Error Code P051F is defined as Positive Crankcase Ventilation Filter Restriction. This is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, particularly those made since 1996 up to present. It is particularly common among Dodge, Ford, Ram, and Volvo, though it can appear in almost all makes and models.
When Error Code P051F is stored, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a signal from the CKP sensor (crankcase pressure sensor) that indicates an overpressure condition. This sensor is usually located in or near one of the valve covers.
The pressure or air density in the engine’s crankcase is monitored by the PCM through an input voltage signal which comes from the CKP sensor. These input voltages are received as actual units of pressure, which can be either kilopascal (kPa) units or inches of mercury (Hg) unit of measurement.
To prevent oil leaks, the lower end of the internal combustion engine must be sealed, and this creates a certain amount of pressure. This pressure is caused by drastic changes in the temperature, while vapors created by the engine oil, and the rapid centrifugal motion of the crankshaft, connecting rods, etc.
The PCV (positive crankcase ventilation) system uses carefully controlled intake vacuum, through a specially designed PCV valve which only allows a single direction of flow, to draw pressure from the crankcase. For most vehicles, the PCV valve itself is responsible for filtering unwanted oil and debris and keep it from getting into the intake manifold. For this application in particular, the PCV filter was added for precautionary measures to protect the engine air delivery system from excessive oil and debris.
The PCM monitors the pressure level in the CKP sensor. If it exceeds the parameters, then the Error Code P051F will be stored.
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Engine oil leak
- Hissing (or sucking) noise coming from the engine area
- Smoke (steam) coming from underhood area
- Drivability problems caused by vacuum leak
- Bad (clogged) PCV filter
- Faulty PCV valve
- Faulty CKP sensor
- Open or shorted CKP sensor wiring
- Malfunctioning or programming error in the PCM
How to Check
Tools needed to diagnose this code include a manual vacuum pressure gauge, digital volt/ohmmeter (DVOM), a diagnostic scanner, and a reliable source of vehicle information.
Manual vacuum pressure test must be performed before diagnosing any excessive CKP or PCV related codes. If the engine is unable to produce enough of a vacuum, then it must be fixed before moving on with further diagnosis. To do a manual vacuum test, the PCV vacuum must be disconnected, then attach the vacuum pressure gauge on its spot. You can get the information about your minimum engine vacuum from your vehicle information.
Then, check all PCV hoses for any signs of damages and do the necessary repairs. Cracked or collapsed PCV vacuum hoses can contribute to this problem. If there is enough vacuum on the inlet side of the PCV filter, but not enough on the outlet side, then that means the filter is clogged.
If the engine is in good condition and there are no vacuum leaks, then continue with the visual inspection of the CKP sensor, connectors, and wirings. Repair as needed.
Then, retrieve all the codes stored in the vehicle’s memory system and their freeze frame data by connecting the scanner to the vehicle’s diagnostic port. Take note of the information, then clear the codes and take the vehicle for a test drive to see if the code comes back.
Get the right face views, connector pin-out charts, wiring diagrams, component testing procedures, and specs from your vehicle information source. You will need this information to proceed with your diagnosis.
Use the DVOM to test the CKP pressure sensor
- With KOEO (Key on and engine off), set the DVOM at ohm setting and follow manufacturer’s procedure for testing the CKP sensor with the connector unplugged
- If the CKP sensor doesn’t comply with the specifications of the manufacturer, then that means it’s defective, which must be replaced
- If the sensor complies with the specs, then move on to the next diagnosis
Use the DVOM to test the reference voltage (5V) and ground at the CKP sensor connector using
- Test the circuit by connecting the negative test lead to the connector’s negative ground pint
- If you get no reference voltage at the sensor connector, find the PCM and test the corresponding circuit at the PCM connector. Use positive test lead of the DVOM
- Connect negative test lead to a known good ground
- If there is still no reference voltage from the PCM, then suspect a failed or programming error
- If there is no ground at the sensor connector, then use your vehicle information source to find the ground source and make sure it’s fastened securely to the engine block or battery
- If there is reference voltage and ground at the CKP sensor connector, then proceed to next step
Use DVOM to rest CKP sensor signal circuit voltage
- While at KOER (Key On Engine Running) and the CKP sensor reconnected, probe sensor signal voltage right behind the connector using the positive lead of DVOM
- Again, connect the negative test lead to the battery ground
- Get the right crankcase pressure using the vacuum pressure gauge, and then compare sensor signal voltage to the pressure-to-voltage chart based on your vehicle information source
- If the CKP sensor does not correspond with the specifications of the manufacturer, then it may be faulty
- If the CKP sensor signal voltage (at sensor connector) shows the right voltage, then proceed to next step
Test the crankcase pressure sensor signal circuit through the PCM connector
- With KOER, probe the CKP sensor signal circuit at the PCM connector using DVOM positive test lead. Negative test lead must be connected to battery ground
- If there is correct CKP sensor signal at sensor connector, but not at the corresponding circuit of the PCM connector, then there must be an open circuit between the two
- If the CKP sensor and all circuits are within the specs, then the problem could be failed or programming error in the PCM
How to Fix
Depending on the diagnosis, common repairs for this code include:
- Fix or replace damaged PCV hoses
- Repair or replacement CKP sensor connectors, wirings, or other issues that cause poor electrical connection
- Repair or replacement of open or shorted CKP sensor harness
- Replacement of CKP sensor
- Replacement or reprogramming of PCM
Since Error Code P051F results from an engine oil break, then this code is considered severe and must be addressed as soon as possible.