SPN 4364: NOx Efficiency Below Threshold - SCR System Fault

Understanding SPN 4364: NOx Efficiency Below Threshold - SCR System Fault

The Selective Catalytic Reduction (SCR) system plays a crucial role in reducing nitrogen oxide (NOx) emissions from diesel engines. When the SPN 4364 fault code appears, it indicates that the SCR system is not performing efficiently, leading to higher-than-acceptable NOx levels. This issue needs immediate attention to maintain emission compliance and engine efficiency.

## Causes of SPN 4364

Several factors can trigger this fault code, including:

1. DEF Quality Issues – Poor or contaminated Diesel Exhaust Fluid (DEF) can cause inefficiencies in the SCR system.

2. NOx Sensor Malfunction – A faulty upstream or downstream NOx sensor may provide incorrect readings, triggering the fault.

3. DEF Dosing Malfunction – A clogged DEF injector or malfunctioning dosing unit can lead to improper DEF delivery.

4. SCR Catalyst Degradation – Over time, the SCR catalyst can become less effective due to aging or contamination.

5. Exhaust System Leaks – Any leaks before or after the SCR catalyst can impact NOx conversion efficiency.

6. ECU Software or Calibration Issues – An outdated Engine Control Unit (ECU) software may cause incorrect diagnostics.

## Symptoms of SPN 4364

If your vehicle has this fault code, you may notice:

- Check engine light illuminated

- Reduced engine power or derate mode

- Increased DEF consumption

- Higher exhaust emissions

## Troubleshooting and Fixes

To resolve the SPN 4364 fault code, follow these steps:

### 1. Check and Replace DEF if Necessary

- Use high-quality DEF that meets ISO 22241 standards.

- Drain and refill the DEF tank if contamination is suspected.

### 2. Inspect and Replace NOx Sensors

- Perform a diagnostic scan to check sensor performance.

- Replace faulty sensors and clear fault codes.

### 3. Test DEF Dosing System

- Inspect the DEF injector for clogging and clean if necessary.

- Ensure the dosing pump is functioning correctly.

### 4. Evaluate SCR Catalyst Condition

- Conduct an SCR efficiency test to determine catalyst health.

- Replace the catalyst if it has degraded beyond repair.

### 5. Inspect the Exhaust System

- Check for leaks or damaged components.

- Repair or replace any compromised parts.

### 6. Update ECU Software

- Check for available software updates from the manufacturer.

- Reflash the ECU if needed.

## Final Thoughts

Ignoring the SPN 4364 fault code can lead to costly repairs, compliance violations, and decreased engine performance. Regular maintenance, high-quality DEF, and prompt troubleshooting can help prevent this issue. If the problem persists, seek professional diagnostic services to ensure proper functioning of the SCR system.