John Deere Engines SPN 174 FMI 4 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 2026-07-21
TL;DR
SPN174FMI4 sets when the fuel temperature sensor input voltage drops below the ECU's low voltage specification, a level that corresponds to a fuel temperature hotter than physically possible. This points to a short to ground in the signal circuit or a grounded connector. The ECU falls back to a limp-home fuel temperature value and may slightly derate engine power.
Medium severity. The engine keeps running on a limp-home fuel temperature value, so this is not an immediate shutdown issue, but fuel delivery adjustments for fuel density are lost, which can affect performance and, over time, injection accuracy. Diagnose within the shift rather than ignoring it.
What does John Deere Engines error code SPN 174 FMI 4 mean?
SPN174FMI4 means the ECU has detected that the fuel temperature sensor's input voltage has dropped below its normal low limit. The fuel temperature sensor is a thermistor, a resistor that changes resistance with temperature, mounted on the fuel filter base, injection pump fuel outlet or inlet housing, or fuel manifold depending on the engine application. As fuel gets hotter, the sensor's resistance drops and so does the input voltage seen by the ECU. As fuel gets colder, resistance and voltage rise.
Because the circuit works this way, a very low voltage reading corresponds to a fuel temperature that is hotter than physically possible. The ECU knows this isn't a real reading, so it treats the circuit as faulty. Since the circuit is designed to show falling voltage as resistance to ground decreases, a voltage this low almost always means something is pulling the signal wire down to ground, either through a short in the harness or a grounded connector.
When SPN174FMI4 sets, the ECU substitutes a fixed limp-home fuel temperature value instead of the real sensor reading. Different applications use different limp-home values: some use 40°C (104°F) at all times, others use -20°C (-4°F) during cranking and 40°C (104°F) while running, and others use 90°C (194°F). In every case, the ECU can no longer adjust fuel delivery for actual fuel density changes caused by real fuel temperature, and engine power may be slightly derated as a result.
What triggers a John Deere Engines SPN 174 FMI 4 code?
The code sets when fuel temperature input voltage drops below the sensor's low voltage specification. For OEM engine applications this threshold is listed as 0.1 volts in one application and 0.3 volts in another, depending on the specific engine and control unit. For other applications, the low voltage specification is defined in the application-specific specifications section for that engine, not given here. Once voltage falls below the applicable threshold, the corresponding calculated fuel temperature would be higher than what is physically possible, so the ECU flags the circuit rather than trusting the reading.
Common causes of SPN 174 FMI 4
- Bad, dirty, damaged, or poorly positioned terminals or connector pins at the fuel temperature sensor connector
- Bad terminals or connector pins at the ECU connector (referenced as the 30-way or 60-way ECU connector depending on application)
- An open or short in the wiring harness between the ECU and the fuel temperature sensor, most likely a short to ground in the fuel temperature input circuit given the low-voltage failure mode
- A bad fuel temperature sensor (internal short within the thermistor itself)
- A bad ECU, listed as a possible cause after the wiring and sensor have been ruled out
How to troubleshoot John Deere Engines SPN 174 FMI 4: first checks
- , turn the key off and, without disconnecting any connectors, 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 ECU and the fuel temperature sensor for chafe points, pinches, or damaged insulation that could let the signal wire touch a grounded surface
- When probing connectors is necessary, 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
- Check for a short to ground in the fuel temperature input circuit using a meter with the harness disconnected from the sensor, since this failure mode points toward low resistance to ground rather than an open circuit
- If wiring and connectors check out, test the fuel temperature sensor itself for an internal short before condemning the ECU
How the code clears
No separate clearing step is listed for this code beyond correcting the root cause. Repair the connector, harness, or sensor problem identified during diagnosis, then clear the code and verify it does not reset during a drive or work cycle. If the fault returns immediately after clearing, the short to ground is still present in the circuit or sensor.
Frequently asked questions
What does SPN174FMI4 mean on a John Deere engine?
It means the fuel temperature sensor's input voltage has dropped below the ECU's low voltage specification, a level that corresponds to a fuel temperature hotter than what is physically possible. The ECU treats this as a faulty circuit rather than a real reading.
Can I keep operating the machine with this code active?
The engine will keep running because the ECU substitutes a limp-home fuel temperature value, but engine power may be slightly derated and fuel delivery is no longer adjusted for actual fuel density changes. It's fine to finish a task, but the fault should be diagnosed and fixed rather than left active long term.
What is the fuel temperature sensor and where is it located?
It's a thermistor, a temperature sensitive resistor, that measures fuel temperature so the ECU can adjust fuel delivery for fuel density changes. Depending on the engine, it's mounted on the fuel filter base, the injection pump fuel outlet or inlet housing, or the fuel manifold.
What is the most likely cause of a fuel temperature signal low code?
Because the circuit reads falling voltage as decreasing resistance to ground, the most probable cause is low resistance to ground, meaning a short to ground somewhere in the signal circuit or a grounded connector. Bad terminals, sensor connector issues, or a shorted sensor are the other common causes.
How is SPN174FMI4 different from SPN174FMI16 or SPN174FMI3?
SPN174FMI4 is the low voltage, out of range low fault, caused by a short to ground or open circuit issue that pulls the signal voltage down below the low specification. SPN174FMI3 (Fuel Temperature Signal Out Of Range High) and SPN174FMI16 (Fuel Temperature Signal Moderately High) describe the opposite direction, where input voltage is too high, typically pointing to a different set of wiring or sensor problems. If your voltage reading is high rather than low, check those codes instead.
What voltage threshold triggers this code?
It depends on the application. Some OEM engine applications list the low fuel temperature input voltage specification as 0.1 volts, others list it as 0.3 volts. For other applications, the exact threshold is defined in the engine's specific application specifications rather than being a single universal number.
Do I need special tools to test the connectors?
Yes, it's recommended to use a proper connector adapter test kit to probe connector terminals rather than forcing test probes directly into them. Forcing probes into the terminals can damage them and create a new intermittent connection problem.