John Deere Engines SPN110FMI15 Fault Code: Engine Coolant Temperature Signal Slightly High
Also called Coolant Temperature Signal Slightly High, Engine Coolant Temperature High Least Severe
Engine Coolant Temperature Signal Slightly High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 110 FMI 15 means the ECU has detected engine coolant temperature above its warning set point, sometimes shown as DTC 110.15 or a blinking info light. It is the least severe coolant-temperature warning and triggers engine protection with a power derate, not a shutdown.
Medium severity. This is listed as the least severe coolant temperature fault and does not trigger a shutdown, only a power derate. Still, it warns of a real overheating trend and should not be ignored, since continued high coolant temperature can lead to more severe engine protection faults or engine damage.
What does John Deere Engines error code SPN110FMI15 mean?
SPN 110 FMI 15 tells you the engine control unit (ECU) has seen engine coolant temperature climb above its programmed warning threshold. The engine coolant temperature (ECT) sensor is a thermistor, a resistor that changes value with temperature, mounted on the thermostat housing or near the rear of the cylinder head. As coolant gets hotter, the ECT's resistance drops and the voltage signal sent to the ECU drops with it. The ECU reads that voltage and calculates a temperature.
This is described across different applications as the least severe coolant temperature fault, distinct from more severe overheating codes. When it sets, the ECU enables engine protection. There is no shutdown feature tied to this code. Instead, on OEM applications with the derate feature enabled, the engine reduces power by 2% per minute until it reaches either 95% of full power or, on some applications, 80% of full power, depending on the specific application configuration. Some displays will also show a blinking info light.
Because this fault can be caused either by a genuinely overheating engine or by a bad sensor/wiring problem reporting a false high reading, diagnosis has to consider both possibilities before assuming the cooling system itself is at fault.
What triggers a John Deere Engines SPN110FMI15 code?
The ECU sets SPN 110 FMI 15 when it senses engine coolant temperature above the warning set point programmed for the application. Specific thresholds given for OEM applications include above 108°C (226°F), above 100°C (212°F) for the ECT high least severe specification, and above 110°C (230°F) on another application variant. One version also notes the engine must be running for 3 minutes before this code is allowed to set.
Common causes of SPN110FMI15
- Bad terminals or connector at the ECU (dirty, damaged, or poorly positioned pins)
- Bad terminals or connector at the ECT sensor
- Open or short in the wiring harness between the ECU and ECT sensor
- Bad ECT sensor itself
- Engine actually overheating due to cooling system problems
- Internally or externally plugged radiator
- Coolant leaks
- Damaged fan shroud
- Loose fan belt
- Bad radiator cap
- Bad thermostat
- Excessively high ambient temperature
- Bad ECT sensor housing or O-ring
- Bad ECU software
- Bad ECU
How to troubleshoot John Deere Engines SPN110FMI15: first checks
- Without disconnecting anything, visually inspect the 60-way ECU connector, the ECT sensor connector, and any connectors in between for dirt, corrosion, damage, or terminals that are pushed back or poorly seated.
- Check the wiring harness between the ECU and ECT sensor for chafing, pinches, or exposed conductors that could cause an open or short circuit.
- Look over the cooling system itself: check coolant level, look for external or internal leaks, inspect the radiator for plugging (inside and out), check the fan shroud for damage, check fan belt tension, and inspect the radiator cap for a good seal.
- Confirm the thermostat is opening properly and not stuck closed or partially stuck, which can drive coolant temperature up even with everything else working.
- If the reading is at or above the specification, treat it as a real engine overheating problem and address the cooling system before returning to service.
- If the reading is significantly lower than the specification but the code is active, verify the ECT sensor input and return circuits are good with no open or short. If those circuits check out, replace the ECT sensor and retest.
How the code clears
No separate clearing step is listed beyond fixing the underlying cause. Since there is no shutdown feature tied to this code, the ECU continues to run the engine normally while under derate; once coolant temperature drops back below the warning threshold and the root cause (wiring, sensor, or actual overheating) is corrected, the derate and warning should clear on their own during normal operation.
Frequently asked questions
What does SPN 110 FMI 15 mean on a John Deere engine?
It means the ECU has detected engine coolant temperature above its warning set point. It is described as the least severe of the coolant temperature high faults and triggers engine protection with a gradual power derate rather than a shutdown.
Will SPN 110 FMI 15 shut down my engine?
No. The documentation for this code specifically states there is no shutdown feature available for it. Instead, on applications with the derate feature, power is reduced by 2% per minute until the engine reaches a reduced power level, either 95% or 80% of full power depending on the application.
Can a bad sensor cause this code instead of real overheating?
Yes. A bad ECT sensor, corroded or damaged connector terminals at the ECU or sensor, or an open or short in the wiring harness can all cause a false high coolant temperature reading. If the actual temperature reads well below the fault threshold, suspect the sensor or wiring rather than the cooling system.
What coolant temperature triggers this fault?
Depending on the application, the threshold is listed as above 108°C (226°F), above 100°C (212°F), or above 110°C (230°F). Check the application-specific derate specifications for the exact value on your engine.
How long does the engine need to run before this code can set?
One version of the diagnostic procedure notes the engine must be running for 3 minutes with the error active before the code is set.
What should I check first if I get this code?
Start with a visual inspection of the ECU and ECT sensor connectors and the wiring between them for damage, corrosion, or poor terminal fit. Then check basic cooling system items: coolant level, radiator condition, fan belt, fan shroud, radiator cap, and thermostat operation.
Is it safe to keep operating with this code active?
The engine will keep running under a gradual power derate, so it is not an immediate shutdown situation, but continuing to operate with real coolant overheating risks engine damage. Treat any temperature reading at or above the listed specification as a genuine overheating problem and address it before continued heavy use.