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SPN 101 FMI 3

Engine Crankcase Pressure — 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: Gas pressure inside the crankcase, usually measured at or near the crankcase ventilation (CCV) filter. Rising pressure means the breather path is restricted or more gas is entering the crankcase than it can vent. More on SPN 101.

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

HIGH — limit use, diagnose now

Many engines derate on high crankcase pressure and some shut down. Short, light running to a shop is usually OK if the oil level is right and oil isn't being pushed out.

Likely causes

  1. Wiring or connector fault in this circuit (most common for electrical FMIs)
  2. Plugged crankcase ventilation (breather) filter — the most common cause
  3. Pinched, plugged or frozen vent tube, separator drain or check valve
  4. Ice or moisture in the sensor port after cold starts below freezing
  5. Excessive blow-by from worn or broken rings
  6. Air compressor or turbo seals pressurising the crankcase
  7. Failed sensor or wiring

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. Replace the crankcase breather filter if it is due or unknown
  4. Follow the vent path for kinks, sludge, a stuck check valve or ice
  5. Pull the sensor and inspect the port for water, ice or sludge; verify near-zero reading engine-off
  6. Isolate the air compressor and watch for a change in pressure
  7. Do a proper blow-by test before suspecting rings

Troubleshooting guides

FAQ

What does SPN 101 FMI 3 mean?

Engine Crankcase Pressure — 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 101 FMI 3 serious?

Many engines derate on high crankcase pressure and some shut down. Short, light running to a shop is usually OK if the oil level is right and oil isn't being pushed out.

What should I check first for SPN 101 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; Replace the crankcase breather filter if it is due or unknown.