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SPN 102 FMI 3

Intake Manifold #1 Pressure (Boost) — 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: Boost pressure in the intake manifold after the turbocharger and charge air cooler. More on SPN 102.

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

Low boost means low power and more smoke; high boost can overstress the engine. Usually drivable carefully to a shop.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Boost leak at charge-air cooler or hoses
  3. Turbo or VGT actuator problem
  4. Clogged air filter
  5. Faulty boost sensor or plugged sensor port
  6. Exhaust restriction (DPF)

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. Pressure-test the charge-air system for leaks
  4. Inspect CAC boots and clamps
  5. Check the boost sensor for oil/soot buildup
  6. Compare boost to barometric pressure with the key on, engine off
  7. Check VGT and DPF codes

FAQ

What does SPN 102 FMI 3 mean?

Intake Manifold #1 Pressure (Boost) — 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 102 FMI 3 serious?

Low boost means low power and more smoke; high boost can overstress the engine. Usually drivable carefully to a shop.

What should I check first for SPN 102 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; Pressure-test the charge-air system for leaks.