Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P051B Crankcase Pressure Sensor A Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Sensor zero point drifting
PCV or blow-by valve sticking, ventilation blocked or frozen (real overpressure)
Engine module software (known false trigger)
Increased blow-by from engine wear

Symptoms

  • Check engine light on
  • Possibly oil leaks or oil mist (real overpressure)
  • Often no change in driving

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–400
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

crankcase pressure sensorsensor wiringengine control module

Related codes

P051AP051CP051DP051EP053EP04DB

References: fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov.