BS6 Truck Error Codes Related to SCR (Selective Catalytic Reduction) Systems: A Technical Guide

 BS6 Truck Error Codes Related to SCR (Selective Catalytic Reduction) Systems: A Technical Guide

The Selective Catalytic Reduction (SCR) system is an essential part of BS6-compliant trucks, designed to reduce nitrogen oxide (NOx) emissions. As environmental regulations become more stringent, the SCR system plays a crucial role in ensuring that trucks meet the required emission standards. However, with the introduction of advanced technology comes the potential for technical issues and error codes. SCR error codes are some of the most common faults that BS6 truck drivers and fleet operators encounter.

In this detailed guide, we will provide a technical dive into how the SCR system works, the common error codes associated with it, and how to troubleshoot and fix these errors to keep your trucks compliant with BS6 standards.

Table of Contents

1. Introduction to the SCR System in BS6 Trucks

2. How the SCR System Works

3. Common Causes of SCR System Errors in BS6 Trucks

4. Common SCR Error Codes in BS6 Trucks

1. P20EE – SCR NOx Catalyst Efficiency Below Threshold

2. P203F – Reductant Level Too Low

3. P204F – Reductant System Performance Issue

4. P207F – SCR NOx Catalyst Temperature Too Low

5. P2201 – NOx Sensor Circuit High Voltage

5. How to Fix SCR System Error Codes in BS6 Trucks

6. Preventive Measures to Avoid SCR Error Codes

7. Conclusion

1. Introduction to the SCR System in BS6 Trucks

The Selective Catalytic Reduction (SCR) system is a vital emission control technology in BS6 trucks. Its primary function is to reduce harmful nitrogen oxides (NOx) from diesel exhaust gases, which are a significant contributor to air pollution. By injecting a solution called AdBlue (Diesel Exhaust Fluid, DEF) into the exhaust stream, the SCR system converts NOx into harmless nitrogen and water vapor.

While the SCR system is highly effective at reducing emissions, it is also complex and relies on several components to work correctly. These include the NOx sensors, temperature sensors, AdBlue dosing system, and the SCR catalyst. When any part of this system malfunctions, the truck’s On-Board Diagnostics (OBD-II) system generates error codes to signal the issue.

2. How the SCR System Works

The SCR system operates by injecting a urea-based solution, known as AdBlue, into the exhaust gases as they leave the engine. Here’s a step-by-step look at how the SCR system works:

1. Exhaust Gas Enters the SCR Catalyst: As the exhaust gases pass through the DPF and leave the engine, they enter the SCR catalyst.

2. AdBlue Injection: The SCR system injects a precise amount of AdBlue into the exhaust stream. The heat from the exhaust gases breaks down the AdBlue into ammonia (NH3).

3. Chemical Reaction: Inside the SCR catalyst, the ammonia reacts with the NOx in the exhaust gases. This reaction converts the NOx into nitrogen (N2) and water vapor (H2O), both of which are harmless.

4. Final Exhaust Emission: After this process, the cleaned exhaust gases are released into the atmosphere, with significantly lower NOx levels.

The SCR system is constantly monitored by sensors to ensure it operates efficiently. However, if any part of the system fails, it can lead to a range of error codes that must be addressed to maintain compliance with BS6 emission standards.

3. Common Causes of SCR System Errors in BS6 Trucks

Several factors can lead to SCR system errors in BS6 trucks. Here are the most common causes:

Low or Contaminated AdBlue: The SCR system relies on a consistent supply of high-quality AdBlue. If the AdBlue tank runs low or the fluid is contaminated, it can cause the system to malfunction and trigger error codes.

Faulty NOx Sensors: The NOx sensors monitor the amount of nitrogen oxide in the exhaust gases before and after the SCR catalyst. If these sensors fail, they can cause the system to incorrectly assess its efficiency, leading to error codes.

Clogged or Damaged SCR Catalyst: Over time, the SCR catalyst can become clogged with soot or damaged, reducing its effectiveness in reducing NOx emissions.

AdBlue Injection Issues: If the AdBlue dosing valve or injectors are malfunctioning, the system may not inject the correct amount of AdBlue, leading to error codes.

4. Common SCR Error Codes in BS6 Trucks

Let’s take a closer look at the most common error codes associated with the SCR system in BS6 trucks, their meanings, and how to address them.

