What is SPN 790 FMI 5:
SPN 790 FMI 5 indicates a low voltage condition in the Engine Fan Clutch Circuit. The fan clutch is electrically controlled and engages or disengages the engine cooling fan based on engine temperature and system demands. FMI 5 means the system is detecting less voltage than expected, which could prevent the fan from engaging properly, risking overheating.
Why This Happens
- Loose or corroded wiring to the fan clutch.
- Failing fan clutch solenoid or actuator.
- Faulty relay or blown fuse in the fan clutch circuit.
- Poor ground connection.
- ECM not delivering proper voltage due to internal fault.
How to Fix It
- Inspect wiring and connectors for damage or corrosion.
- Test the voltage at the fan clutch connector with ignition on.
- Check the fuse and relay for the fan clutch control.
- Test the resistance of the fan clutch coil; replace if out of spec.
- Clear the code and monitor fan operation after repair.
How to Avoid It Before It Happens
- Regularly inspect cooling system electrical components.
- Clean and protect all connectors from moisture and dirt.
- Replace fan clutches at recommended service intervals.
- Perform diagnostic checks if fan operation becomes erratic.
- Ensure relays and fuses are properly rated and securely seated.
- Use Clue’s Preventive Maintenance to regularly inspect the engine fan clutch system, ensuring wiring, relays, and fuses are functioning properly to prevent overheating.
