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Crankcase Pressure Sensor | Error P051B Code

February 23, 2024 | Victor Lukasso

Modern cars come with sensors that help ensure that each part is working fine, and one of the sensors is the crankcase Pressure Sensor.

The crankcase Pressure Sensor is a Sensor that monitors the pressure of the engine oil in the crankcase. Its primary function is to monitor the engine’s health and prevent possible damage.

“Pressure” in the above context usually occurs when fuel or diesel leakage into the piston rings and then to the crankcase, increasing the pressure on the engine.

The crankcase houses the crankshaft in an internal combustion engine. It is located below the cylinders and in the engine block’s lower part.


The crankcase serves several functions, including protecting the crankshaft and other moving parts, sealing the engine to prevent oil leaks, and in some designs, serving as a pressure vessel for engine oil to help lubricate the crankshaft and other moving parts.

This article will further discuss what a crankcase Pressure Sensor does and the error codes associated with the sensor.

What is a crankcase Pressure Sensor?

A crankcase pressure sensor, also known as a PCV (positive crankcase ventilation) valve pressure sensor, is a device that measures the blow-by pressure inside the crankcase of an internal combustion engine.

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The movement of the pistons creates this pressure and can harm the engine if it is not managed correctly. The sensor helps to monitor and regulate the pressure to maintain proper engine function and performance.

The sensor records and forwards the electrical values to the PCM, which analyses the values for any inconsistency.

If the pressure of the crankcase is too low or functioning outside the preset crankcase Pressure circuit range, it throws the P051B error code to your dashboard.

What is an Error P051B Code

P051B is a generic powertrain diagnostic trouble code (DTC) for “Crankcase Pressure Sensor Circuit Range/Performance” related to the engine’s crankcase pressure system. This trouble is rare and thus often occurs in older Ford models.

This code indicates explicitly that there is an issue with the pressure sensor in the system and that it is reading a value outside the normal operating range.

This could be due to a faulty sensor, a clogged or faulty PCV valve, an issue with the wiring or connections, or a problem with the engine’s crankcase pressure system.

To diagnose and repair this issue, it is necessary to use an OBD-II scanner to retrieve the code and other diagnostic information and then perform further testing as needed.

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Error P051B is often accompanied by symptoms such as:

  • Illuminated check engine light
  • Black soot from the exhaust
  • Reduced engine performance
  • Poor gas mileage
  • Engine Oil leaks and Wastage
  • Gasket Leaks, etc.

How to Diagnose and Fix Error P051B Code

As stated earlier, you’ll need to use an OBD-II scanner to retrieve the code and other diagnostic information before performing tests and implementing fixes.

Here are the steps to diagnose and fix the error code P051B:

  1. Retrieve the code: purchase an OBD-II scanner and connect it to the vehicle’s diagnostic port to retrieve the code. This will help identify the exact reason why the code was stored.
  2. Check loose or damaged wiring connection: Inspect the connections between the ECM and the crankcase Pressure Sensor for any breaks or corrosion.
  3. Inspect the Crankcase Pressure Sensor: Also, inspect the crankcase Pressure sensor for signs of physical damage or rust. You should consider a replacement if that’s the case.
  4. Check engine oil level: Low oil level can cause excessive crankcase pressure, so verify that the oil level is correct.
  5. Check for Vacuum leaks: Check the hoses, fittings, tubes, and other components for leaks or damage, as they could also cause abnormal pressure readings if they’re not in good condition.

That’s it.

If these steps do not resolve the code P051B, it may be necessary to seek the help of a professional mechanic for further diagnosis and repair.

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What happens when crankcase pressure is low?

Low crankcase pressure often results in reduced engine performance, poor gas mileage, Illuminated check engine light, engine oil leaks, and engine damage.

Where is the crankcase pressure sensor located?

The location of the crankcase Pressure sensor can vary depending on the make and model of the vehicle. However, it is usually located close to the top of the engine near the engine’s crankcase ventilation system on the valve cover. You may find it on the intake manifold or somewhere close to the engine compartment in some vehicles. You can consult your service manual or a professional mechanic for personalized guides.

What causes engine crankcase pressure?

Engine crankcase pressure occurs due to the pressure created inside the engine block due to the up-and-down movement of the pistons inside the cylinders. This pressure is also generated by the combustion of fuel and air in the cylinders.

Suppose the pressure inside the crankcase is not managed correctly. It can result in oil leaks, thereby causing increased oil consumption, reduced engine performance, poor gas mileage, and even damaged engine components over time.

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.