What is SPN 174 FMI 3 & How to Solve It?

What is SPN 174 FMI 3:

SPN 174 refers to Fuel Temperature, and FMI 3 means the voltage or reading is above the normal range.

This code indicates that fuel temperature is too high, which may cause vapor lock, injector problems, or fuel viscosity issues, affecting engine power and efficiency.

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Why This Happens

• Hot return fuel not cooling properly.
• Faulty or damaged fuel temp sensor.
• Restricted fuel cooler.
• Excessive engine load or ambient heat.
• Electrical issue with sensor circuit.

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How to Fix It

1. Inspect the fuel cooler for clogs or low coolant flow.
2. Check sensor readings vs. actual fuel temperature.
3. Replace the sensor if readings are too high while system is cool.
4. Improve fuel line routing to reduce heat soak.
5. Clear the code and monitor fuel temperature under load.

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How to Avoid It Before It Happens

1. Maintain clean and functional fuel coolers.
2. Keep fuel lines insulated and away from hot components.
3. Inspect return lines for blockages.
4. Replace temperature sensors that drift over time.

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