Car Repair and Maintenance

15 Symptoms of a Bad PCV Valve [Diagnosis, Fix & Replacement Cost]

Positive crankcase ventilation valves, or PCV valves, are crucial components of your car’s engine. This valve keeps the engine operating smoothly by removing gases and vapours. Your car may experience several issues if your PCV valve isn’t functioning correctly. We will be highlighting some symptoms of a bad PCV valve.

Poor engine performance or an oil leak are typical signs of a failed PCV valve. The engine will run lean if the PCV valve is malfunctioning, which will turn on the check engine light.

The presence of an oil leak, higher fuel consumption, and a rough idle are further signs of a faulty or deteriorating PCV valve. If you decide to repair the valve yourself, you should prepare to spend between $10 and $20. You might anticipate paying between $40 and $60 if you hire a mechanic.

In this article, you will learn several symptoms of a bad PCV valve, how to fix it, and the cost you should budget.

symptoms of a bad pcv valve

What is a PCV Valve?

Gases from the engine’s crankcase may be evacuated out via a one-way valve called a positive crankcase ventilation (PCV) valve. The PCV valve is often found at the top of the engine’s side.

It’s crucial to have a mechanism for these greasy fumes to escape since they may accumulate in the crankcase. The intake manifold vacuum of the engine opens and closes the PCV valve. Fresh air is drawn into the crankcase by the vacuum when the engine is operating. The greasy smells are diluted and eliminated by the fresh air.

The vacuum is let go and the spring-loaded PCV valve shuts, sealing the crankcase when the engine is not operating. It is a reasonably simple procedure that can be completed at home to check and replace a PCV valve. Every few months or so, it’s a good idea to ensure the valve is still functioning correctly. The PCV valve can get blocked or malfunction, leading to oil leaks, higher engine wear, and other issues.

Symptoms of a Bad PCV Valve

Look out for the following:

Audible engine noise

This is one of the significant symptoms of a bad PCV valve. While driving, unusual noises are a certain clue that something isn’t operating correctly. A hissing, whistling, or whining sounds coming from the engine, and sometimes a deep moaning murmur, is one of the most typical signs of a faulty PCV valve. The PVC hose’s leak is most likely to blame for the hissing sound.

By temporarily shutting off the vacuum source going to the PCV valve, it is simplest to determine if a faulty PCV valve is a problem. You should take your car to a mechanic immediately if the noise changes or disappears since ignoring it may lead to misfires, rough running, vacuum leaks, and various undesirable performance issues.

Extreme oil consumption

Excessive oil consumption is a symptom of issues with many engine parts and also one of the symptoms of a bad PCV valve, much like many other warning indications. Burning oil can do significant damage to your car’s engine—

You may see a significant increase in oil consumption while operating a vehicle with a blocked or broken PCV valve or hoses, which is not uncommon.

The crankcase won’t have someplace to transfer the extra pressure if the PCV hoses are blocked. As a substitute, it will return the pressure to the chambers, which will cause an oil leak from the other side. Consequently, whenever you check the engine’s oil, you will see that it is decreasing.

When it comes to the engine’s safety, oil decrease is terrible. In extreme circumstances, high oil consumption might destroy an engine.

Check engine light

A malfunctioning PCV valve is one of the potential causes of the Check Engine Light appearing on your dashboard since it interacts directly with your engine. Keep in mind that if you drive an older model car, the PCV system may not have been installed if your engine was electronically controlled; as a result, a faulty PCV valve won’t turn on your check engine light.

A fault code is kept in the engine control unit for when the engine light comes on (ECU). You’ll need an OBD-II scanner or code reader to read the engine control unit’s fault code to determine the precise issue with your PCV system.

The following are some specific issue codes that are often linked to a defective PCV valve:

  • P052E – Performance of the Positive Crankcase Ventilation Regulator Valve
  • P053A – Positive crankcase ventilation heater control circuit
  • P0171 – Fuel System Too Lean
  • P0300 – Detected Random/Multiple Cylinder Misfire

But remember that just because you get the aforementioned codes doesn’t mean a defective PCV valve is to blame for your problems. Other issues can also cause these codes to appear. Because of this, after reading the code, hold off on replacing the PCV valve to pay attention to other odd symptoms and properly investigate the issue.

