P051F Positive Crankcase Ventilation Filter Restriction

Description and meaning of DTC p051f

This generic powertrain diagnostic trouble code (DTC) typically applies to many OBD-II vehicles. That may include but is not limited to vehicles from Ford, Dodge, Ram, Volvo, etc. If you have a code P051F stored in your OBD-II vehicle, it means that the powertrain control module (PCM) has detected a signal from the crankcase pressure sensor that indicates an over pressure condition exists. Air density (pressure) in the engine crankcase is monitored by the PCM using an input voltage signal from the crankcase pressure sensor. Crankcase pressure sensor input voltage is received (by the PCM) as actual units of pressure. Either kilopascal (kPa) units or inches of mercury (Hg) are used to measure crankcase pressure. The crankcase pressure sensor is typically located in or near one of the valve covers. Because the lower end of the internal combustion engine must be sealed to prevent oil leaks, a certain amount of pressure is created there. This pressure is caused by drastic changes in temperature, the vapors created by engine oil, and the rapid centrifugal motion of the crankshaft, connecting rods, etc. The positive crankcase ventilation (PCV) system uses carefully controlled intake vacuum to draw pressure from the crankcase through a specially designed valve (PCV valve) that only allows a single direction of flow. In the vast majority of vehicle applications, the PCV valve itself is responsible for filtering unwanted oil and debris and preventing it from entering the intake manifold. In this particular application, a PCV filter has been added as a precautionary measure for protecting the engine air delivery system from excess oil and debris. If the PCM detects a level of pressure from the crankcase pressure sensor that exceeds maximum parameters, a code P051F will be stored and a malfunction indicator lamp (MIL) may be illuminated.

p051f diagnostic trouble code symptoms

Symptoms of a P051F engine code may include:Engine oil leaksSmoke (steam) from underhood areaHissing (sucking) noise from engine areaDrivability issues created by a vacuum leak

DTC p051f - possible causes

Causes for this code may include:Clogged (bad) PCV filterFaulty PCV valveDefective crankcase pressure sensorOpen or shorted crankcase pressure sensor wiringPCM malfunction or PCM programming error

How to fix OBD-II diagnostic trouble code p051f

In my experience, a manual vacuum pressure gauge, a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information will be necessary when diagnosing a code P051F. A manual vacuum pressure test should be performed prior to diagnosing any excessive crankcase pressure/PCV related codes. If the engine fails to produce enough vacuum, it must be repaired before moving forward with your diagnosis. To conduct a manual vacuum pressure test, disconnect the PCV vacuum hose and attach your vacuum pressure gauge there. Your vehicle information resource should yield specifications regarding minimum engine vacuum. Check all PCV hoses for signs of cracking or breakage and make repairs as necessary. Cracked or collapsed PCV vacuum hoses may contribute to the conditions which caused the P051F to be stored. If there is sufficient vacuum on the inlet side of the PCV filter but not on the outlet side, suspect that the filter is clogged. If the engine is in good working order and there are no vacuum leaks, continue with a visual inspection of all crankcase pressure sensor wiring and connectors. Make repairs as needed. Next, I would connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. Writing this information down may aid you as your diagnosis unfolds. 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 required to proceed with your diagnosis.   Test the crankshaft pressure sensor using the DVOM With the key on and engine off (KOEO), place the DVOM on the ohms setting and follow manufacturer&rsquos procedures/specifications for testing the crankcase pressure sensor with the connector unplugged  If the sensor in question does not comply with manufacturer&rsquos specifications, it should be considered defective If the sensor does comply with manufacturer&rsquos specifications, move on to the next stepUse the DVOM to test for reference voltage (typically 5-volts) and a ground at the crankcase pressure sensor connector With the KOEO and the crankcase pressure sensor unplugged, probe the reference voltage pin of the sensor connector with the positive test lead of the DVOM Connect the negative test lead to the ground pin of the connector to test the entire circuitIf there is no reference voltage detected at the sensor connector, locate the PCM and test the corresponding circuit at the PCM connector. Use the positive test lead of the DVOMThe negative test lead should be connected to a known good ground for this testIf there is no reference voltage at the PCM connector, suspect PCM failure or a programming errorIf there is no ground at the sensor connector, use your source of vehicle information to locate the ground source and make sure that it is securely fastened to the engine block or battery If there is reference voltage and ground at the crankcase pressure sensor connector, proceed to the next stepTest crankcase pressure sensor signal circuit voltage using the DVOMWith the key on engine running (KOER) and the crankcase pressure sensor reconnected, use the positive lead of the DVOM to probe sensor signal voltage right behind the connectorThe negative test lead should again be connected to a battery groundUse the vacuum pressure gauge to obtain correct crankcase pressure and compare sensor signal voltage to the pressure-to-voltage chart in your vehicle info resourceIf crankcase pressure sensor signal voltage is incorrect, consider the sensor faultyIf crankcase pressure sensor signal voltage (at the sensor connector) reflects the correct degree of voltage, proceed to the next stepTest the crankcase pressure sensor signal circuit at the PCM connectorWith the KOER, use the DVOM positive test lead to probe the crankcase pressure sensor signal circuit at the PCM connectorThe negative test lead should be connected to a battery groundIf a correct crankcase pressure sensor signal is discovered at the sensor connector but not at the corresponding circuit of the PCM connector, suspect that there is an open circuit between the twoIf the crankcase pressure sensor and all circuits are within specifications, suspect PCM failure or a PCM programing error. Technical service bulletins (TSB) which parallel the vehicle in question (as well as the symptoms and codes stored) may help with your diagnosis

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