What is SPN 789 FMI 10 & How to Solve It?

What is SPN 789 FMI 10:

SPN 789 refers to the Engine Fan Clutch Control, and FMI 10 indicates that the circuit is functioning abnormally but not yet failed.

This code typically appears when the ECM detects that the fan clutch is not engaging or disengaging as expected, which can affect engine cooling and performance.

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Why This Happens

• Fan clutch solenoid operating outside expected range.
  
• Poor or loose electrical connection at the fan clutch.
  
• Worn clutch failing to fully engage or disengage.
  
• ECM not sending consistent signal to the fan control.
  
• Excessive resistance in the wiring harness.
  
  

How to Fix It

1. Inspect the fan clutch wiring and connector for damage or corrosion.
   
2. Test the fan clutch solenoid for correct resistance.
   
3. Command fan engagement using diagnostics and observe behavior.
   
4. Replace the fan clutch if movement or signal is inconsistent.
   
5. Clear the code and monitor fan performance during warm-up and under load.
   
   

How to Avoid It Before It Happens

1. Inspect fan clutch and connectors during every service interval.
   
2. Replace worn clutches before summer or high-load seasons.
   
3. Keep wiring harnesses secured and away from moving or hot parts.
   
4. Monitor fan engagement times using diagnostic tools.