Bad PCV Valve Symptoms and How to Test the PCV Valve Yourself

What is a PCV valve?

PCV valve means positive crankcase ventilation. It is designed in a one-way format, usually attached to the valve cover, intake manifold, or engine block, depending on the engine design. However, 90% of PCV valves are found on a rubber grommet on the engine valve cover. The purpose of the PCV valve is to eliminate emissions from the crankcase and export them to the intake manifold. When the emission gets to the intake manifold, the intake manifold sends them back to the engine for another combustion cycle to repeat, making the engine emission cleaner and more effective.

What Happens When a PCV Valve Fails?

Symptoms of a Stuck Closed PCV Valve or System

A bad PCV valve or related component can produce a number of symptoms. For example, if the valve clogs, or gets stuck in the closed position, you'll notice one of these symptoms.

  • Increase in internal engine pressure
  • Failure of one or more oil seals or gaskets
  • Engine oil leaks
  • Low whistling or moaning noise
  • Moisture and sludge buildup inside the engine
  • Engine surges
  • MAF sensor trouble code
  • P0171 or P0174 trouble codes
  • 02 sensor trouble codes

Symptoms of a Stuck Open PCV Valve

If the PCV valve gets stuck open, or a system hose gets disconnected or ruptured—producing a vacuum leak—you'll notice one or more of these symptoms.

  • Engine misfires at idle
  • Lean air-fuel mixture
  • Presence of engine oil in PCV valve or hose
  • Increased oil consumption
  • Hard engine start
  • Rough engine idle
  • Possibly black smoke
  • Oil fouled spark plugs

A PCV valve stuck open can trigger the "check engine" light due to increased airflow. A diagnostic computer may erroneously blame this light on a mass airflow sensor or oxygen sensor instead, making it harder for you to detect the real source of the problem.


PCV Valve Replacement Cost

The average PCV valve replacement cost is between $50 and $250, depending on the car model and labor costs. A PCV Valve mostly costs between $20 and $50. The labor cost is between $30 and $200 at a mechanic workshop.

The replacement cost of faulty PCV valves can differ significantly depending on the engine and the car you have. However, the PCV valve’s price is often meager, and you can expect prices of around $20-50 for a brand new valve.

If you think you have the knowledge to replace the valve yourself, you will not suffer from the labor costs, but remember that it can be difficult to replace it if it’s located under the manifold on some cars.

If you want a mechanic to replace it for you, you can expect a labor cost of $30-200, depending on the location and the car type.

Overall, if you have an older car, the PCV valves are often easy to replace and should only take around 10 minutes, while on newer cars, there could be a replacement time of over 3 hours if it’s located under the intake. Sometimes, you have to remove the intake to access the PCV valve; luckily, this is not that common.

Bad PCV Valve Symptoms

To ensure that your vehicle emits the cleanest and lowest emissions possible, it must have a properly working PCV valve. Sadly, PCV valves might fail after many years of usage.

You must identify bad PCV valve symptoms in your car if you want to replace it. The majority of such indications are pretty easy to spot.

Simply be cautious not to overlook these signs, as they might result in irreparable harm to your engine. The following are the most prevalent indications of a malfunctioning PCV valve.

Poor Fuel Economy

Once your PCV valve becomes jammed closed, your fuel efficiency may suffer. This occurs since your PCV valve allows certain air into your engine while it’s open, which would be taken into consideration by your engine control unit (ECU).

This assists the computer (ECU) in adjusting the air and fuel mixture adequately. However, with your PCV valve jammed closed, insufficient air will reach the engine, resulting in the running rich of your engine.

This reduces fuel efficiency and raises the level of emissions produced by your engine.

Contaminated Filter

If your PCV valve fails, a filter known as a breather element might get polluted with oil and hydrocarbons.

This is caused by rising crankcase pressure that forces water vapor thru your breather element. Water combines with the gas, causing a buildup and perhaps increasing your car’s fuel efficiency.

A physical inspection of this filter for accumulation is one approach to evaluate this component. Another method is to determine your vehicle’s fuel economy. If it begins to drop suddenly, your PCV valve could be failing.

Rough Idle/Increased Idle RPM

Since your PCV valve regulates airflow across your intake manifold and crankcase, a damaged PCV valve might exhibit the same symptoms as the intake air leak.

Resulting in excessive idle RPM and various peculiar idling patterns such as a highly rough idle. If you’re experiencing unusual idling issues, it is usually prudent to inspect your PCV valve first.

