P051B Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

So your vehicle has dozens of sensors connected to  ECM (Engine Control Module),  which acts as an electronic  “brain” that monitors and adjusts engine functions to keep everything running smoothly.

The crankcase pressure sensor is responsible for providing the ECM with crankcase pressure data to maintain an optimal functioning atmosphere inside the engine crankcase.

Since engines produce an abundance of fumes during normal operation, and this means it’s critical for the ECM to have an accurate crankcase pressure value. Not only does it ensure the pressure does not get too high and damage seals and gaskets, but it’s also a critical value for recycling combustible fumes back into the engine via the PCV (Positive Crankcase Ventilation) system.

Unused combustible crankcase fumes get routed to the intake for the engine to burn away. This efficiency function improves emissions and your fuel economy.

If your crankcase pressure sensor circuit isn’t functioning correctly, not only do you sacrifice fuel economy and increased emissions, but your engine may experience gasket failure, o-ring leaks, shaft seal leaks and crankcase pressure related problems.

Code P051B Crankcase Pressure Sensor Circuit Range/Performance and related codes get activated by the ECM (Engine Control Module) when it measures one or multiple electrical values outside the desired operating from the crankcase pressure sensor.

This illuminates the check engine light, and your vehicle should be checked out in the near future.

Causes

• Your CCPS has an internal electrical issue
• ECM issues code for PCV (Positive Crankcase Ventilation) valve as defective
• Physical damage to the PCV (broken runners/tubes, disconnected, chafed lines, etc.)
• Clogged PCV system- Sludgy oil, carbon buildup, or moisture/condensation in the crankcase
• Water intrusion in the crankcase (definitely not good!) or your  engine is over-filled with oil (easily fixable issue)

Symptoms

Here’s what you can expect to see when you have a P051B DTC:

• Gas mileage is lower than usual
• Gasket leaks
• Strong smell of fuel in the exhaust and CEL (Check Engine Light) is illuminated
• Engine idles rough
• Engine oil is sludgy as opposed to free running
• Black smoke and soot from the exhaust
• High/Low internal crankcase pressure readings

Diagnosis

The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins (TSB) for known issues with the specific vehicle.

These vary by manufacturer and engine, so your automotive service technician should search by your specific make, model and trim level. Some technicians can even search TSBs by VIN number to find TSBs specific to your vehicle more rapidly.

Advanced diagnostic steps are usually vehicle specific, and finding the root cause of your P051B DTC may require manufacturer specific advanced equipment, and your technician should have manufacturer specific experience and knowledge using said equipment.

Common mistakes

Sometimes automotive service centers skip the TSB recommended diagnosis and instead replaces the sensor.

Not only does this not necessarily repair the problem, but it also runs the risk of creating a more serious and expensive issue when your vehicle blows a gasket or a crankcase seal because the pressure is too high or too low.

How serious

In the grand scheme of automotive maintenance, this fault would be considered moderate-low priority. If your CCPS fails, you don't run the risk of immediate engine failure that would render your vehicle inoperable.

You definitely need to address the problem sooner rather than later, as the long term consequences of high or low crankcase pressure can be expensive to repair.

What Repairs Can Fix A P051B DTC?

Changing the oil and ensuring it’s not overfull is the first step. It clears out any sludgy oil that may be causing the problem, and if your crankcase was over full it will resolve that issue, too.

Replacing the CCPS is sometimes the best fix, but you want to make sure a certified technician checks out your crankcase for damage or leaks before you replace just the sensor and it's fixed.

Check out the wiring harness on the CCPS, and replace any hardened or cracked wiring kit that could be causing sensor faults or inaccurate readings.

Related Codes

• P051A - Crankcase Pressure Sensor Circuit
• P051C - Crankcase Pressure Sensor Circuit Low
• P051D - Crankcase Pressure Sensor Circuit High
• P051E - Crankcase Pressure Sensor Circuit Intermittent/Erratic

Conclusion

A P051B DTC is no reason to panic, but you should take your vehicle in to an authorized automotive service center as soon as you can.

Hopefully you’re just overdue for an oil change or the sensor and wiring harness have failed. 

If it’s more complicated, at least you will have addressed the issue before it caused severe and expensive engine damage.