How To Fix Scr System Fault

How to Fix SCR System Fault: A Comprehensive Guide

If you own a modern diesel vehicle or have recently encountered the dreaded SCR system fault warning on your dashboard, you may be wondering how to resolve this issue effectively. While it can be frustrating to see such a warning, the good news is that fixing a SCR system fault is typically not as complicated as it may seem. In this guide, we will walk you through the necessary steps to troubleshoot and potentially fix your vehicle’s SCR system fault.

Understanding the SCR System

Before we delve into the troubleshooting process, let’s briefly discuss what the SCR (Selective Catalytic Reduction) system is and how it functions in your vehicle. The SCR system is an emissions control technology installed in diesel vehicles to reduce harmful nitrogen oxide (NOx) emissions, which contribute to air pollution.

The SCR system works by injecting a precise amount of diesel exhaust fluid (DEF), also known as AdBlue, into the exhaust stream. This fluid reacts with the harmful NOx emissions in the catalytic converter, converting them into harmless nitrogen gas and water vapor.

Troubleshooting a SCR System Fault

When your vehicle’s SCR system experiences a fault, it can result in reduced engine performance and increased emissions. Here are some steps you can take to troubleshoot and potentially fix the SCR system fault:

1. Check the DEF Level

The first and simplest step is to check the level of diesel exhaust fluid in your vehicle’s DEF tank. Low DEF levels can trigger a system fault warning. Locate the DEF tank, usually found near the fuel tank, and ensure it has an adequate amount of fluid. If the level is low, refill it with the recommended DEF, following the manufacturer’s instructions.

2. Inspect for DEF System Leaks

If the DEF tank level is sufficient, the next step is to inspect the entire DEF system for any leaks or damage. Look for visible signs of fluid leakage around the tank, lines, connections, and the DEF injector. If you spot any leaks, it is crucial to repair them promptly to prevent further SCR system malfunctions.

3. Check for Faulty Sensors

Faulty sensors can also cause SCR system faults. The most common sensor associated with the SCR system is the NOx sensor. Using an OBD-II scanner, retrieve any error codes related to the SCR system. If the error code indicates a faulty sensor, consult your vehicle’s manual or contact a professional mechanic to determine the appropriate course of action, such as sensor replacement or calibration.

4. Clean or Replace the SCR Catalyst

The SCR catalyst is responsible for the chemical reactions that occur within the SCR system. Over time, it can become contaminated or damaged, resulting in system faults. If all other components seem to be functioning correctly, consider cleaning or replacing the SCR catalyst. Consult a qualified technician or your vehicle’s manual for guidance on the specific procedure for your vehicle model.

5. Resetting the System

Once you have resolved the underlying issue causing the SCR system fault, it is essential to reset the fault codes stored in your vehicle’s onboard computer. This step will clear the warning message from your dashboard and ensure that the system recognizes the remedial actions you have taken. Remember to use an OBD-II scanner or take your vehicle to a professional mechanic to perform the system reset.

Preventing Future SCR System Faults

Now that you have successfully resolved the SCR system fault, taking preventive measures can help avoid future issues. Follow these recommendations to maintain a healthy SCR system:

  • Regularly check the DEF fluid level and refill it as needed, adhering to the manufacturer’s guidelines.
  • Only use high-quality DEF fluid to ensure optimal system performance and longevity.
  • Inspect the DEF system components periodically for leaks or damage, fixing any issues promptly.
  • Adhere to the recommended vehicle maintenance schedule outlined in your owner’s manual, including regular SCR system inspections.

By following these preventive steps and addressing any system faults promptly, you can ensure the longevity and proper functioning of your vehicle’s SCR system, contributing to a cleaner and healthier environment.


Encountering a SCR system fault on your diesel vehicle can be disconcerting, but understanding the process of troubleshooting and resolving the issue empowers you to take the necessary actions. By following the steps outlined in this comprehensive guide, you can effectively troubleshoot and potentially fix common SCR system faults. Remember, if you feel uncertain or overwhelmed, it is always advisable to consult a professional mechanic with expertise in SCR systems to ensure your vehicle receives the best possible care.

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