Lean/Rich Mixture

Due to the difficulties outlined, a malfunctioning PCV valve might present with similar indications like the intake leak, resulting in an incorrect air/fuel mixture.

Typically, the air/fuel mixture becomes lean, and you’ll experience the very same signs associated with a lean mixture. Due to a rich mixture, you’ll usually notice that your vehicle produces somewhat more white or gray smoke than usual, as well as a strong scent of petrol.

Although a lean combination is more challenging to determine, it frequently results in misfires.

Strange Engine Noises

If either your PCV valve or valve hose fails, your engine may begin to make unusual sounds. You could hear a whirring or whistling noise coming from behind your hood.

This noise is created by air escaping out of your valve or its valve hose’s hole. Keep an ear out for noises or other unexpected engine noises since an irregular noise nearly usually indicates something is incorrect.

Engine Misfires

Since a malfunctioning PCV valve might result in a complex lean/rich mixture, you could notice misfires during idle and acceleration if the PCV valve is damaged.

When the mixture is excessively lean, your cylinders won’t ignite properly, resulting in misfires. The fuel may effectively extinguish the spark whenever the mixture is excessively rich, resulting in a misfire.

Rough Acceleration

Once you have a malfunctioning PCV valve resulting in an incorrect fuel mixture, you will notice that your automobile accelerates poorly at lower and higher RPMs.

While most automobiles will not feel a damaged PCV valve above idle, it’s worth noting since it might occur based on your valve’s configuration.

Engine Oil leaks

As you’re probably aware, the PCV valve allows gas to escape from the engine crankcase. Once your PCV valve fails to function correctly, gas accumulates within the crankcase, increasing its internal pressure.

When the pressure within the crankcase reaches a certain level, it could push engine oil out via the multiple gaskets and seals.

Take note when you notice some oil puddling underneath your vehicle. And if so, examine your engine and its crankcase for any oil leaking out from behind the seals. This might be an indication of a clogged PCV valve.

Black/ White/ Bluish Exhaust Smoke

If your PCV valve becomes jammed shut, the pressure inside your crankcase could naturally rise. Oil might seep out from the seals due to this, but it might also be driven up towards your combustion chambers.

When this happens, the engine oil will begin to burn, altering the color of your exhaust. To be more precise, the exhaust gas would be much smoky than typical and could have a bluish hue.

Blue exhaust fumes are by far the clearest indicator that your engine is consuming oil, and you must never overlook it once you detect it.

Engine Stalling

Whenever your PCV valve fails, its plunger may remain open. An abnormally large volume of air will enter the combustion cylinders when this occurs.

This results in a lean air/fuel mixture since there’s more air inside the cylinders than fuel. As a consequence, your engine could stall or idle poorly.

Check Engine Light

Your dashboard’s check engine light is arguably the most prevalent and apparent indicator of all malfunctioning PCV valve problems. Your engine control unit stores a fault code whenever your engine light comes on.

To read your engine control unit’s fault code, you must utilize an OBD2 scanner. Certain older vehicles equipped with a PCV valve but not equipped with an electronically regulated engine won’t exhibit this sign.

How to Test Your PCV Valve

If you are experiencing any of the problems outlined above, then there is a chance that your PCV valve has failed or is stuck open. The problem, as we have described, is that you may not get precise readings from your diagnostic computer as to the cause of the problem. If none of the issues highlighted by your engine check system is the problem, then you need to check the PCV valve. There is no one PCV valve test; however, there are a few steps you can take to determine whether it is working correctly.

To do this, you need to first identify the PCV valve and the hoses connected to it. Begin your checks by inspecting the rubber parts of the valve. If these are worn, then the part needs to be replaced. Next, identify the mesh filter beneath the valve and replace it. If this does not solve your problem, then disconnect the hoses and scrutinize them. Deal with any issues you find here or replace the hoses if needed before reconnecting and checking if the problem is solved. One final test is to remove the valve itself and give it a shake. If the PCV valve does not rattle, then it needs to be replaced.

3. Overall poor performance

As the PCV valve starts going bad, the performance of your vehicle will get worse. This can be exhibited by a buildup of pressure in the exhaust or the engine could stall out. The bad PCV valve may not close all the way, so oxygen may get into the combustion chamber. When this happens, the fuel and air mixture is diluted causing your vehicle to run poorly and lean out.