1. P20EE – SCR NOx Catalyst Efficiency Below Threshold

What it means:

The P20EE code indicates that the SCR system is not reducing NOx emissions to the required level. This can occur if the SCR catalyst is clogged, damaged, or if there is a problem with the NOx sensors.

Common Causes:

Faulty NOx sensors

Clogged or damaged SCR catalyst

Low-quality or contaminated AdBlue

How to Fix:

Test and replace the NOx sensors if they are faulty.

Inspect the SCR catalyst for blockages or damage and clean or replace it as necessary.

Ensure that the AdBlue tank is full and that the fluid is of the correct quality.

2. P203F – Reductant Level Too Low

What it means:

The P203F code indicates that the AdBlue level in the tank is too low for the SCR system to function properly.

Common Causes:

Low AdBlue levels

Faulty AdBlue level sensor

How to Fix:

Refill the AdBlue tank with the correct fluid.

Inspect the AdBlue level sensor and replace it if it is faulty.

3. P204F – Reductant System Performance Issue

What it means:

The P204F code signals that there is a performance issue with the AdBlue injection system, which could be due to a problem with the injectors, dosing module, or the AdBlue pump.

Common Causes:

Malfunctioning AdBlue injector or pump

Blockages in the AdBlue lines

How to Fix:

Check the AdBlue injector and dosing module for malfunctions. Replace any faulty components.

Ensure that the AdBlue lines are free from blockages.

4. P207F – SCR NOx Catalyst Temperature Too Low

What it means:

This code indicates that the temperature inside the SCR catalyst is too low for efficient NOx reduction. This is typically caused by the engine not reaching sufficient operating temperature or a fault in the exhaust temperature sensor.

Common Causes:

Short trips or low-speed driving

Faulty temperature sensor

How to Fix:

Ensure that the truck is operated at highway speeds periodically to raise the exhaust temperature.

Inspect and replace the exhaust temperature sensor if necessary.

5. P2201 – NOx Sensor Circuit High Voltage

What it means:

The P2201 code indicates that there is an issue with the NOx sensor circuit, such as high voltage or a short. This can prevent the SCR system from accurately measuring NOx levels.

Common Causes:

Faulty NOx sensor

Damaged wiring or connectors

How to Fix:

Test the NOx sensor and replace it if it is malfunctioning.

Inspect the wiring and connectors for damage and repair or replace them as needed.

5. How to Fix SCR System Error Codes in BS6 Trucks

When an SCR system error code is triggered, follow these steps to resolve the issue:

1. Scan the Truck for Error Codes: Use an OBD-II diagnostic tool to identify the specific error codes related to the SCR system.

2. Inspect the SCR Components: Check the AdBlue system, NOx sensors, and SCR catalyst for any signs of malfunction or damage.

3. Replace Faulty Components: If the sensors, injectors, or SCR catalyst are found to be faulty, replace them with new, OEM-approved parts.

4. Refill the AdBlue Tank: Ensure the AdBlue tank is full and that the fluid meets the required specifications.

5. Reset the Error Codes: After addressing the issue, use the diagnostic tool to clear the error codes from the truck’s system.

6. Preventive Measures to Avoid SCR Error Codes

To avoid SCR system error codes, follow these preventive maintenance tips:

Regularly Refill the AdBlue Tank: Always ensure the AdBlue tank is topped off with high-quality fluid.

Use the Truck on Highways: Regular highway driving ensures that the exhaust reaches the necessary temperature for the SCR system to function efficiently.

Inspect the SCR Catalyst Periodically: Check the SCR catalyst for any signs of clogging or damage, especially if error codes frequently appear.

Replace NOx Sensors When Necessary: Faulty NOx sensors are a common cause of SCR system issues, so replace them as soon as they start to show signs of malfunction.

7. Conclusion

The SCR system is a critical part of keeping BS6 trucks compliant with emission standards, but it is also prone to error codes if any of its components malfunction. By understanding the common causes of SCR error codes and knowing how to fix them, truck drivers and fleet operators can minimize downtime, improve truck performance, and ensure compliance with BS6 regulations. Regular maintenance and timely troubleshooting are key to keeping your SCR system running smoothly.