P051BCrankcase Pressure Sensor A Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The crankcase pressure sensor measures pressure in the crankcase ventilation (PCV) against atmosphere; Ford's EcoBoost engines use it for the disconnection check P04DB, which needs a sound sensor. P051B is its plausibility check. Ford flags a zero-point deviation above 0.15 inHg (about 0.5 kPa) from ambient with the engine stopped, and in operation at low air flow a pressure above 5 inHg (about 17 kPa) or below −0.6 inHg – so Ford also reports a real excess crankcase pressure under P051B. Maserati and Alfa Romeo bulletins name blow-by valves or software.
- What you may notice
- Check engine light on
- Possibly oil leaks or oil mist (real overpressure)
- Often no change in driving
- Likely causes
- LikelySensor zero point drifting
- PossiblePCV or blow-by valve sticking, ventilation blocked or frozen (real overpressure)
- PossibleEngine module software (known false trigger)
- RareIncreased blow-by from engine wear
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.