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SPN 108 FMI 4

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

What the SPN covers: Outside air pressure, used to correct fueling and boost for altitude. More on SPN 108.

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

LOW — usually OK to keep running

Usually a minor drivability issue, but get it fixed so boost and fueling stay accurate.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Faulty barometric sensor (often inside the ECM)
  3. Wiring fault on external sensors
  4. ECM internal 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. Compare reading to local barometric pressure
  4. Inspect wiring on external sensors
  5. Check for ECM supply voltage codes

FAQ

What does SPN 108 FMI 4 mean?

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

Is SPN 108 FMI 4 serious?

Usually a minor drivability issue, but get it fixed so boost and fueling stay accurate.

What should I check first for SPN 108 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; Compare reading to local barometric pressure.