If you notice your vehicle is leaking oil, consuming large amounts of oil, you have a contaminated filter, or the car is not working like it should, have the PCV valve looked at and replaced. This will keep your vehicle running smoothly and keep your fuel economy where it should be. YourMechanic makes getting repairs to your positive crankcase ventilation valve easy by coming to your location to diagnose or fix issues. YourMechanic’s experienced technicians are also available for any questions that may arise. You can book a service online 24/7.


PCV system issues might be more challenging to identify if they are not related to the valve. Bring it to your trusted mechanic to examine it over when you suspect a problem elsewhere but are unsure what it is.

If it gets to that point, you might require more professional assistance. If the issue is just your PCV valve only, you would have no problems resolving it on your own. It’s probably of the simplest tasks you can accomplish by automotive measures.

Keeping an eye on the state of your PCV valve ensures that your engine operates at peak efficiency, keeping you secure and sparing you money. Ascertain that your understanding of the signs of a malfunctioning PCV valve is updated to ensure that you can have it repaired asap.

We hope that this article was informative and will assist you in diagnosing the problem with your vehicle.


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Replacing a PCV Valve

The PCV valve can have problems, but more than likely, the PCV valve filter is the culprit. Filters are incredibly important components of your car. You’re likely familiar with the oil filter and air filter. The PCV valve filter is an essential part of the PCV valve, as it captures most of the toxins in the gas stream. Over time and natural wear, the filter can become clogged with road debris and grime.

It is recommended that the PCV valve filter be replaced every 60,000 miles. Regular servicing will include a check of this filter, so your trusted BMW mechanic will alert you if they feel it is necessary to replace this before that mileage mark.

Common Trouble Codes Associated with the PCV Valve

Some common trouble codes appear with a faulty PCV valve. If you experience any of these trouble codes from your engine control unit, it’s probably time to check the PCV valve.

Remember that just because you see these trouble codes, it’s not 100% that the PCV valve is broken. These codes can also be other things, and I always recommend you carry out proper troubleshooting before replacing any parts.

  • P052E – Positive Crankcase Ventilation Regulator Valve Performance
  • P0171 – Fuel System Too Lean (Bank 1)
  • P0300 – Random/Multiple Cylinder Misfire Detected
  • P053A Positive Crankcase Ventilation Heater Control Circuit /Open

The PCV Valve Can Become Stuck

It is possible that the PCV valve can become stuck, failing to do its job to reduce harmful vapors from circulating in the engine. However, there is another sensor that mimics the same problems. This is the MAF sensor. It has similar symptoms as a stuck PCV valve. The MAF sensor is easier to repair. Tell your mechanic if you note any of the following, which could point to an malfunctioning MAF sensor:

  • your engine misfires while idling
  • running lean or rich
  • increased oil consumption rate
  • troubles with ignition
  • rough idling

When to Replace Your PCV Valve

In theory, the PCV valve should last more or less indefinitely, and will only need to be replaced if it actually breaks. However, it’s possible to restore a gunked-up valve to its original condition by cleaning it.

Dirty Vs Clean PCV Valve
Dirty Vs Clean PCV Valve

Cleaning the valve is actually pretty easy;

  • Just get yourself some carburetor cleaner, pour some of it into a container, and let the valve soak in it for a while.
  • The valve can be considered clean once it’s free of gunky deposits and if the valve’s color appears even. 

If this doesn’t work, you’ll have to swap out your old valve for a new one, but luckily this is also pretty easy. All you need to do is remove the old valve from the valve cover and disconnect it from its hose, install the new valve, and reconnect the hose.

Can I Still Drive With a Bad PCV Valve?

Technically you can, as a bad PCV valve doesn’t present any immediate safety issues, but we’d strongly recommend against it nonetheless. While you as the driver won’t be in any immediate danger from a bad PCV valve, your engine certainly will be. Driving for too long with a busted valve can cause all sorts of mechanical problems.

If your valve has indeed stopped working, you should have it fixed as soon as you can, unless you want to run the risk of having to fix significantly more expensive failures in the future. 


You can also check the PCV for the vacuum once you recognize the symptoms of a bad PCV valve. Let the engine warm up for about twenty minutes to check with the vacuum. Access the hood and disconnect the valve from the valve cover. When you block the end of the valve with your finger, it feels like sucking your fingertip. You would notice a speed drop of about 40 to 80 rpm.

When the RPM is more than that, the valve might be stuck open. When you feel no suction effect, check the valve and hose for any obstruction and clean it. You can also clean the valve and hose with lacquer thinner and a thin hose brush, and you are done.