Urgency and Driving Considerations
SPN 520373 indicates a malfunction in the Aftertreatment Outlet NOx Sensor, a critical component of the Selective Catalytic Reduction (SCR) system. While immediate vehicle shutdown is not necessary, prompt attention is crucial.
Driving Recommendations:
- Short-term driving is possible, but prolonged operation may increase emissions and potentially damage the engine.
- Schedule a service appointment as soon as possible.
- Be aware of potential reduced engine performance and decreased fuel efficiency.
In our workshop, we’ve encountered SPN 520373 fault codes across various European car makes, with Volvo, Mercedes-Benz, and MAN trucks being the most frequent offenders. We’ve noticed this issue is particularly common in diesel engines equipped with SCR systems. From our experience, the fault is often triggered by a faulty NOx sensor, but we’ve also seen cases where wiring issues or exhaust leaks were the culprits. Interestingly, we’ve found that Mercedes vehicles tend to be more sensitive to this fault, often requiring sensor replacement even when readings are only slightly out of spec. In contrast, Volvo trucks seem more resilient, sometimes clearing the code after a few drive cycles without intervention. Overall, while SPN 520373 isn’t exclusive to European vehicles, we’ve definitely seen it more often in these makes compared to their American or Asian counterparts.
Detailed Code Information
SPN 520373 is a generic code related to the SCR system’s NOx sensor functionality, common across various vehicle manufacturers using SCR technology.
Key Components Involved:
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- Aftertreatment Outlet NOx Sensor
- Diesel Exhaust Fluid (DEF) System
- SCR Catalyst
Role of Components:
- The NOx sensor measures nitrogen oxide levels in the exhaust after treatment.
- The DEF system injects urea solution to reduce NOx emissions.
- The SCR catalyst facilitates the conversion of NOx into harmless nitrogen and water.
Common Causes
- Faulty NOx sensor
- Wiring issues or connector problems
- DEF quality or contamination
- SCR catalyst degradation
- Engine Control Module (ECM) software issues
Diagnostic Procedure
- Connect an OBD-II scanner and verify the SPN 520373 code.
- Check for additional related fault codes.
- Inspect the NOx sensor wiring and connections for damage or corrosion.
- Verify DEF quality and level.
- Use a multimeter to test the NOx sensor circuit for proper voltage and resistance.
- Perform a visual inspection of the SCR catalyst for signs of damage.
- Use advanced diagnostic tools to analyze NOx sensor data and SCR system performance.
Solutions
- Replace faulty NOx sensor
- Repair or replace damaged wiring
- Flush and refill DEF system with high-quality fluid
- Replace SCR catalyst if degraded
- Update ECM software if necessary
Prevention
- Regular maintenance of the SCR system
- Use high-quality DEF fluid meeting ISO 22241 specifications
- Address check engine lights promptly
- Perform periodic system scans
Repair Costs
Parts:
- NOx Sensor: $200 – $600 (€170 – €510)
- SCR Catalyst: $1,000 – $3,000 (€850 – €2,550)
- DEF Fluid: $20 – $50 (€17 – €43) per 2.5 gallons (9.5 liters)
Labor:
- Diagnostic Time: 1-2 hours
- Sensor Replacement: 1-3 hours
- Catalyst Replacement: 3-6 hours
Total Cost Estimate:
$300 – $4,000 (€255 – €3,400) depending on the required repairs
Repair Guide
- Disconnect the battery
- Locate the faulty NOx sensor (typically near the SCR catalyst)
- Unplug the electrical connector
- Remove the sensor using a specialized socket or wrench
- Install the new sensor, ensuring proper torque (typically 40-50 Nm or 29.5-36.9 ft-lbs)
- Reconnect the electrical connector
- Clear fault codes and perform a system reset
- Test drive to confirm proper operation
Related Issues and Fault Codes
- SPN 3226 (Aftertreatment 1 Outlet NOx Sensor Circuit)
- SPN 3216 (Aftertreatment 1 Intake NOx Sensor Circuit)
- SPN 1080 (DEF Tank Level)
- SPN 3361 (SCR Catalyst Efficiency)
These related codes often indicate broader issues within the SCR system and may require comprehensive diagnostics and repairs.
By addressing SPN 520373 promptly and thoroughly, engineers and mechanics can ensure optimal SCR system performance, maintain emissions compliance, and prevent potential engine damage.
SPN 520373 Comprehensive FAQ
What does SPN 520373 indicate?
SPN 520373 indicates a malfunction in the Aftertreatment Outlet NOx Sensor, which is a critical component of the Selective Catalytic Reduction (SCR) system.
Is it safe to continue driving with SPN 520373 active?
Short-term driving is possible, but it’s not recommended for prolonged periods. Schedule a service appointment as soon as possible to prevent increased emissions and potential engine damage.
What are the key components involved with SPN 520373?
The key components are the Aftertreatment Outlet NOx Sensor, Diesel Exhaust Fluid (DEF) System, and SCR Catalyst.
What are common causes of SPN 520373?
Common causes include a faulty NOx sensor, wiring issues, DEF contamination, SCR catalyst degradation, and ECM software issues.
How do I diagnose SPN 520373?
Start by connecting an OBD-II scanner, then inspect wiring, check DEF quality, test the NOx sensor circuit, and inspect the SCR catalyst.
What are the potential solutions for SPN 520373?
Solutions may include replacing the NOx sensor, repairing wiring, flushing the DEF system, replacing the SCR catalyst, or updating ECM software.
How can I prevent SPN 520373 from occurring?
Regular maintenance of the SCR system, using high-quality DEF fluid, addressing check engine lights promptly, and performing periodic system scans can help prevent this issue.
What is the estimated cost to repair SPN 520373?
Repair costs can range from $300 to $4,000 (€255 – €3,400) depending on the required repairs.
How long does it take to replace a NOx sensor?
NOx sensor replacement typically takes 1-3 hours.
Are there any related fault codes to SPN 520373?
Yes, related codes include SPN 3226, SPN 3216, SPN 1080, and SPN 3361.
Can a faulty NOx sensor cause other issues in the vehicle?
Yes, it can lead to increased emissions, reduced engine performance, and decreased fuel efficiency.
How often should the NOx sensor be replaced?
NOx sensors typically last about 6,000 hours or 300,000 km (200,000 mi), but this can vary based on operating conditions.
Can I clean the NOx sensor instead of replacing it?
Cleaning is not recommended as it may damage the sensor. If attempted, it will likely void any warranty.
What’s the difference between inlet and outlet NOx sensors?
They operate at different NOx concentration levels and may communicate differently. They are not interchangeable.
Do NOx sensors require programming after installation?
Generally, no programming is required, but follow the manufacturer’s instructions for your specific vehicle.
How long does it take for the ECU to recognize a new NOx sensor?
This process can take up to 15 minutes from ignition ON (engine start).
Can a bad NOx sensor trigger DEF inducement?
Yes, if left unaddressed, it can lead to DEF inducement and engine derating.
What should I check if the new NOx sensor doesn’t work immediately?
Verify the correct cross-reference, ensure good electrical connections, and run a complete system diagnostic.
How does SPN 520373 affect the SCR system’s operation?
It can cause the system to use excessive DEF in an attempt to reduce NOx emissions, leading to inefficient operation.
Is SPN 520373 specific to certain vehicle makes or models?
No, it’s a generic code that can appear on many diesel vehicles with SCR systems, including various truck brands and some passenger vehicles.