SPN 110 FMI 3 – Engine Coolant Outlet Temperature Circuit Failed High Fault Code (Symptoms, Causes & Fix)

Mar 13, 2026

The SPN 110 FMI 3 fault code indicates that the engine control module (ECM) has detected a high voltage condition in the engine coolant outlet temperature circuit. This diesel engine fault code suggests that the signal from the coolant temperature sensor is reading higher than expected, which can affect engine performance and cooling efficiency.

What SPN 110 FMI 3 Means

SPN 110 FMI 3 is a diagnostic trouble code that points to an issue with the engine coolant outlet temperature sensor circuit. The ECM interprets this fault as a high voltage signal from the sensor, which could be due to a variety of electrical issues such as a short to voltage, faulty sensor, or wiring problems. This condition can lead to incorrect temperature readings, potentially causing the ECM to make improper adjustments to engine operations.

Common Causes of This Fault Code

Faulty coolant temperature sensor
Short to voltage in the sensor circuit
Corroded or damaged connector pins
Wiring harness issues such as chafing or pinched wires
ECM signal processing errors

Symptoms Drivers May Notice

When the SPN 110 FMI 3 fault code is active, drivers might notice symptoms such as erratic temperature gauge readings, engine overheating warnings, or the engine running in a derated mode. These symptoms occur because the ECM may not accurately control the cooling system due to incorrect temperature data.

How Technicians Diagnose This Fault

Technicians begin diagnosing this fault by performing a visual inspection of the coolant temperature sensor and its wiring. They check for physical damage, contamination, and ensure connectors are secure and free of corrosion. Next, they verify the sensor's power supply and ground circuits using a multimeter. A voltage drop test can help identify any shorts to voltage in the circuit. Technicians will also measure the resistance of the coolant temperature sensor and compare it to manufacturer specifications. Finally, they use diagnostic software to verify ECM data and ensure it aligns with expected values.

Common Misdiagnosis

Technicians often misdiagnose this fault by assuming a mechanical issue with the cooling system without verifying the electrical circuit. Another common mistake is replacing the coolant temperature sensor without checking the wiring and connectors, or overlooking intermittent wiring issues that only occur under certain conditions.

Can You Keep Driving?

While it may be possible to continue driving with the SPN 110 FMI 3 fault code active, it is not advisable. The incorrect temperature readings can lead to engine overheating or inefficient operation, potentially triggering engine derate or protection modes. It is best to address the issue promptly to avoid further complications.

Mechanic's Diagnostic Tip

When diagnosing SPN 110 FMI 3, always start with a thorough inspection of the wiring harness and connectors. Pay close attention to areas where the harness may rub against other components, as chafing can lead to intermittent faults that are difficult to trace.

Frequently Asked Questions

Q: What tools are needed to diagnose SPN 110 FMI 3?
A: A multimeter, diagnostic software, and basic hand tools are essential for diagnosing this fault code.

Q: Can a faulty ECM cause SPN 110 FMI 3?
A: While rare, an ECM issue could cause this fault if it misinterprets the sensor signal. However, electrical issues are more common.

Q: Is it necessary to replace the coolant temperature sensor?
A: Only replace the sensor if electrical testing confirms it is faulty. Always verify the integrity of the wiring and connectors first.