What is SPN 84 FMI 2 & How to Solve It?

What is SPN 84 FMI 2:

SPN 84 FMI 2 indicates a fault with the Engine Speed Sensor Circuit – Signal Too Low. This means the engine control module (ECM) is receiving a weaker than expected signal from the engine speed sensor, which is critical for monitoring engine RPM and managing fuel injection and ignition timing.

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Why This Happens

Common causes include:

• Faulty or failing engine speed sensor.
  
• Damaged, loose, or corroded wiring/connectors in the sensor circuit.
  
• Interference from nearby electrical components.
  
• Mechanical issues affecting sensor alignment or placement.
  
• Faulty ECM or software glitches.
  
  

How to Fix It

To resolve this fault:

1. Inspect the engine speed sensor for damage or misalignment.
   
2. Check wiring and connectors for corrosion, damage, or looseness.
   
3. Test the sensor signal output and replace if faulty.
   
4. Repair or replace damaged wiring or connectors.
   
5. Clear the fault code and verify engine RPM readings.
   
   

How to Avoid It Before It Happens

Prevent this fault by:

• Regularly inspecting the engine speed sensor and wiring.
  
• Keeping sensor mounting points clean and secure.
  
• Avoiding exposure to excessive heat or electromagnetic interference.
• Use Clue’s Construction Equipment Tracking to monitor the engine speed sensor’s performance in real-time, ensuring any issues with signal strength or sensor alignment are detected early.