What is SPN 3515 & How to Solve It?

What is SPN 3515:

SPN 3515 refers to a fault in the Aftertreatment Diesel Exhaust Fluid (DEF) Line Heater 2. This line heater prevents DEF from freezing inside the supply lines in cold conditions. When this code appears, it usually means that Line Heater 2 is not functioning properly—either due to an open circuit, internal failure, or incorrect resistance reading—leading to potential DEF flow issues and eventual derate if not resolved.

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Why This Happens

• Failed or degraded DEF line heater element.
  
• Open circuit or broken wiring to heater 2.
  
• Corroded or loose electrical connectors.
  
• Faulty relay or fuse for the line heater circuit.
  
• Malfunction in the Aftertreatment Control Module (ACM).
  
  

How to Fix It

1. Inspect DEF Line Heater 2 wiring and connector for damage or corrosion.
   
2. Check the fuse and relay related to the DEF heater system.
   
3. Test heater resistance using a multimeter; replace if out of spec.
   
4. Verify power is reaching the heater during operation.
   
5. Replace DEF Line Heater 2 if confirmed faulty and clear the fault code.
   
   

How to Avoid It Before It Happens

• Inspect DEF system heaters and wiring during routine service.
  
• Protect connectors from moisture and road debris.
  
• Use winter-grade DEF and keep it properly stored.
  
• Replace heater components at manufacturer-recommended intervals.
  
• Perform seasonal diagnostic checks, especially before winter use.
• Leverage Clue’s Equipment Tracking to monitor the performance of DEF Line Heater 2 in real-time and detect potential issues before they affect the system.