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SPN 102 FMI 4

Intake Manifold #1 Pressure (Boost) — Voltage below normal or shorted low.
The sensor circuit voltage is lower than it should ever be, usually near zero.

What the SPN covers: Boost pressure in the intake manifold after the turbocharger and charge air cooler. More on SPN 102.

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

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 4 mean?

Intake Manifold #1 Pressure (Boost) — voltage below normal or shorted low. The sensor circuit voltage is lower than it should ever be, usually near zero.

Is SPN 102 FMI 4 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 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; Pressure-test the charge-air system for leaks.