Error Code P051C is defined as Crankcase Pressure Sensor Circuit Low. 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 usually appears among Dodge, Ford, Fiat, Jeep, Nissan,  and Ram, among others. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) observes a lot of sensors, and adjust them accordingly to keep the engine in running condition. One of the many sensors is the CKP sensor or crankcase pressure sensor, which is responsible for providing PCM with the crankcase pressure values to keep a healthy atmosphere within the engine.

The engine has an abundance of fumes inside, especially when it’s running. Thus, it’s extremely important for the PCM to have an accurate crankcase pressure value to ensure the pressure does not get too high and possibly cause damage to the gaskets and seals. It does, however, require a good pressure value to keep the recycling of burnable fumes right back to the engine through the Positive Crankcase Ventilation (PCV) system.

Any unused fumes that can be burned are routed right into the intake for the engine to burn, a process that improves fuel efficiency and minimizing harmful emissions. This means it plays an extremely important role in the engine and the PCM.

Error Code P051C is set when the PCM determines that one or multiple electrical values work outside the desired range within the CKP sensor circuit, specifically when there is low voltage condition within the CKP sensor circuit.

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Common Symptoms

As with other error codes, this code activates the Check Engine light and stores the code to the vehicle’s memory system. Other common symptoms include:

  • Leaking gasket
  • Fuel smell
  • Poor engine performance
  • Increase in fuel consumption
  • Engine smokes black spot
  • Sludge in oil
  • High or low internal crankcase pressure

Possible Causes

Multiple factors lead to this problem, such as:

  • Electrical problem with the sensor
  • Defective crankcase pressure sensor
  • Defective PCV valve
  • Clogged PCV system
  • Disconnected or chafed lines, broken runners or tubes, etc. in the PCV valve
  • Sludgy oil
  • Engine over-filled with oil
  • Water intrusion
  • PCM problem

How to Check

A good starting point to diagnose this code is always checking with the TSB (technical service bulletins) for the specific model of the vehicle. Manufacturers provide step-by-step guides to address most problems.

Next, proceed with checking the oil. Open the engine’s oil cap and check for any signs of sludge build-up. Sludge can be caused by lack of oil change or not following the right oil change intervals. The rule of thumb is that conventional oil must be replaced every 5,000 km, while synthetic oil can be replaced around 8,000 to 10,000 km. Obviously, this varies from one oil manufacturer to another.

With that said, a PCV issue can also cause moisture into the system, which can also lead to sludge. Either way, ensure that oil is full and clean. Also, make sure you avoid overfilling the engine with oil, and never start the engine when this happens.

Then, use the vehicle’s service manual and follow its instructions in testing the sensors. This usually means using a multimeter and testing different value between pins. Take note and compare your findings to the specifications set by the vehicle’s manufacturer. If it’s outside the specs, then that means the crankcase pressure sensor must be replaced.

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Because crankcase pressure sensor is usually mounted right on the engine block (crankcase), harnesses and wires are exposed to the crevices with extreme temperature (i.e., the exhaust manifold). Take note of these when checking the circuits and sensors. Looks for any cracked or hardened wires or moisture in the harness.

How to Fix

  • Oil change; Ensure the oil is full and clean
  • Replacement of the crankcase pressure sensor
  • Repair or replace cracked or hardened wires in the harness and wires of the crankcase pressure sensor

Though this code doesn’t pose an immediate threat to your safety and performance of the vehicle, it can lead to more serious problems if left unchecked. Thus, it should still be addressed soon rather than later.