How to Fix SCR System Fault in a Peterbilt Truck

Understanding SCR System Faults in Peterbilt Trucks

SCR System Faults Peterbilt Trucks

Peterbilt trucks are known for their high performance and reliability, but like any mechanical equipment, they can experience faults that disrupt their smooth operation. One of the most common issues that Peterbilt trucks encounter is SCR system faults. Understanding what these system faults are and how to fix them can help you to keep your Peterbilt truck running smoothly and avoid unexpected breakdowns.

SCR stands for Selective Catalytic Reduction and is an emissions control technology that Peterbilt trucks use. The SCR system functions by converting the nitrogen oxide into nitrogen and water vapor. Powered by a DEF or Diesel Exhaust Fluid system, the SCR works to reduce the levels of harmful emissions released into the atmosphere by diesel engines. The SCR technology is an essential component in modern trucks, and when it malfunctions, the performance of your Peterbilt truck could be affected greatly.

The SCR system involves many intricate components, including NOx sensors, DEF pump, DEF tank, SCR catalyst, Diesel Particulate Filter (DPF), and temperature sensors. Any malfunction of these components, no matter how minor, can lead to SCR system faults in Peterbilt trucks.

The most common symptoms of SCR system faults include activated warning lights on the dashboard, reduced engine power, and difficulty in starting the truck. When you encounter these warning signs, it is essential to take action immediately. Ignoring these system faults can cause the issue to escalate, leading to costly repairs and lengthy downtime.

If you detect any SCR system faults, the first step towards fixing the problem is to diagnose the issue correctly. Peterbilt trucks store fault codes in their electronic control modules, which can help you identify system faults. However, it is important to note that fault codes vary depending on the specific model of Peterbilt truck; therefore, it is essential to consult the vehicle’s service manual for accurate information on the diagnostic codes for your truck.

Once you have diagnosed the SCR system fault correctly, the next step is to fix it. There are several steps you can take to fix the fault, depending on the specific problem you have encountered. The most common remedial procedures include replacing damaged or worn-out SCR system components, cleaning the DPF, or updating the truck’s software.

In conclusion, understanding the SCR system faults in Peterbilt trucks is vital, as it enables you to identify the problem and initiate appropriate remedial procedures. By acting quickly to correct the system faults, you can avoid costly repairs and long periods of downtime. Additionally, regular maintenance of the SCR system can prevent faults and ensure that your Peterbilt truck operates smoothly and efficiently for years to come.

Troubleshooting Common SCR System Faults in Peterbilt Trucks

SCR System Fault in Peterbilt Trucks

When it comes to maintaining a Peterbilt truck, one of the most important systems that you need to keep an eye on is the Selective Catalytic Reduction (SCR) system. This system is responsible for reducing harmful emissions and keeping your truck compliant with the latest environmental standards. However, like any other system, the SCR can encounter a range of faults at times, and it’s essential to know how to troubleshoot these issues to prevent further damage.

The Most Common SCR System Faults in Peterbilt Trucks

Most Common SCR System Faults in Peterbilt Trucks

The SCR system in your Peterbilt truck is not immune to faults and can develop various issues at different points in time. Some of the common faults that most Peterbilt truck owners encounter include

1. Poor DEF Quality

Poor DEF Quality

The DEF (Diesel Exhaust Fluid) that goes into your truck’s SCR system plays a vital role in reducing emissions. If the DEF is of poor quality, then it can cause a range of issues, including reducing the overall efficiency of the system. To rectify this, ensure that you choose a high-quality DEF from trusted suppliers and avoid buying DEF from unverified sources.

2. Failed NOx Sensors

Failed NOx Sensors

NOx sensors are an essential component of the SCR system as they help measure the amount of nitrogen oxide emissions in your exhaust. When these sensors fail, they can give out incorrect readings, causing your truck’s performance to drop considerably. If you notice a drop in your truck’s performance or a warning sign on the dashboard, then it could be due to a faulty NOx sensor. To fix the issue, replace the faulty sensor with a genuine OEM part.

When replacing the sensor, avoid purchasing cheap knock-offs as they can cause further faults in your truck’s emissions system.

3. Contamination in the SCR System

Contamination in the SCR System

The SCR system in your Peterbilt truck is susceptible to contamination from various sources such as road debris or other pollutants. Contamination can cause problems with the catalyst, which can lead to reduced performance, warning lights on the dashboard, and, in some cases, engine shutdown. Regularly inspect the system for any signs of wear and tear and clean the components regularly to prevent any build-up or contamination.

