SPN 101 — Engine Crankcase Pressure
System: Crankcase ventilation
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.
Can I keep running it?
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
- Plugged crankcase ventilation (breather) filter — the most common cause
- Pinched, plugged or frozen vent tube, separator drain or check valve
- Ice or moisture in the sensor port after cold starts below freezing
- Excessive blow-by from worn or broken rings
- Air compressor or turbo seals pressurising the crankcase
- Failed sensor or wiring
Checks & fixes (easiest first)
- Replace the crankcase breather filter if it is due or unknown
- Follow the vent path for kinks, sludge, a stuck check valve or ice
- Pull the sensor and inspect the port for water, ice or sludge; verify near-zero reading engine-off
- Isolate the air compressor and watch for a change in pressure
- Do a proper blow-by test before suspecting rings
Common FMIs with SPN 101
- SPN 101 FMI 0Value too high (most severe)
- SPN 101 FMI 2Data erratic, intermittent, or incorrect
- SPN 101 FMI 3Voltage above normal or shorted high
- SPN 101 FMI 4Voltage below normal or shorted low
- SPN 101 FMI 16Value too high (moderately severe)
Related codes
- SPN 22Engine Extended Crankcase Blow-by Pressure
- SPN 100Engine Oil Pressure
- SPN 102Intake Manifold #1 Pressure (Boost)
Troubleshooting guides
FAQ
What does SPN 101 mean?
SPN 101 is Engine Crankcase Pressure. 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.
Can I keep running with SPN 101?
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 causes SPN 101?
Plugged crankcase ventilation (breather) filter — the most common cause; Pinched, plugged or frozen vent tube, separator drain or check valve; Ice or moisture in the sensor port after cold starts below freezing; Excessive blow-by from worn or broken rings; Air compressor or turbo seals pressurising the crankcase; Failed sensor or wiring.