Misfiring while idle

Misfiring is considered one of the symptoms of a bad PCV valve is the engine misfiring. A misfire will sound like the engine is vibrating, which is a specific indication that the engine is not running at its best.

Typically, when a scenario like this arises, the car is idling. Vacuum leaks, particularly one-cylinder-confined ones that let more air into the afflicted cylinder and disrupt the ideal air and fuel combination, are the cause of engine misfiring.

Engine misfiring may also occur if the vacuum is lost as a result of a blockage in the PCV hose caused by sludge, gasoline, and oil varnish deposits that have accumulated over time, or if the hose is pinched.

Oil spills

Oil spills are considered one of the significant symptoms of a bad PCV valve. The pressure within the engine crankcase will increase if the PCV valve or the hoses are blocked, and because there is no other route for the pressure to be released, the oil in the cylinders will be forced out via the seals and gaskets.

Inspect the PCV valve and the hoses leading to the valve to ensure they aren’t clogged if you suddenly discover many large oil puddles flowing into your garage floor (upon examination, oil is leaking through the seals).

Rough idle

A malfunctioning or damaged PCV valve might present itself in the same manner as an intake air leak because it regulates the passage of blow-by gases from the crankcase to the intake manifold. A defective PCV valve may result in excessively high idle RPMs and odd idle characteristics, such as very rough idling.

Engine running lean/rich and poor fuel economy.

Poor fuel efficiency is one of the indications of a faulty PCV valve. A broken PCV valve will throw off the exact ratio of the air and fuel mixture, which is necessary for ideal combustion.

This is because the vacuum on the cylinder head’s intake side will be unable to accurately estimate how much fuel should be injected into the cylinder for combustion. Another factor is that a defective PCV valve, which may be jammed open or not completely shut, can let oxygen into the combustion chamber.

The gasoline may thus be either light or rich. Poor fuel efficiency results from the delivery of insufficient fuel for optimum combustion.

Fumes from the exhaust

The increased crankcase pressure will force engine oil into the combustion chambers, where it will be burnt and escape the exhaust pipe if the PCV valve or the hoses connecting to it are clogged. Your tailpipe will emit a lot of blue smoke if you burn oil.

Otherwise, depending on the engine’s sort of mixture issue, you might see thick, white or black smoke pouring from the exhaust pipe if the PCV valve is malfunctioning and generating a rich or lean mixture.

Filter contamination

Your car’s crankcase may not be able to manage the increased pressure buildup when the PCV valve ages. Due to the oil-gas combination that results from the crankcase sending water vapour to the filters, the filters get contaminated.


These dangerous combustion byproducts will mix with the engine’s oil when they seep into the area between the piston and cylinder wall. There is a sludge residue left behind when oil and exhaust gases combine, which is one of the typical symptoms of a bad PCV valve.

This gunk will keep accumulating until it eventually harms your engine. The sludge won’t be visible unless you check your engine oil and see it yourself. Due to noisy tappets/lifters brought on by engine sludge, you could even hear ticking from your engine.

Rough acceleration

When a faulty PCV valve throws off the air and fuel mixture provided to the engine, you may experience jerky acceleration at both high and low RPMs. On most cars, this situation will be less noticeable at higher RPMs than it is at idle, but depending on the PCV valve’s design, it may still occur.

What Is the Replacement cost of a Bad PCV valve?

Depending on the car type and labour expenses, the typical cost to replace a PCV valve ranges from $50 to $250. Typically, a PCV valve costs $20 to $50. A mechanic’s business charges between $30 and $200 for labour.

Depending on the engine and the vehicle you own, the cost to repair malfunctioning PCV valves might vary considerably. However, the PCV valve is often inexpensive, and you may anticipate paying $20 to $50 for a brand-new valve. You won’t pay labour charges if you decide to replace the valve yourself, but remember that it could be challenging if the valve is on certain cars positioned beneath the manifold.

Depending on where you are and the kind of car you drive, the labour cost to have a technician repair it for you might range from $30 to $200. In general, if you have an older vehicle, the PCV valves are often simple to repair and should only take around 10 minutes; however, on modern cars, if it’s beneath the intake, the replacement time might be over 3 hours. Fortunately, removing the intake is not often necessary to reach the PCV valve.

