SCR System Fault [Meaning, Causes & Solution] – (2024)

The Selective Catalytic Reduction (SCR) technology plays an important role in lowering emissions in diesel vehicles, contributing to a cleaner and more sustainable environment.

However, the SCR system, like any complex system, can develop faults that require quick attention.

In this article, I will discuss the meaning of an SCR system fault on your Truck, the common causes of its failure, how to troubleshoot it, and more. Let’s get to it.

What is a SCR System Fault?

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A System Fault refers to a malfunction or failure in the Selective Catalyst Reduction system of a vehicle.

The SCR system is responsible for reducing emissions by injecting diesel exhaust fluid (DEF) into the exhaust stream to react with nitrogen oxides (NOx).

When a System Fault occurs, it indicates a problem that requires attention. The warning is displayed on the dashboard, alerting the driver to the issue.

Causes can vary, including sensor malfunctions, DEF supply problems, or catalyst issues.

Operating a vehicle with a faulty SCR system can lead to increased emissions, reduced fuel efficiency, and potential engine or emissions component damage. The vehicle may enter a reduced power mode, limiting performance and speed.

What Causes SCR System Fault?

A system fault in a Diesel Selective Catalytic Reduction (SCR) system can be caused by several factors, including:

Insufficient DEF Fluid:

DEF (Diesel Exhaust Fluid) is a critical component in the SCR system. If the DEF fluid level is too low or depleted, the SCR system may trigger a fault.

This can happen if the DEF tank is not refilled regularly or if there is a leak in the system.

Contaminated DEF Fluid:

If the DEF fluid becomes contaminated with impurities or other substances, it can cause problems in the SCR system.

Contamination can occur due to using improper or low-quality DEF fluid or if there is a contamination source in the DEF storage or delivery system.

Dirty or Clogged Filters:

The SCR system contains various filters, such as the DEF filter and the diesel particulate filter (DPF).

If these filters become dirty or clogged, it can affect the performance of the SCR system and trigger a fault. Regular maintenance and cleaning of the filters are important to prevent this issue.

Mechanical Issues:

Mechanical problems within the SCR system components, such as faulty sensors, malfunctioning injectors, or damaged catalyst elements, can also lead to system faults.

These issues can disrupt the proper operation of the SCR system and trigger error codes or warnings.


Excessive heat can impact the SCR system’s components and cause faults.

High temperatures can damage the SCR catalyst or the temperature sensors, leading to malfunctions.

Overheating can result from operating the vehicle under extreme conditions, such as heavy loads, excessive idling, or towing.

It’s worth noting that this is a general overview, and specific diagnostic procedures and troubleshooting steps may vary depending on the exact model and year of the vehicle.

The Solution to an SCR System Fault on a Diesel Vehicle

When faced with a system fault in the SCR (Selective Catalytic Reduction) system, there are several steps you can take to address the issue.

First, check the DEF (Diesel Exhaust Fluid) tank to ensure it has an adequate amount of fluid.

If the level is low, refill it with the recommended DEF fluid. Make sure to use DEF fluid that meets the vehicle manufacturer’s specifications to avoid potential problems.

Next, verify the quality of the DEF fluid. Ensure it is not contaminated, as contamination can cause SCR system faults.

If you suspect contamination, drain the DEF tank and replace the fluid with fresh, uncontaminated DEF fluid.

Inspect the filters in the SCR system, including the DEF filter and the diesel particulate filter (DPF).

If the filters are dirty or clogged, clean or replace them as necessary. Consult the vehicle’s manual or seek professional assistance for specific instructions on accessing and maintaining the filters.

If the above steps don’t resolve the system fault, check for mechanical issues within the SCR system.

This involves examining sensors, injectors, catalyst elements, and other components. Faulty components may need to be repaired or replaced by a qualified technician.

After addressing the underlying issue, clear any fault codes stored in the vehicle’s computer system. This can typically be done using a diagnostic tool or by visiting a dealership or authorized service center.

If you’re unable to resolve the system fault or are uncomfortable performing the troubleshooting steps yourself, seek assistance from a dealership or an authorized service center.

Their trained technicians have the expertise to diagnose and repair SCR system faults accurately.

It’s important to consult your vehicle’s manual or contact a professional for specific instructions and guidance tailored to your vehicle model and year.

Additional Resources

SCR System Fault [Meaning, Causes & Solution] – (2024)
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