How to Clean & Maintain Your Diesel SCR (Selective Catalyst Reduction) System

Do you know if your diesel vehicle has an Selective Catalyst Reduction (SCR) system?

Do you know what it does? Do you know why it’s there?

Many diesel owners don’t give their SCR systems a second thought until problems and repair costs rear their heads. Then everyone starts wondering why there isn’t a better way to maintain the SCR system so that problems don’t occur in the first place.

Well, we can help.

What is an SCR system in a diesel vehicle, anyway?

Here’s the basic explanation:

An SCR (Selective Catalytic Reduction) system in diesel vehicles helps to make the exhaust “cleaner”. It’s not part of the engine; it’s an exhaust gas after-treatment component of the DEF (Diesel Exhaust Fluid) and emissions systems.

In the US, the EPA introduced new diesel engine emissions standards for heavy-duty commercial vehicles back in 2010, which led to the widespread adoption of SCR technology. In Europe, the Euro 6 standard, which tightened the guidelines on polluting emissions from diesel engines, made it mandatory for all diesel vehicles from 2015 onwards to be equipped with an SCR system.

So, if you have even a moderately recent diesel vehicle, you have an SCR.

The SCR works by using a special urea liquid called DEF (Diesel Exhaust Fluid) to clean the exhaust. (DEF is mainly a North American name, AdBlue™ is more common elsewhere in the world.) An SCR system needs the DEF liquid to be refilled from time to time, and if it’s not, the vehicle may lose power or not operate at all. So, while it’s good for the environment, it also requires extra care, which can be a bit of a hassle for some people who own diesel vehicles.

Here is a video explainer that dives a little deeper:

What problems can arise from the SCR system?

There are several problems that we see in SCR systems, but the one we are focusing on here is white crystal deposits that form in the SCR over time.

You might not even realize this happens until…it happens.

Over time, white crystals can form in a diesel SCR system due to the crystallization of the Diesel Exhaust Fluid (DEF), which is the liquid urea solution we all know and love that’s used in modern diesel engines equipped with SCR systems.

When the DEF is exposed to certain conditions, such as high temperatures or when it comes into contact with air, it can break down and evaporate to form these white crystal deposits. This can happen if the DEF is contaminated (or if low-quality DEF is used), if the system is not used regularly, or if the vehicle is operated in very hot conditions.

The formation of these crystals can affect the proper functioning of the SCR system, so it’s important to prevent their buildup through regular maintenance and use of appropriate cleaning products.

And that’s where we come in.

What products should I use to maintain my SCR before it leads to expensive repairs?

In Europe and other places in the world where there are more diesel vehicles, SCR maintenance is more of a well-known thing. In the US, where the number of diesel vehicles is smaller, SCR malfunctions are beginning to plague diesel owners.

We saw this coming and formulated two new products to help you avoid costly repair bills.

We have two new products for diesel owners:

Rislone DEF Crystal Clean™ Diesel DEF & SCR Emissions System Cleaner

Rislone DEF Treatment

Step one: Clean & optimize

Rislone DEF Crystal Clean™ Diesel DEF & SCR Emissions System Cleaner is a CLEANING and OPTIMIZING formula. Use this if you’ve never treated your SCR before, have white crystal (urea) buildup inside your SCR, or are having SCR-related problems (as determined by an OBD-II scan).

Rislone DEF CRYSTAL CLEAN™ is a proprietary blend of DEF (Diesel Exhaust Fluid)/AdBlue® compatible cleaning agents and surfactant detergents specifically designed to be safe to use and work on SCR (Selective Catalyst Reduction) systems.

DEF Crystal Clean™ provides a cleaning effect to the entire SCR system by working to dissolve the white crystal deposits that form in the tank, pump, heater, sender, lines, injector, decomposition tube/reactor and mixer. These deposits can interfere with the normal operation of the SCR emissions system and engine, increasing fuel consumption and reducing engine power. This reduced power can lead to operating in limp mode where the vehicle will drive slowly, or become undrivable. This process restores function and with regular use maintains efficiency of the SCR.

Step 2: Maintain

Rislone DEF Treatment is a MAINTENANCE formula. Once your SCR system is clean, this is a groundbreaking solution for keeping two of the most complex diesel systems free of white crystal deposits. Your SCR (Selective Catalyst Reduction) and DEF (Diesel Exhaust Fluid) components require maintenance, and this product makes that as easy as possible.

Just pour directly into DEF tank or into DEF bottle/cube when refilling tank. Easy as that. Never deal with SCR crystal buildup again.


Not all SCR/DEF problems are the same. If you are dealing with an issue related to your SCR/DEF system, contact us or give us a call at 800-345-6572 (8am – 5pm EST, M-F). Our US-based customer support team will be happy to walk through your situation with you. Real human experts, no confusing phone menus. We’re here if you need us.

We hope we can help you solve your SCR problem before you spend $1000+ a physical repair.