What is SPN 789 FMI 9 & How to Solve It?

What is SPN 789 FMI 9:

SPN 789 refers to the Engine Fan Clutch, and FMI 9 indicates the signal is abnormal or inconsistent.

This fault typically reflects delayed or mismatched fan clutch response, risking engine overheating.

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Why This Happens

• Faulty fan clutch solenoid.
  
• Signal wire intermittent or misconnected.
  
• ECM sending irregular activation commands.
  
• Fan clutch failing mechanically under load.
  

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How to Fix It

1. Inspect fan clutch and harness for signs of damage.
   
2. Use diagnostics to test fan engagement signal.
   
3. Replace fan clutch if signal is fine but clutch fails to engage.
   
4. Repair or replace wiring if signal is intermittent.
   
5. Clear the code and test fan response under engine load.
   

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How to Avoid It Before It Happens

1. Monitor fan activation times via diagnostics.
   
2. Replace clutches at their rated life interval.
   
3. Protect solenoid wiring from debris and heat.
   
4. Track operating temperature trends to catch issues early.