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SPN 105 FMI 3

Intake Manifold #1 Temperature — Voltage above normal or shorted high.
The sensor circuit voltage is higher than it should ever be, usually pegged near the supply voltage.

What the SPN covers: Temperature of the air entering the cylinders after the charge air cooler. More on SPN 105.

What FMI 3 usually points to: Signal wire shorted to the 5 V reference or battery, an open ground, or an unplugged sensor on a pulled-up circuit. More on FMI 3.

Severity

MEDIUM — fix soon

High intake temps reduce power and can lead to a derate. Drivable with care.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Dirty or blocked charge-air cooler fins
  3. Charge-air cooler leak
  4. Fan not engaging
  5. EGR cooler problem raising intake temperature
  6. 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. Clean the CAC and radiator stack
  4. Verify fan engagement
  5. Pressure-test the CAC
  6. Compare the sensor to ambient after a cold soak

FAQ

What does SPN 105 FMI 3 mean?

Intake Manifold #1 Temperature — voltage above normal or shorted high. The sensor circuit voltage is higher than it should ever be, usually pegged near the supply voltage.

Is SPN 105 FMI 3 serious?

High intake temps reduce power and can lead to a derate. Drivable with care.

What should I check first for SPN 105 FMI 3?

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; Clean the CAC and radiator stack.