4. Corroded Injector Nozzles

Corroded Injector Nozzles

The injector nozzle in your truck’s SCR system can corrode over time, leading to reduced performance and efficiency. Corroded injector nozzles can prevent the correct amount of DEF from being delivered, causing warning lights to appear on the dashboard. If you suspect a corroded injector nozzle, have it inspected and replaced by a qualified professional.

5. Electrical Issues

Electrical Issues

An SCR system is heavily reliant on a working electrical system to function correctly. Any electrical issues, including damaged wiring or failed fuses or relays, can cause the system to stop working entirely. If you’re experiencing electrical issues with your truck’s system, it’s best to take it to a professional Peterbilt dealer to have it inspected and fixed.

In conclusion, the SCR system in your Peterbilt truck is an essential component that you need to maintain and keep in good working order. Regular maintenance and inspections can go a long way in preventing faults from occurring. However, if you do encounter any issues with your truck’s SCR system, it’s best to address them immediately to prevent any further damage and keep your truck running efficiently.

Steps to Fixing an SCR System Fault in Peterbilt Trucks

SCR system fault peterbilt

If you are experiencing an SCR (Selective Catalytic Reduction) system fault in your Peterbilt truck, it is vital for you to fix it immediately. An SCR system converts pollutants in the truck’s exhaust into less harmful substances by using a diesel exhaust fluid (DEF). The system’s failure could lead to an increase in your truck’s emissions, reduced power, and overall performance issues. Here are the steps you need to follow to fix an SCR system fault in Peterbilt trucks.

Step 1: Identify the Problem

Professional Mechanic Checking a Truck

The first thing you need to do when you detect an SCR system fault is to identify the problem. You can do this by checking the diagnostic codes stored in the truck’s onboard computer that can tell you what specifically went wrong in the system. If you are not sure about how to check the diagnostic codes, consult the manual that comes with your truck or seek the advice of a professional mechanic to help you identify the problem.

Step 2: Inspect the DEF System

DEF system in a Peterbilt truck

Once you have identified the problem in the SCR system, the next step is to inspect the DEF system. Make sure that the DEF tank is not empty, contaminated, or clogged. Check for any visible signs of damage or leaks in the system. If you notice any problems in the DEF system, it’s essential to repair or replace the damaged components accordingly.

Step 3: Test and Clean the DPF

DPF filters in a Peterbilt truck

The DPF (Diesel Particulate Filter) is a critical component of the SCR system. If you face an SCR system fault, it may result from clogged or damaged DPF filters. To fix this, you need to test and clean the DPF filters. The cleaning process involves removing the DPF filters and using specialized equipment to remove any particulate matter buildup in them. You may also need to replace the DPF filters if they are damaged beyond repair.

Cleaning or replacing the DPF filters is a crucial step in fixing an SCR system fault. It allows for improved airflow in the exhaust system, thus reducing backpressure and easing the work of other components in the SCR system.

Step 4: Reset the System

System Resetting in a Peterbilt truck

After testing, cleaning, or repairing any damaged components, the final step is to reset the SCR system. You can do this by clearing the diagnostic codes stored in the truck’s onboard computer. You should also refill the DEF tank with clean DEF fluid, which helps to carry out the selective catalytic process adequately.

Once the SCR system is reset, and the DEF tank is refilled, you will be good to go. However, it is essential to ensure that you continue monitoring your truck’s performance and checking for any future faults.


Repairing an SCR system fault in a Peterbilt truck may seem like a daunting task, but it is essential to keep the system running smoothly. By following the above steps and seeking the help of a professional mechanic if needed, you can successfully diagnose and repair any issues you encounter in the system. Remember, a properly functioning SCR system not only helps reduce harmful emissions but also improves your truck’s overall performance and fuel efficiency.

DIY SCR System Repairs for Peterbilt Trucks

Peterbilt Truck Repair

If you own a Peterbilt truck, then you know how important it is to keep your Selective Catalytic Reduction (SCR) system in good working condition. The SCR system is designed to reduce harmful emissions, which is essential for meeting environmental regulations. However, like any other vehicle component, the SCR system can experience faults that need to be addressed. Here are some DIY SCR system repairs for Peterbilt trucks that you can perform to keep your truck running smoothly.

1. Resetting the Fault Code

Peterbilt truck fault code

If your Peterbilt truck is displaying an SCR system fault code, the first step is to reset the code. To do this, you will need a diagnostic tool that is compatible with your truck’s onboard computer. Connect the tool to the OBD-II port and follow the instructions to reset the fault code. After resetting the code, monitor your truck’s performance to see if the fault code reappears. If it does, then there may be an underlying issue that needs to be addressed.

