SPN 110 FMI 16 – Coolant Temperature High Fault Code (Symptoms, Causes & Fix)

Mar 13, 2026

The SPN 110 FMI 16 fault code is a diesel engine diagnostic trouble code indicating that the engine's coolant temperature is higher than the expected range. This code is triggered when the Engine Control Module (ECM) detects a coolant temperature reading that exceeds the predefined threshold, suggesting a potential issue with the engine's cooling system.

What SPN 110 FMI 16 Means

The SPN 110 FMI 16 fault code specifically relates to the engine coolant temperature monitoring system. It indicates that the ECM has detected a high coolant temperature condition, which could be due to a variety of mechanical or electrical issues within the cooling system. The ECM uses input from the coolant temperature sensor to monitor this parameter and will set this code if the readings are consistently above normal operating levels.

Common Causes of This Fault Code

Thermostat stuck closed
Radiator blockage or restriction
Faulty coolant temperature sensor
Low coolant level
Water pump failure
Cooling fan malfunction

Symptoms Drivers May Notice

When the SPN 110 FMI 16 fault code is active, drivers may notice symptoms such as the engine overheating warning light on the dashboard, a noticeable increase in engine temperature gauge readings, or even steam coming from the engine compartment. In severe cases, the engine may enter a derate mode to prevent damage.

How Technicians Diagnose This Fault

Diagnosing the SPN 110 FMI 16 fault code involves a systematic approach:

Start with a visual inspection of the cooling system, checking for obvious leaks or blockages in the radiator and hoses.
Verify the coolant level and top off if necessary.
Inspect the wiring harness and connectors for damage or corrosion that could affect sensor readings.
Test the thermostat operation by feeling for temperature differences across the thermostat housing.
Check the operation of the cooling fan and fan clutch to ensure they engage when needed.
Use a multimeter to test the coolant temperature sensor for proper resistance values, ensuring it is functioning correctly.
Verify ECM data using diagnostic software to confirm the sensor readings and system performance.

Common Misdiagnosis

Technicians often make mistakes such as assuming a faulty sensor without proper testing, overlooking a partially blocked radiator, ignoring intermittent cooling fan operation, or misinterpreting normal temperature fluctuations as faults.

Can You Keep Driving?

While it may be possible to continue driving with the SPN 110 FMI 16 fault code active, it is not advisable. Prolonged operation with high coolant temperatures can lead to engine damage. If the engine enters a derate or protection mode, it will limit power to prevent overheating, which can affect drivability.

Mechanic's Diagnostic Tip

Always verify the operation of the cooling fan and fan clutch under load conditions. A fan that appears to work during idle may not engage properly at higher engine loads, leading to overheating issues.

Frequently Asked Questions

What should I check first when diagnosing SPN 110 FMI 16? Start with a visual inspection of the cooling system and verify the coolant level.
Can a faulty coolant temperature sensor cause this code? Yes, a faulty sensor can provide incorrect readings, leading to the SPN 110 FMI 16 fault code.
Is it safe to drive with this fault code? It is not recommended to drive for extended periods with this fault code active, as it can lead to engine damage due to overheating.