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SPN 111 FMI 4

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

What the SPN covers: Coolant level in the expansion tank or radiator, from a level probe or switch. More on SPN 111.

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

HIGH — limit use, diagnose now

Low coolant can lead to overheating and head damage. Top off and find the leak before working hard.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Coolant leak (hoses, radiator, water pump, EGR cooler)
  3. Coolant level sensor dirty or failed
  4. 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 actual level when cold
  4. Look for external leaks and white exhaust smoke
  5. Clean or test the level probe
  6. Pressure-test the cooling system

FAQ

What does SPN 111 FMI 4 mean?

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

Is SPN 111 FMI 4 serious?

Low coolant can lead to overheating and head damage. Top off and find the leak before working hard.

What should I check first for SPN 111 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 actual level when cold.