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SPN 22 FMI 16
Engine Extended Crankcase Blow-by Pressure — Value too high (moderately severe).
The reading is above normal at a middle warning level — more serious than FMI 15, less than FMI 0.
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 16 usually points to: A developing over-condition that often precedes a derate. More on FMI 16.
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
- Plugged crankcase breather filter or oil separator
- Restricted, kinked or frozen vent/draft tube
- Worn or broken piston rings, or a damaged piston
- Air compressor or turbo leaking pressure into the crankcase
- Sensor, sensor port or wiring fault
Checks & fixes (easiest first)
- Check oil level and when the breather filter was last replaced
- Inspect the vent hoses and draft tube for kinks, sludge and ice
- Verify the sensor reads near zero with the engine off and the port is clean
- Perform the OEM blow-by test with a manometer at the specified speed and load
Troubleshooting guides
FAQ
What does SPN 22 FMI 16 mean?
Engine Extended Crankcase Blow-by Pressure — value too high (moderately severe). The reading is above normal at a middle warning level — more serious than FMI 15, less than FMI 0.
Is SPN 22 FMI 16 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 16?
Check oil level and when the breather filter was last replaced; Inspect the vent hoses and draft tube for kinks, sludge and ice; Verify the sensor reads near zero with the engine off and the port is clean.