How to Fix SCR system fault Kenworth? – Instructions and Videos

When we talk about diesel fuel, one of the most common unknown words is SCR.

What does SCR mean on a Kenworth?

SCR represents an active emissions control technology system in many advanced diesel engines. SCR or  Selective Catalytic Reduction is after-treatment technology that utilizes a reductant (DEF) to convert NOx to harmless nitrogen and water.

SCR error Kenworth

A technique known as selective catalytic reduction, or SCR for short, is good for the environment because it may help decrease the amount of nitrogen oxide emissions produced by your vehicle or other machinery. This is a trait that is typical of motor vehicles that are fuelled by diesel.

Diesel fuel has an exceptionally high concentration of various chemical particles, some of which might be toxic. Ammonia is a necessary component of the selective catalytic reduction (SCR) system that removes nitrogen oxides (NOx) from diesel vehicles’ exhaust emissions.

The ammonia is delivered via the ammonia injection grid, which is located behind the truck engine, between the air heater and the furnace economizer. If this process fails, not only will our jealousy be affected, but so will that vehicle.

Science and technology have led to the development of the SCR system. Toxic fumes from a truck or other vehicle’s exhaust may be filtered out using this device. Nitrogen, carbon dioxide, and other airborne pollutants are released via the exhaust pipe as a byproduct. It’s impossible to track how much hazardous air is emitted by diesel-powered vehicles.

Chemical bonds containing harmful chemicals are the primary objective of SCR systems. A mixture of Ammonia and DFL is used to break down nitro oxide into nitrogen and water. Trucks’ nitric oxide emission levels are a concern for automakers.

What Is the Process of an SCR System?

Simple is the operating method of the Selective Catalytic Reduction system (SCR). To connect to the main engine, the front half of this unit is used. The engine creates Nitrogen Oxide when it consumes gasoline; this gas travels through the SCR system’s aqueous region and into the atmosphere.

SCR proccess

A chemical reaction occurs when Diesel Exhaust Fluid (DEF) is combined with exhaust air from an engine. Nitrogen Oxide undergoes this transformation, yielding Nitrogen, Oxygen, Carbon Dioxide, and Water as byproducts.

They travel through a series of additional filters to cleanse the separated particles. The truck engine can now run without emitting any NOx gas thanks to this solution, making it more environmentally friendly. It is named a Selective system because it employs ammonia as the primary source of cleaning and separating harmful gas into helpful gas.

What Is the Significance of a Truck SCR System Fault?

It is necessary to fix the Selective Catalytic Reduction (SCR) system if it has an SCR system defect since this would result in significant damage. A contemporary truck’s SCR system is critical for removing harmful particulates from the exhaust air. In other words, if this system goes haywire, it might put the vehicle and our environment in peril.

Minor problems in the SCR system mean the vehicle won’t start, releasing large amounts of nitrogen oxide into the environment.

Is there anything that can go wrong with the SCR system?

If the ammonia becomes trapped in the injection grid or there is a problem with the DEF fluid, the SCR system may fail for several reasons. You can’t count the number of problems in the system, but you must be alert and careful.

You should check the SCR system and all sensors before the truck is started; rectify it if there is a problem before driving off. The circuit or diode may burn if the temperature increases to a high degree, resulting in the system’s irreversible failure.

SCR Warning Light – What Does It Mean?

The SCR (selective catalytic reduction) warning light is activated for maximum driving distance. When the maximum driving distance is reached, the indicator light comes on. As soon as the ignition switch for your SCR system is turned on, a sound is produced.

When anything goes wrong, this light will flash; otherwise, it will stay off if everything is well.

What’s the big deal about SCR?

Nitrogen, Oxygen, Carbon Dioxide, and Water are all separated from Nitro Oxide in the SCR system. As a bonus for the environment, this procedure also helps to purify the harmful exhaust from diesel engines.

This approach is more economical since it needs fewer expenditures. There is an SCR system in all large diesel vehicles.

How to Fix SCR system fault Kenworth?

