John Deere Engines SPN110FMI3 Fault Code: Engine Coolant Temperature Signal Out of Range High
Also called Coolant Temperature Signal Out of Range High, Engine Coolant Temperature Input Voltage High
Engine Coolant Temperature Signal Out of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 110 FMI 3 (also shown as DTC 110.03) means the engine coolant temperature sensor input voltage has gone above the ECU's high voltage specification, listed as 4.9 volts on OEM applications. That voltage corresponds to a coolant temperature colder than physically possible, so the ECU knows the reading is bad, drops into a default limp-home value, and disables high coolant temperature engine protection.
High severity. The engine itself will keep running because the ECU substitutes a default coolant temperature value, but this disables the ECU's high engine coolant temperature protection feature. That means the engine could overheat without the normal automatic protection response. Diagnose promptly rather than running on the default value for an extended period.
What does John Deere Engines error code SPN110FMI3 mean?
SPN 110 FMI 3 means the Engine Control Unit (ECU) is seeing an input voltage from the Engine Coolant Temperature (ECT) sensor circuit that is too high to be a real coolant temperature reading. The ECT sensor is a thermistor, a resistor whose resistance changes with temperature, mounted on the thermostat housing or at the rear of the cylinder head. As coolant gets hotter, the sensor's resistance drops and the input voltage to the ECU drops with it. As coolant gets colder, the voltage rises. If that voltage climbs above the sensor's high voltage specification, listed as 4.9 volts for OEM applications, it corresponds to a coolant temperature lower than what is physically possible, so the ECU flags the signal as invalid rather than trusting it.
Because the sensor circuit is designed so that voltage rises as resistance to ground increases, the most likely underlying cause is an open circuit somewhere between the sensor and the ECU. A short from the 5-volt input wire to a power source is possible but less likely.
When this code sets, the ECU substitutes a default coolant temperature value instead of using the sensor signal, and it turns off the ECU's high coolant temperature engine protection feature. That protection is what would normally warn or pull power in an overheat situation, so losing it means an actual overheating engine could go unprotected.
Common causes of SPN110FMI3
- Bad, dirty, damaged, or poorly positioned terminals or connector at the ECU (documented as either a 60-way or 30-way connector depending on application)
- Bad terminals or connector at the ECT sensor itself
- Open or short in the wiring/circuits between the ECT sensor and the ECU, including possible open in the ECT ground circuit or open in the ECT input circuit
- Bad or failed ECT sensor
- Bad ECU
How to troubleshoot John Deere Engines SPN110FMI3: first checks
- Check for a related SPN 1080 FMI 3 code. If it is present, follow that diagnostic procedure first before working SPN 110 FMI 3.
- Without disconnecting anything, visually inspect the ECU connector and the ECT sensor connector for contamination, corrosion, damage, or terminals that are not fully seated.
- Inspect the wiring harness between the ECT sensor and the ECU for chafing, pinches, or damage that could cause an open or a short to a power source.
- When probing connectors for voltage checks, use a proper connector adapter test kit rather than forcing probes into the terminals, since forcing probes can damage the terminals and create a new fault.
- Test the ECT sensor itself and its ground circuit for continuity and correct resistance behavior, since an open ground or open input circuit reads the same as a failed sensor to the ECU.
- If wiring, connectors, and the sensor all check out, suspect the ECU itself.
How the code clears
No separate clearing step is listed. Once the underlying open, short, bad connector, bad sensor, or bad ECU is repaired and the input voltage returns to a normal range, the code should stop being active. Cycling the key or clearing codes with a service tool after the repair is standard practice, but no distinct reset procedure is described here.
Frequently asked questions
What does SPN 110 FMI 3 mean on a John Deere engine?
It means the engine coolant temperature sensor circuit is sending a voltage to the ECU that is higher than the sensor's high voltage specification, listed as 4.9 volts for OEM applications. That voltage represents an impossible, too-cold coolant reading, so the ECU treats the signal as invalid.
Can I keep driving or running the machine with this code active?
The engine will keep running because the ECU substitutes a default coolant temperature value, but the ECU's high coolant temperature engine protection feature is disabled while the code is active. That means an actual overheat condition would not be caught automatically. It is best treated as a fault to diagnose soon rather than ignore.
What default temperature does the ECU use when this code is active?
Documentation varies slightly by application. Some describe the ECU defaulting to -30°C (-22°F) in start mode and 90°C (194°F) in running mode. Other versions describe a single limp-home default value of 90°C (194°F) or 95°C (203°F), and a start-mode default of 0°C (32°F) in one version. Regardless of the exact default used, the engine's actual coolant temperature is not being measured while the fault is active.
What usually causes SPN 110 FMI 3?
The most common causes are dirty, damaged, or poorly seated connectors or terminals at the ECU or at the ECT sensor, an open or short in the wiring between them, a failed ECT sensor, or in less common cases a faulty ECU. An open circuit is considered the more likely cause because of how the sensor circuit is designed.
Is there a code I should check before working on SPN 110 FMI 3?
Yes. If SPN 1080 FMI 3 is also present, that diagnostic procedure should be followed first before addressing SPN 110 FMI 3.
What tools should I use to test the connectors?
Do not force test probes into the connector terminals, as this can damage them. Use a proper connector adapter test kit designed to make measurements in the connector without damaging the terminals.
Will clearing the code make it go away permanently?
No separate clearing procedure is documented. The code should stop setting once the actual open, short, bad connector, bad sensor, or bad ECU is repaired. If the underlying wiring or connector issue is intermittent, the code can return.