Catalytic Reduction system, the liquid solution is injected automatically into the flow of exhaust gas and causes a chemical reaction that converts harmful nitrogen oxides into harmless water and nitrogen, cleaning up exhaust emissions.

The solution is inserted into the car's separate filler for the AdBlue tank which is often located next to the diesel fuel filler and should not be poured directly into the fuel tank. The car's own filter will take care of injecting small quantities of the solution into the flow of the exhaust gas.

The AA is seeing a rapid growth in breakdowns due to the lack of understanding or accidental misuse of AdBlue. If the engine is allowed to run with AdBlue in the fuel tank, the damage could be very expensive.

If you run out of AdBlue your engine will likely reduce its power and performance and often drivers find that their cars won't start simply because their AdBlue tank has run dry. This can come as a shock to drivers who don't often drive a diesel car and are perhaps driving it as their fleet car or hire car and don't have a full understanding of what AdBlue does.

If you are driving a diesel fleet car, it's likely that you will need to top up the AdBlue at least once between services so it's advised that you keep an eye on the dashboard warning lights, especially if you are a high mileage driver.

The dashboard of your vehicle will always give ample warning - usually when there is a 1500 mile supply of AdBlue remaining- for when the tank needs replenishing, so make sure you don't ignore the signs and keep your AdBlue topped up correctly.

The important thing to remember about AdBlue is that it is an exhaust fluid, not a fuel additive, and is stored in a separate reservoir. If you accidentally put AdBlue into your fuel tank it could cause expensive damage to your engine so should be flushed out and refilled with diesel before the engine is started.

More Information

For more information about AdBlue® or the SCR system please contact us on 0333 240 7158 and one of our members of staff will be happy to assist you.