What does it mean?
This is a generic diagnostic trouble code (DTC) for the powertrain and generally applies to OBD-II vehicles. Vehicle makes may include, but are not limited to, Ford, Dodge, Ram, Jeep, Fiat, Nissan, etc.
Among the countless sensors that the ECM (Engine Control Module) must monitor and adjust to keep your engine running, the crankcase pressure sensor is responsible for providing the ECM with crankcase pressure values to maintain a healthy atmosphere inside.
As you can imagine, there is an abundance of fumes inside the engine, especially during operation, so it is very important for the ECM to have an accurate crankcase pressure reading. It needs this not only to ensure that the pressure is not too high and potentially damage gaskets and seals, but it also requires this value to recycle these combustible fumes back into the engine via the PCV (Positive Crankcase Ventilation) system.
Unused combustible crankcase vapors are routed into the intake for the engine to burn. This, in turn, collectively improves emissions and your fuel economy. That said, it certainly serves a valuable purpose for the engine and ECM, so be sure to address any issues accordingly here. As mentioned, with this fault, you may be susceptible to gasket failure, O-ring leaks, shaft seal leaks, etc. As the sensor’s name implies, it is most often mounted on the crankcase.
Code P051B Crankcase Pressure Sensor Circuit Range/Performance and related codes are triggered by the ECM (Engine Control Module) when it detects one or more electrical values operating outside the desired range in the crankcase pressure sensor circuit.
When your instrument cluster illuminates with the P051B Crankcase Pressure Sensor Circuit Range/Performance code, the ECM (Engine Control Module) has detected an out-of-range condition or a general performance fault in the crankcase pressure sensor circuit.
An example of a crankcase pressure sensor (this one for a Cummins engine):
How severe is this DTC?
I would say that, in the grand scheme of things, this fault would be considered moderate to low severity. Basically, if it fails, you are not at risk of immediate drastic additional damage. I say this to emphasize the fact that it still needs to be addressed as soon as possible. Earlier, I mentioned some of the potential problems if neglected, so keep those in mind.
What are some of the symptoms of the code?
Symptoms of a P051B diagnostic trouble code may include:
Reduced fuel economy
Leaking gaskets
Fuel smell
CEL (Check Engine Light) illuminated
Engine running abnormally
Sludge in the oil
Engine emitting black soot smoke
High/Low internal crankcase pressures
What are some common causes of the code?
Causes
of this P051B engine code may include:
Faulty crankcase pressure sensor
Internal electrical issue within the sensor
ECM problem
Faulty PCV (Positive Crankcase Ventilation) valve
PCV system issue (cracked runners/tubes, disconnected lines, chafed lines, etc.)
Clogged PCV system
Sludgy oil (presence of moisture)
Water intrusion
Engine overfilled with oil
What are the diagnostic and troubleshooting steps for P051B?
The first step in the troubleshooting process for any malfunction is to check the Technical Service Bulletins (TSBs) for known issues with the specific vehicle.
For example, we are aware of a known issue with some Ford EcoBoost vehicles and some Dodge/Ram vehicles that have TSBs applicable to this DTC and/or related codes.
Advanced diagnostic steps become very vehicle-specific and may require the appropriate advanced equipment and knowledge to perform accurately. We include the basic steps below but refer to a repair guide specific to your vehicle’s year/make/model/powertrain for vehicle-specific steps.
Basic Step #1
First thing, for this fault, I would open the oil cap on top of the engine (location varies) to inspect for any obvious signs of sludge buildup. Sludge can be caused by something as simple as a lack of oil changes or using intervals longer than recommended. Speaking personally here, for conventional oil, I don’t go beyond 5,000 km. For synthetics, I go about 8,000 km, sometimes 10,000 km. This varies by manufacturer; that said, from experience, I have seen manufacturers set longer intervals than are generally recommended for many different reasons. That being said, I remain cautious and encourage you to do the same. A PCV (Positive Crankcase Ventilation) system issue can also allow moisture into the system and cause sludge. In any case, ensure your oil is clean and at the proper level.
NOTE: Be careful not to overfill the engine with oil. Do not start the engine if this has occurred; drain the oil to bring the level back to an acceptable range.
Basic Step #2
Test the sensor according to the manufacturer-specific desired values from your service manual. This typically involves using your multimeter and testing different values between the pins. Record and compare the results to the specifications for your make and model. If anything is out of specification, the crankcase pressure sensor should be replaced.
Basic Step #3
Since crankcase pressure sensors are usually mounted directly on the engine block, the involved harnesses and wires are routed through crevices and around areas of extreme temperatures (e.g., the exhaust manifold). Be aware of this when visually inspecting the sensor and its circuits. Given that these wires and harnesses are exposed to the elements, inspect for hardened/cracked wires or moisture in the harness.
NOTE: The connector must be firmly connected and free of any oil residue.