You’ll need an Ohmmeter to check an SCR system for functionality. After that, follow these steps:

  • As a first step, you’ll need to connect the anode and cathode leads.
  • The second step is to observe the ohmmeter’s resistance reading.
  • If your SCR system has a high resistance value, you’re good to go; if your SCR system has a low resistance value, you’re not. A new or repaired SCR system is required.


You may avoid emitting harmful Nitrogen Oxide into the atmosphere by installing an SCR system in your vehicle. You may detect circuit failure, engine deceleration, DEF issues, and other problems with this method. For example, if your Vehicle screen says 60 minutes to derate, it implies you may operate that truck for 60 minutes. To complete the process, you must shut off your engine. The truck’s speed will drop if it does not.

Because of this, repairing or resolving the root cause of an SCR system malfunction begins with identifying the issue.

What exactly does SCR delete mean?

A system deletion is required if you want to extend the life of your diesel truck engine. SCR systems need to be removed entirely if you want to clean your machine and improve the SCR system.


What are some of the unique issues with SCR?

Creating an environment that is safe for both automobiles and the atmosphere is one of the main benefits of Selective Catalytic Reduction (SCR). Pollutants are converted to harmless particles when DEF is sprayed into the exhaust air of the engine. If your car has an SCR system, you’ll need to know how to diagnose and fix SCR problems.

On a Mack truck, what does SCR mean?

Construction sites use Mack trucks, which can carry large machinery. They are quick and economical. Mack trucks are increasingly equipped with SCR systems, which not only save money but also assist in lowering atmospheric levels of the carcinogen Nitro Oxide.

What does the SCR system on a Volvo truck consist of?

One of the best truck manufacturers, Volvo, has an SCR system in its vehicles. This saves customers money on gasoline and helps protect the car from spewing harmful emissions into the air we breathe.

What does Kenworth’s SCR system do?

A Kenworth truck is equipped with an SCR system, which means that the exhaust air produced by these vehicles is environmentally benign. Nitrogen and Oxygen are not toxic to humans; thus, a truck’s SCR system may break down NOx into these two substances. An excellent worldwide cause like this can only be good for Kenworth.

When someone received a notice that power was limited due to an SCR system malfunction and two check engine lights were illuminated, along with a full DEF tank and a flashing red light, what may be the cause?

Regarding this problem. Consequently, there is a problem with the SCR system. This often refers to NOX levels that cannot be fulfilled. In this sort of worry, you must retrieve the faults, and a NOX monitoring test must be performed to determine which component of the SCR system the ECM is indicating has a problem. Once the device has been fixed and NOX levels have returned to permissible levels, the ECM will switch off all the lights.

Does your brain believe I’m low on DEF since my red DEF indicator is flickering even if my tank indicates a whole level?

The QLS sensor may have malfunctioned. A lot of them have gone bad recently. In the SCR system, a red light indicates a problem with DEF quality.

Is it simple to make the switch, or does it take a long time?

2-350 is the range of the sensors. Replacing them isn’t difficult, depending on how your DEF tank is set up. Once the repair is complete, the unit must be linked to a scan tool to conduct a parked regen and monitor NOX levels.


The SCR system is evidence of your technical advancement in this time of fast industrial and technological progress. This system filters engine air by injecting DEF and is also known as an active emission control system. The most hazardous substance that may devastate our ecosystem is nitro oxide. By using the SCR system, trucks can reduce them to harmless particles. We’ve done our best to cover all you need to know about what an SCR system problem in a car signifies. Let me know if there is anything more I can help you with.

Robert Aksamit

Robert Aksamit

Robert Aksamit is a mechanical engineer and automotive industry expert. Robert was born in Minnesota and worked in the US automotive industry for 25 years. He is highly regarded for his passion and dedication to continually improving vehicles in response to customer feedback. Robert has a keen eye for sourcing the best vehicle components and materials on the market and is always looking for ways to enhance the user experience. As a writer, Robert covers automotive-related topics. Read more on Robert Aksamit's about page. Contact Robert:

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