What is SPN 5394 FMI 5 & How to Solve It?

What is SPN 5394 FMI 5:

SPN 5394 FMI 5 indicates a fault in the Selective Catalytic Reduction (SCR) Reactor Temperature Sensor Circuit, where the sensor signal is below the normal operating range or indicates an open circuit. This affects the engine’s ability to monitor and control the SCR system properly, potentially impacting emissions performance.

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Why This Happens

• Faulty SCR reactor temperature sensor.
  
• Damaged, broken, or corroded wiring or connectors in the sensor circuit.
  
• Open circuit or wiring harness damage.
  
• Malfunctioning SCR reactor unit.
  
• Engine control module fault.
  
  

How to Fix It

1. Inspect the SCR reactor temperature sensor wiring and connectors for damage or corrosion.
   
2. Test the temperature sensor for correct resistance and signal output.
   
3. Repair or replace any damaged wiring or connectors.
   
4. Replace the SCR reactor temperature sensor if faulty.
   
5. Verify SCR reactor unit and engine control module operation.
   
6. Clear the fault code and confirm the repair.
   
   

How to Avoid It Before It Happens

• Regularly inspect and maintain the SCR reactor temperature sensor and wiring.
  
• Protect wiring from moisture and physical damage.
  
• Follow scheduled maintenance for the SCR system.
  
• Perform routine diagnostic checks to detect early sensor or wiring issues.
• Preventive maintenance via construction software is the good practice to tackle.