2. Cleaning the Diesel Exhaust Fluid (DEF) Injector

DEF injector cleaning

The DEF injector is responsible for delivering the diesel exhaust fluid to the SCR system, which is essential for reducing harmful emissions. Over time, the DEF injector can become clogged with debris or dirt, resulting in an SCR system fault code. To clean the DEF injector, remove it from the truck and clean it with a specialized cleaning solution. Reinstall the injector and monitor your truck’s performance to see if the fault code reappears.

3. Replacing the NOx Sensor

NOx sensor replacement

The NOx sensor is responsible for monitoring the level of nitrogen oxide in the truck’s exhaust system. If the sensor fails, the SCR system will not function properly, resulting in an SCR system fault code. To replace the NOx sensor, locate it in the exhaust system and remove it from the truck. Install the new sensor and clear any fault codes using a diagnostic tool. Monitor your truck’s performance to ensure that the fault code does not reappear.

4. Checking the DEF Quality

DEF quality check

The quality of the diesel exhaust fluid is critical to the SCR system’s performance. If the DEF is contaminated or of poor quality, then the SCR system will not function properly, resulting in an SCR system fault code. To check the DEF quality, use a DEF testing kit, which is available at most auto parts stores. If the DEF is contaminated, then drain the system and refill it with fresh DEF.


Keeping your Peterbilt truck’s SCR system in good working condition is essential for meeting environmental regulations and ensuring that your truck runs smoothly. By performing these DIY SCR system repairs, you can address common SCR system faults and keep your truck running for years to come. However, if you are unsure of how to perform these repairs, it is best to consult with a qualified technician who can assist you in troubleshooting and fixing any issues with your truck’s SCR system.

Common Mistakes to Avoid When Fixing SCR System Faults in Peterbilt Trucks

SCR system fault peterbilt

When it comes to SCR System faults in Peterbilt trucks, prevention is always better than cure. Despite this, we often see many individuals attempt to fix their system without proper knowledge and end up causing further damage, leading to higher costs and extended downtime. Here are some common mistakes you should avoid when fixing SCR System faults in Peterbilt trucks:

1. Ignoring Warning Signs

Warning signs battery

One of the most common mistakes is ignoring the warning signs. If you notice a warning light on your dashboard indicating a fault in the SCR System, do not ignore it. Any delay could lead to more damage to your vehicle. It is essential to investigate the problem immediately to identify the cause of the fault as soon as possible.

2. Cleaning the System Improperly

Cleaning tools

Another common mistake is cleaning the system improperly. Cleaning the SCR system is essential, but it must be done correctly to avoid any damage to its components. Never use anything abrasive when cleaning as it could create scratches that could lead to contamination, and always use the appropriate cleaning substance. If you are unsure about the cleaning process, it is better to seek the help of a professional mechanic.

3. Replacing Components Indiscriminately

Engine components

Replacing components indiscriminately is another mistake that can cost a lot of money and result in more damage to the vehicle. Before replacing any component in the SCR system, ensure you have correctly identified the faulty component causing the issue. It is also vital to double-check that the new component is the right one for your vehicle. The best course of action is to seek professional guidance to avoid such mistakes.

4. Not Addressing the Root Cause

Root cause analysis

When fixing an SCR System fault, it is essential to address the root cause of the issue. It is more of a short-term solution to fix symptoms and not tackle the cause of the problem. The root cause could be anything from an electrical issue to a contaminated DEF tank. Identifying and addressing the root cause is the key to avoiding future problems and unnecessary expenses, leading to reduced downtime.

5. Neglecting Regular Maintenance

Regular maintenance

One of the most significant mistakes that truck owners make is neglecting regular maintenance. Regular maintenance, including cleaning the DEF tank, checking the sensors, and replacing worn-out components, can help identify issues early, leading to quick resolutions. Neglecting regular maintenance can lead to minor issues becoming more complicated, leading to longer downtime and higher costs to repair. Your Peterbilt truck’s owner’s manual will give you details on what maintenance should be carried out and when. Don’t ignore it.

Fixing SCR System Faults in Peterbilt trucks can be complicated and requires the right knowledge, tools, and expertise. Avoiding these mistakes will help ensure that you repair the system successfully and avoid future issues. Remember, if you are unsure about anything, seek professional guidance.

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