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SPN 22 FMI 4

Engine Extended Crankcase Blow-by 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: A blow-by pressure or flow reading taken in the crankcase ventilation path on engines that monitor it. It is used to spot excessive blow-by past the rings or a restricted breather. More on SPN 22.

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

HIGH — limit use, diagnose now

High blow-by readings usually come with a derate. Check the breather system first, then test the engine; continued hard running can push out seals and worsen internal damage.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Plugged crankcase breather filter or oil separator
  3. Restricted, kinked or frozen vent/draft tube
  4. Worn or broken piston rings, or a damaged piston
  5. Air compressor or turbo leaking pressure into the crankcase
  6. Sensor, sensor port 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. Check oil level and when the breather filter was last replaced
  4. Inspect the vent hoses and draft tube for kinks, sludge and ice
  5. Verify the sensor reads near zero with the engine off and the port is clean
  6. Perform the OEM blow-by test with a manometer at the specified speed and load

Troubleshooting guides

FAQ

What does SPN 22 FMI 4 mean?

Engine Extended Crankcase Blow-by Pressure — voltage below normal or shorted low. The sensor circuit voltage is lower than it should ever be, usually near zero.

Is SPN 22 FMI 4 serious?

High blow-by readings usually come with a derate. Check the breather system first, then test the engine; continued hard running can push out seals and worsen internal damage.

What should I check first for SPN 22 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; Check oil level and when the breather filter was last replaced.