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SPN 627 FMI 4

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

What the SPN covers: General power supply to the controller is outside the expected range or was interrupted. More on SPN 627.

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

Power interruptions cause random resets and odd faults. Fix the wiring first.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Loose ECM power connection
  3. Corroded battery terminals
  4. Faulty relay or fuse
  5. Ignition switch circuit 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. Inspect ECM power and ground connections
  4. Check fuses and relays
  5. Voltage-drop test the circuits under load

FAQ

What does SPN 627 FMI 4 mean?

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

Is SPN 627 FMI 4 serious?

Power interruptions cause random resets and odd faults. Fix the wiring first.

What should I check first for SPN 627 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; Inspect ECM power and ground connections.