Technical Description of OBD-II Trouble Code
Restriction in Positive Crankcase Ventilation Filter
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is applicable to various OBD-II vehicles, including Ford, Dodge, Ram, Volvo, etc.
If your OBD-II vehicle has a stored code P051F, it means that the powertrain control module (PCM) has detected a signal from the crankcase pressure sensor indicating the presence of an over pressure condition.
The PCM monitors the air density (pressure) in the engine crankcase using an input voltage signal from the crankcase pressure sensor. The input voltage signal is received by the PCM as actual units of pressure, measured in kilopascal (kPa) or inches of mercury (Hg). The crankcase pressure sensor is typically located in or near one of the valve covers.
Due to the need to prevent oil leaks, the lower end of the internal combustion engine is sealed, resulting in the creation of a certain amount of pressure. This pressure is caused by temperature changes, engine oil vapors, and the rapid motion of the crankshaft and connecting rods.
The positive crankcase ventilation (PCV) system utilizes controlled intake vacuum to draw pressure from the crankcase through a specially designed valve (PCV valve) that allows flow in only one direction. In most vehicle applications, the PCV valve is responsible for filtering unwanted oil and debris, preventing them from entering the intake manifold. In this specific application, a PCV filter has been added as a precautionary measure to protect the engine air delivery system from excessive oil and debris.
If the PCM detects a level of pressure from the crankcase pressure sensor that exceeds the maximum parameters, it will store a code P051F and may illuminate the malfunction indicator lamp (MIL).
Photo of a PCV valve, one component of the system:
What is the severity of this DTC?
Excessive crankcase pressure may lead to engine oil leaks. A code P051F should be considered severe and addressed accordingly.
What are some of the symptoms of the code?
Symptoms of a P051F engine code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
Photo example of a crankcase pressure sensor:
What are some P051F troubleshooting steps?
In my experience, diagnosing a code P051F requires a manual vacuum pressure gauge, a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.
Prior to diagnosing any excessive crankcase pressure/PCV related codes, perform a manual vacuum pressure test. If the engine fails to produce sufficient vacuum, it must be repaired before proceeding with the diagnosis. To conduct a manual vacuum pressure test, disconnect the PCV vacuum hose and attach the vacuum pressure gauge. Refer to your vehicle information resource for specifications regarding minimum engine vacuum.
Inspect all PCV hoses for signs of cracking or breakage and make necessary repairs. Cracked or collapsed PCV vacuum hoses may contribute to the conditions that caused the P051F code to be stored. If there is sufficient vacuum on the inlet side of the PCV filter but not on the outlet side, suspect a clogged filter.
If the engine is in good working order and there are no vacuum leaks, visually inspect all crankcase pressure sensor wiring and connectors. Make repairs as needed.
Next, connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. Write down this information to aid in the diagnosis. After that, clear the codes and test-drive the vehicle to see if the code is reset.
Utilize your vehicle information resource to obtain connector face views, wiring diagrams, connector pin-out charts, component testing procedures, and specifications. All this information will be necessary to proceed with the diagnosis.
Test the crankcase pressure sensor using the DVOM
Use the DVOM to test for reference voltage (typically 5-volts) and a ground at the crankcase pressure sensor connector
Test the crankcase pressure sensor signal circuit voltage using the DVOM
Test the crankcase pressure sensor signal circuit at the PCM connector
If the crankcase pressure sensor and all circuits are within specifications, suspect PCM failure or a PCM programming error.
