John Deere Engines SPN 174 FMI 3 Fault Code: Fuel Temperature Signal Out Of Range High
Also called Fuel Temperature Input Voltage High, Fuel Temperature Signal Out of Range High
Fuel Temperature Signal Out Of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
SPN 174 FMI 3 means the ECU sees fuel temperature input voltage that has climbed above 4.9 volts, a level corresponding to a fuel temperature colder than physically possible. This points to an open circuit or, less likely, a short to a power source in the fuel temperature sensor circuit. The engine will run in a limp-home mode using a fixed default temperature value.
Medium severity. The engine keeps running on a substituted default fuel temperature value and power is only slightly derated, so this is not an immediate shutdown situation. Still, fuel delivery compensation for temperature is disabled, so the fault should be diagnosed and fixed within the shift rather than ignored long term.
What does John Deere Engines error code SPN 174 FMI 3 mean?
SPN 174 FMI 3 is set by the John Deere engine ECU when the fuel temperature sensor circuit reports an input voltage that is out of range on the high side. The fuel temperature sensor is a thermistor, a resistor that changes value with temperature, mounted on the fuel filter base, injection pump housing, or fuel manifold depending on the engine application. As fuel gets hotter, the sensor's resistance drops and the voltage seen by the ECU drops with it. As fuel gets colder, voltage rises.
Because the circuit is built so that voltage rises as resistance to ground increases, a voltage that climbs above the sensor's high voltage specification of 4.9 volts corresponds to a temperature colder than fuel could realistically be. That is a physically impossible reading, which is exactly why the ECU flags it as a fault rather than trusting the sensor value.
When this circuit behaves that way, it almost always means the circuit has gone open somewhere. It is less likely, but possible, that the 5-volt input wire has shorted to a power source instead. Either way, the ECU can no longer trust the sensor and falls back to a fixed default temperature so the engine keeps running.
What triggers a John Deere Engines SPN 174 FMI 3 code?
The code sets when the fuel temperature input voltage exceeds the sensor's high voltage specification of 4.9 volts for OEM engine applications. That voltage level corresponds to a fuel temperature colder than is physically possible, which is what tells the ECU the signal is invalid rather than just cold fuel.
Common causes of SPN 174 FMI 3
- Dirty, damaged, or poorly positioned terminals at the fuel temperature sensor connector
- Dirty, damaged, or poorly positioned terminals at the ECU connector (described as a 30-way or 60-way connector depending on application)
- An open or short in the wiring harness between the ECU and the fuel temperature sensor, including an open in the fuel temperature ground circuit or the fuel temperature input circuit
- A failed fuel temperature sensor (bad thermistor)
- A failed ECU
How to troubleshoot John Deere Engines SPN 174 FMI 3: first checks
- Without unplugging anything yet, visually inspect the ECU connector and the fuel temperature sensor connector for contamination, corrosion, physical damage, or terminals that are pushed back or poorly seated
- Trace the wiring harness between the sensor and the ECU looking for chafe points, pinches, or heat damage that could cause an open circuit or a short to a power source
- Check the fuel temperature ground circuit and the fuel temperature input circuit for continuity, since an open in either is a listed cause
- If terminals and wiring check out, test the fuel temperature sensor itself for correct resistance response to temperature change, since a bad thermistor is a listed cause
- Use a connector adapter test kit rather than forcing probes directly into connector terminals when taking voltage measurements, since forcing probes into terminals can damage them
- If sensor and wiring both test good, suspect the ECU itself as the last step, since a bad ECU is listed as a possible cause
How the code clears
No separate clearing step is listed beyond fixing the underlying wiring, connector, sensor, or ECU problem. Once the fuel temperature input voltage returns to a normal range, the ECU should stop substituting the limp-home default value. No distinct manual reset procedure is described for this code.
Frequently asked questions
What does SPN 174 FMI 3 mean on a John Deere engine?
It means the ECU sees the fuel temperature sensor input voltage above 4.9 volts, a reading that corresponds to a fuel temperature colder than is physically possible. This usually points to an open circuit in the sensor wiring rather than an actual cold-fuel condition.
Will the engine still run with this code active?
Yes. The ECU substitutes a fixed limp-home fuel temperature value, either 40°C (104°F) while running or -20°C (-4°F) during cranking depending on the application, or in some applications a flat 90°C (194°F) default. Engine power may be slightly derated but the engine keeps operating.
Where is the fuel temperature sensor located?
Location varies by engine application. It has been documented on the base of the fuel filter, on the injection pump fuel outlet or inlet housing, and on the fuel manifold. All versions are thermistors that change resistance with fuel temperature.
Is this more likely a wiring problem or a bad sensor?
Wiring and connector issues are the more probable cause. Because the circuit is designed to show rising voltage as resistance to ground increases, an open circuit is the probable cause, with a short from the 5-volt input wire to a power source being less probable. A bad sensor or bad ECU are also listed but are further down the list.
How is SPN 174 FMI 3 different from SPN 174 FMI 16?
SPN 174 FMI 3 is a full out-of-range-high fault, triggered when voltage exceeds the 4.9 volt high specification, an impossible-low-temperature reading caused by an open circuit or short to power. SPN 174 FMI 16 covers a moderately high signal, a smaller deviation that does not cross the full out-of-range threshold. If your voltage reading is elevated but not past the hard high spec, check the FMI 16 page instead.
How is this different from SPN 174 FMI 4?
FMI 4 is the opposite failure mode, fuel temperature signal out of range low, generally caused by an open, a short to ground, or loss of sensor supply voltage that drives the input voltage down instead of up. FMI 3 is specifically a high-voltage fault caused mainly by an open circuit that lets voltage rise unexpectedly.
Can I safely probe the connectors to test this circuit myself?
Do not force test probes directly into the connector terminals, since that can damage the terminals and create a new fault. Use a proper connector adapter test kit designed for making measurements without deforming the pins.