P051B code meaning
Crankcase Pressure Sensor A Circuit Range/Performance
Powertrain system Generic code P05xx codes Check engine light
What P051B means
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.
P051B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P051B
- Check engine light on
- Possibly oil leaks or oil mist (real overpressure)
- Often no change in driving
Common causes of P051B
- Most likelySensor zero point drifting
- PossiblePCV or blow-by valve sticking, ventilation blocked or frozen (real overpressure)
- PossibleEngine module software (known false trigger)
- Less likelyIncreased blow-by from engine wear
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Crankcase pressure sensorSensor wiringEngine control module
What each part of P051B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 1B | The exact fault in that area. |
What to do next
- Note P051B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P051B
What does P051B mean?
P051B means "Crankcase Pressure Sensor A Circuit Range/Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P051B?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P051B fail an emissions test?
Yes, it can. P051B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P051B to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P051B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.