How to test a PCV valve

If you see any of the aforementioned symptoms of a bad PCV valve, it’s time to examine the part and determine what could be the source of the issue.

1. Look at the PCV valve grommets

Depending on how the PCV valve is connected to the engine, the hoses to the PCV valve and other mounting components may be the cause of bad PCV valve symptoms.

The PCV valve is typically sealed to the valve cover and fixed in place using a flexible rubber grommet that is put into a hole in the valve cover. The valve may sometimes twist in or screw in and seal with an O-ring. Any leak is an issue since, regardless of design, the PCV valve must always be sealed tightly to the engine.

Rubber grommets and O-ring seals break or split over time because of the nature of their material, creating an oil leak and letting pollutants into the engine. For this reason, you must always replace the rubber grommet or O-rings whenever you change the PCV valve as a precaution. Make sure you obtain the proper grommet since they have different designs based on the engine type.

2. Examine the PCV valve hoses

PCV intake and outlet hoses are also susceptible to damage due to nature. They will get harder with time and may split or fracture. Although the hoses for PCV systems are designed to withstand oil, you should still check to see if they have been drenched in oil and have swollen, which would make it harder for them to close tightly. The Check Engine Light may be brought on by a leaky PCV inlet or outlet pipe that allows impurities to enter the engine.

Always use the original equipment, molded PCV hose that came with your car when you replace it. The incorrect PCV hose types will undoubtedly result in oil leaks, sludge buildups, and other PCV system issues.

3. Check for moisture contamination

Check the PCV valve or hose for moisture contamination in the form of a hazy or milky film when you are checking the PCV valve itself.

You must change the valve if the system contains moisture. Having said that, moisture in the PCV valve is a sign of additional issues, so changing the valve by itself won’t solve the issue; you also need to replace the oil. If not, the issue will continue to exist and the symptoms will eventually reappear.

Generally speaking, moisture accumulation is more significant if you primarily drive small distances, especially under ten miles, which means you will require more regular oil changes.

Try to group your errands so that every time you turn the key, you’re driving for longer cycles along with the oil changes. But even then, if the moisture buildup issue is not resolved, other engine issues could be the source of the moisture contamination.

4. Inspect PCV

If none of these solutions work, locate the mesh filter and replace it as well. Continue with the PCV valve if it still doesn’t do the trick.

5. Examine the PCV valve directly

The valve itself should be checked in the last step. The rubber vacuum hose may typically be removed once the PCV valve has been pulled out of the valve cover grommet.

A functioning valve will constantly rattle. Try to hear the rattling by shaking the PCV valve. If there is no noise, the PCV valve has to be replaced.


Can you clean the PCV valve?

You can undoubtedly clean your PCV valve if it is blocked. But typically, the PCV valve’s internal spring mechanism ages and degrades. PCV valves are often relatively affordable, so even if you can clean them, we advise replacing them to prevent issues soon.

Is a PCV valve necessary?

Yes, driving without a PCV valve may lead to excessive crankcase pressure during turbo boost and excessive crankcase pressure at idle. By recycling unburned gasoline vapours back into the combustion chamber, the PCV valve also contributes to increased fuel economy.

How often must the PCV valve be replaced?

The PCV valve replacement cycle has no set schedule. The PCV valve frequently lasts for more than 100,000 miles. However, if your car is more than a few years old, you might want to replace the PCV valve because it is relatively inexpensive and frequently quite simple.

Is a PCV valve open at idle?

To prevent creating an excessive amount of vacuum inside the crankcase, the PCV valve should be closed or partially closed while the engine is idling. The PCV valve opens completely to release the crankcase gases when you slightly depress the throttle.


The check engine light on your dashboard and a rough idle are typical symptoms of a bad PCV valve. Additionally, you could notice that your engine uses a lot of oil and that blue smoke is pouring from the exhaust.

You should take your car to a mechanic to check the PCV valve if you experience any of these symptoms. Don’t wait too long to replace it if it needs fixing because it’s a small part crucial to maintaining your engine’s health. Doing this will maintain your car in good shape for many years.


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Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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