John Deere Engines SPN174FMI4 Fault Code: Fuel Temperature Signal Out Of Range Low
Also called Fuel Temperature Input Voltage Low, Fuel Temperature Signal Out of Range Low
Fuel Temperature Signal Out Of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN174FMI4 means the ECU sees the fuel temperature sensor's input voltage drop below its valid low range, a voltage that corresponds to an impossibly high fuel temperature. The ECU switches to a limp-home fuel temperature value and slightly derates engine power. This is usually a wiring, connector, or sensor problem, not a real over-temperature event.
Medium severity. The engine keeps running on a substituted fuel temperature value and power is only slightly reduced, so this is not an immediate shutdown risk. Still, it should be diagnosed promptly since fuel delivery adjustments for temperature are no longer accurate.
What does John Deere Engines error code SPN174FMI4 mean?
SPN174FMI4 is set by the engine's ECU when the fuel temperature sensor circuit reports a voltage that is lower than the sensor's valid operating range. Because this sensor is a thermistor, its resistance and output voltage change with fuel temperature: hotter fuel produces a lower voltage, colder fuel produces a higher voltage. When the voltage falls below the low-voltage specification, it corresponds to a fuel temperature that is physically impossible, so the ECU flags the reading as invalid rather than trusting it.
The fuel temperature sensor itself is a thermistor mounted on the fuel system, depending on the engine platform, this can be at the base of the fuel filter, on the injection pump fuel outlet or inlet housing, or on the fuel manifold. Its job is to let the ECU adjust fuel delivery for changes in fuel density caused by temperature swings.
Because the circuit is designed to interpret a voltage drop as decreasing resistance to ground, the most likely underlying cause of this fault is a grounded or shorted circuit rather than a true sensor failure.
What triggers a John Deere Engines SPN174FMI4 code?
The fault sets when the fuel temperature input voltage drops below the sensor's low voltage specification. On OEM engine applications this specification is listed as 0.1 volts in one reference and 0.3 volts in another, depending on the application; other applications use a spec found in the engine's application specifications documentation. Once tripped, the ECU substitutes a limp-home fuel temperature value, which is listed variously as 40°C (104°F), or as -20°C (-4°F) during cranking and 40°C (104°F) during running, or as 90°C (194°F) depending on the platform, and engine power may be slightly derated.
Common causes of SPN174FMI4
- Dirty, damaged, or poorly positioned terminals at the fuel temperature sensor connector
- Dirty, damaged, or poorly positioned terminals at the ECU connector (30-way or 60-way, depending on platform)
- Open or short in the wiring harness between the ECU and the fuel temperature sensor, including a short to ground in the fuel temperature input circuit
- A bad fuel temperature sensor
- A bad ECU
How to troubleshoot John Deere Engines SPN174FMI4: first checks
- Without disconnecting anything yet, visually inspect the ECU connector and the fuel temperature sensor connector for contamination, corrosion, damage, or terminals that are pushed back or poorly seated
- Inspect the wiring harness between the sensor and ECU for chafing, pinches, or exposed conductors that could short to ground
- If probing connector terminals to check voltage, use a proper connector adapter test kit rather than forcing probes into the terminals, since forcing probes can damage them and create a new fault
- Locate the fuel temperature sensor on your specific engine, it may be at the fuel filter base, the injection pump fuel inlet or outlet housing, or the fuel manifold, and check that its connector is fully seated and undamaged
- With power off, check the sensor's resistance and compare readings against the wiring for opens or shorts, and check circuit continuity to ground for an unwanted short
How the code clears
No separate clearing step is listed beyond repairing the underlying wiring, connector, or sensor problem. Once the voltage returns to a valid range and the ECU no longer sees an out-of-range low signal, the code should clear on its own after the repair; a technician should verify the fault does not return during operation.
Frequently asked questions
What does SPN174FMI4 mean on a John Deere engine?
It means the ECU detected the fuel temperature sensor's input voltage dropped below the valid low range, a voltage that corresponds to a fuel temperature that is physically impossible. The ECU treats this as an invalid signal rather than a real reading.
Can I keep running the equipment with this code active?
The engine will keep running using a substituted limp-home fuel temperature value, and power may be slightly reduced. It is not listed as an immediate shutdown condition, but the fuel delivery is no longer being properly adjusted for actual fuel temperature, so the fault should be diagnosed as soon as practical.
Where is the fuel temperature sensor located?
Location varies by engine platform. It can be at the base of the fuel filter, on the injection pump fuel outlet housing, on the injection pump fuel inlet housing, or on the fuel manifold. Check your specific engine's service information to confirm.
What is the most likely cause of this fault?
A grounded or shorted circuit is the most probable cause, since the sensor circuit is designed to see a voltage drop as decreasing resistance to ground. Bad terminals or connectors at either the sensor or the ECU, an open or short in the harness, a failed sensor, or a bad ECU can all trigger it.
What voltage triggers SPN174FMI4?
On OEM engine applications the low voltage specification is listed as 0.1 volts in one version and 0.3 volts in another, depending on the engine platform. Other applications should check the application specifications documentation for the exact threshold used on that engine.
Will this code clear itself after I fix the wiring?
No separate reset procedure is listed. Once the voltage signal returns to a valid range after repairing the connector, wiring, or sensor issue, the code should clear on its own; confirm it stays clear during normal operation.
Is this the same as an over-temperature fuel warning?
No. Despite the voltage corresponding mathematically to a temperature higher than physically possible, this fault is not a real high fuel temperature event. It indicates an electrical problem in the sensor circuit, most often a short to ground.