How To Fix SCR System Fault – Expert Tips You Should Know

Learning how to fix SCR system fault is an important thing to understand. After all, it is an important component that helps with minimizing nitrogen oxide emission from your vehicle.

If your vehicle uses diesel for fuel, then you need to keep your SCR system in check to avoid some issues. 

Keep in mind that diesel uses chemical particles, which can wreak havoc to the environment. For instance, ammonia is a primary SCR system source required for cleaning nitrogen oxide from the toxic chemicals in the air emitted from your truck’s engine. 

Your SCR system is installed at the back of the truck engine right between the furnace economizer and the air heater. Then ammonia is injected through your ammonia injection grid. Once the SCR system fails, this is not just harmful to the truck but also to the environment. 

Find out what you need to know about fixing the SCR system fault and other key tips to keep in mind. Let’s get right into it. 

how to fix scr system fault

How To Fix SCR System Fault

First of all, let us talk about the SCR system on your truck. Basically, this is an intelligent component that separates harmful components from your truck and exhausting air each time diesel is burned. The by-products such as carbon dioxide, nitrogen, and similar components are emitted through your exhaust pipe. Hence, the SCR system is responsible for breaking these chemical bonds into a more eco-friendly substance. 

For example, Nitrogen oxide becomes broken down into water and nitrogen through DFL and ammonia. What car manufacturers wish to achieve is to minimize the emission level of nitrogen oxide from trucks. 

Your vehicle’s SCR system works in a simple and straightforward process. The front portion is connected to your main engine. Then your engine burns the fuel and generates nitrogen oxide. This will then enter the aqueous area of your SCR system. 

Afterwards, the Diesel Exhaust Fluid is combined with your engine’s exhaust air and then begins a chemical reaction. Throughout this process, the nitrogen oxide gets broken down into several components such as water, carbon dioxide, oxygen, and nitrogen. 

Once the particle is broken down, it is then filtered further for purification purposes, Then, these particles pass through your tail pipeline. What this does is to let your engine emit gas that is not harmful to the environment. Hence, it is free from nitrogen oxide gas as the SCR system utilizes ammonia in cleaning and separating the harmful gas into a more valuable type of gas.

This is the reason why the system is called “selective”.

If your vehicle is experiencing a SCR system fault, it means that the unit does not work as it should. Repair may be required since damage is likely to arise when the issue persists. Your SCR system is also unable to filter and produce less harmful gasses into the environment, which can be a huge concern. 

Usually, your truck may become unable to start when such a problem occurs. To make matters worse, nitrogen oxide gets mixed into the atmosphere and wreaks havoc to the environment. 

As we know, it’s connected to the main engine and the tail pipeline; if this system fails to work, that means danger for both the truck and our environment.

The truck will not start if a small problem shows in the SCR system, and much nitrogen oxide will get mixed into our atmosphere. 

There are a few reasons why your SCR system may fail. For instance, ammonia may get stuck and clog up the injection grid. It is also possible that there is an issue with your DEF fluid, which causes the SCR system to malfunction. A few other issues may arise, which is why it is important to stay on top of the condition of your vehicle to avoid these issues from occurring. 

Prior to starting your vehicle, make it a habit to inspect your SCr system and sensors. In case you observe some symptoms of damage, it is best to have the problem addressed before things get worse. 

Some of the most common signs of damage include a higher temperature or overheating, which may be followed by a diode or circuit burning. If you allow the problem to persist, this can cause the system to fail permanently. 

You may also begin to notice that your SCR warning light starts to illuminate. This light is an effective indicator that the maximum driving distance damage has been achieved. For instance, if your maximum driving distance is at 250 miles or 402 kilometers, the light will switch on. You may also hear an audible sound while at the same time turning the SCR system ignition switch on. 

When there is failure on your SCR system, the warning light tends to flash. On the other hand, if the light does not get activated, it means there is no issue at all with your SCR system.

Testing Your SCR System

What’s good about the SCR system is that it is relatively inexpensive to install. This is why heavy duty diesel trucks often come with this system. 

If you suspect an issue with your SCR, the best thing to do is test it with an ohmmeter. Begin by connecting your positive lead to an anode part. Then connect your cathode side onto your negative lead. 

Follow the designated resistance value presented in your ohmmeter.  When there is a high resistance value, this means that your SCR system is working just right. On the other hand, a low resistance value presents a fault to the system. Hence, you will need to replace or repair your old SCR system. 

If you wish to improve the lifespan of your truck engine, it may help to do a SCR system delete. Deleting your SCR system completely may also help in cleaning the engine and improving the system’s workability.


Considering the importance of the SCR system, it is essential to make sure that it is working properly. This is why it is imperative to inspect it regularly and check for faults to get the unit replaced or repaired promptly before it is too late.

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