Home › Codes › SPN 110 › FMI 4

SPN 110 FMI 4

Engine Coolant Temperature — 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 engine coolant, usually measured near the thermostat housing. More on SPN 110.

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

STOP — shut down if the condition is real

If the engine is truly overheating, stop and let it cool. Never open a hot radiator cap.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Low coolant level or leak
  3. Stuck thermostat
  4. Fan clutch or fan drive not engaging
  5. Plugged radiator or debris on the cooling stack
  6. Failed water pump
  7. 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. Check coolant level (engine cool)
  4. Clean debris from radiator and coolers
  5. Verify fan engagement
  6. Compare sensor reading to an infrared thermometer
  7. Pressure-test the cooling system

FAQ

What does SPN 110 FMI 4 mean?

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

Is SPN 110 FMI 4 serious?

If the engine is truly overheating, stop and let it cool. Never open a hot radiator cap.

What should I check first for SPN 110 FMI 4?

Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins; Check the reference voltage, ground and signal at the component per OEM pin-out; Check coolant level (engine cool).