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SPN 174 FMI 4

Engine Fuel Temperature 1 — Voltage below normal or shorted low.
The sensor circuit voltage is lower than it should ever be, usually near zero.

What the SPN covers: Temperature of the fuel in the injection system. The engine computer uses it to correct fueling and may derate to protect the pump and injectors when fuel runs hot. More on SPN 174.

What FMI 4 usually points to: Signal wire shorted to ground, a lost 5 V reference, or an open signal wire on a pulled-down circuit. More on FMI 4.

Severity

MEDIUM — fix soon

Hot fuel lowers power and can damage the pump and injectors. Usually drivable carefully, but find out why it's hot.

Likely causes

1. Wiring or connector fault in this circuit (most common for electrical FMIs)
2. Running with a low tank in hot weather (little fuel to absorb return heat)
3. Restricted or missing fuel cooler airflow
4. High return flow from a leaking injector, relief valve or pump
5. Fuel temperature sensor or wiring fault

Checks & fixes (easiest first)

1. Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins
2. Check the reference voltage, ground and signal at the component per OEM pin-out
3. Fill the tank and recheck the reading
4. Inspect the fuel cooler (if fitted) for debris and damage
5. Measure injector and pump return flow per OEM
6. Compare the sensor with an infrared reading and check its circuit

Troubleshooting guides

• Low fuel rail pressure and air in the fuel: check the supply side first

FAQ