11 Bad PCV Valve Symptoms & Replacement Cost

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bad pcv valve symptoms

Every day, you count on your automobile. It is meant to transport you securely and pleasantly between points A and B. Still, its capacity to do so is highly dependent on how properly it is maintained, making routine service critical.

Every internal combustion engines create gases that enter the crankcase through its piston rings. The crankcase should be vented to prevent issues, including moisture in your oil and too much pressure from occurring.

However, these gases can’t be immediately discharged into the environment since this would increase dangerous pollutants. That’s why, since the 1960s, car manufacturers have equipped automobiles with PCV systems.

Numerous systems use a positive crankcase ventilation valve (PCV valve) to control the passage of crankcase gases. As with every automobile component, the PCV valve will inevitably fail, leading to issues that must be addressed immediately.

Most PCV valves are constructed of plastic hoses containing an internal spring. All plastic will deteriorate after about ten years when installed in a heated location such as your engine bay. Due to its critical nature, you might detect various symptoms once your PCV valve fails.

Thankfully, the PCV valve is inexpensive and straightforward to repair, which means you can DIY it regularly to ensure your engine runs smoothly. Understanding the signs of a faulty PCV valve and diagnosing and fixing it is essential to learn automobile maintenance skills.

In this article, we’ll discuss how a PCV valve operates, the bad PCV valve symptoms, and how to resolve any PCV valve-related difficulties that may arise. Read on to learn more!

Bad PCV Valve Symptoms

  • Poor Fuel Economy
  • Contaminated Filter
  • Rough Idle/High Idle RPM
  • Lean/Rich Mixture
  • Strange Engine Noises
  • Engine Misfires
  • Rough Acceleration
  • Engine Oil leaks
  • Black/ White/ Bluish Exhaust Smoke
  • Engine Stalling
  • Check Engine Light

What Is A PCV Valve?

pcv valve

As previously stated, your PCV valve is utilized to exhaust gas from your crankcase. You might be wondering why this is required in the first place, so let’s explore more.

Once fuel is used in your engine, the waste gases are produced as a byproduct. In contrast, most such gasses escape the engine through your tailpipe. Some could get through your pistons and into your crankcase, which contains the engine oil.

Whenever enough gas enters your crankcase and combines with your engine oil, a thick, foul-smelling, greasy sludge forms. This sludge is very detrimental to your engine since it could damage engine components and block the system’s multiple oil channels.

Your  PCV valve is designed as a one-way valve that permits all gases that penetrate your crankcase to go back into your engine and be burnt.

Since approximately 70% of overall waste gas exiting your engine is unburned fuel, diverting the gases from your crankcase back into your engine. Not only does it assist in maintaining the quality of your engine oil, but it also keeps your engine running more efficiently.

In terms of location, your PCV valve is often situated on top of the valve cover, where it is readily accessible. Look for a tiny tube that runs between your valve cover to your air intake; you should have no difficulty locating it.

It’s critical to keep in mind that although most modern cars come equipped with a PCV valve,  this isn’t the case for every automobile on the street. Before you invest too much effort hunting for this valve, it might be worthwhile to determine if your vehicle is equipped with one.

PCV Valve Function

Your PCV valve is a spring-loaded one-way check valve plunger that’s used to control the passage of blowby gases. This valve’s one end connects to your manifold vacuum hose, whereas the opposite end typically goes into your engine’s intake valley or valve cover.

Once your engine is turned off, the PCV valve’s internal spring causes the plunger to shut. However, the plunger is pulled open by manifold suction if your engine is going. The open PCV valve subsequently draws in new air entering your engine through a breather line. As a consequence of the scavenging action, blowby gases are drawn into your PCV valve.

Upon exiting the valve, these gases are routed by a rubber tube to your engine’s throttle body or intake manifold. These gases are then introduced into the engine and usually burnt during combustion.

However, your PCV valve can’t always allow the very same quantity of blowby gas to penetrate your engine. Rather than that, the PCV valve controls the circulation using its internal plunger, as follows:

  • If the manifold vacuum is strong, blowby output is minimal. In this stage, the vacuum forces the tapered-shaped plunger out of its seat, allowing gases to flow solely via the plunger’s small crevices.
  • As the vacuum diminishes and its blowby grows, the plunger slides farther away from the seat till it reaches the maximum stream. The crankcase gases could enter your engine’s intake system quickly and freely.

However, that is not all. Additionally, your PCV valve protects against backfires if required. When there’s a backfire inside your intake manifold, the internal plunger of the PCV valve is driven into the crankcase, restricting the flame in igniting the gasoline fumes within.

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 Examine Your PCV Valve

Once you notice one or several of the symptoms above of a faulty PCV valve, it’s essential to check the component and determine what may be causing it to fail.

Examine the PCV Valve Grommets

Based on how your valve is linked to your engine, the indications of a faulty PCV valve could be generated by the hoses connected to your valve and various fastening elements.

Typically, a flexible rubber grommet is put into a slot in your valve cover for securing and sealing your PCV valve.

Occasionally, the valve might twist or screw into place and be sealed by an O-ring. Whatever configuration is used, the PCV valve should constantly be sealed entirely to your engine, implying that any leakage is an issue.

By their very nature, O-ring seals and rubber grommets stiffen and fracture or break with time, resulting in oil leakage and enabling pollutants to penetrate your engine. That’s why anytime you replace your PCV valve.

It would be best if you also changed its O-rings or rubber grommets as a precaution. Bear in mind that grommets are available in several styles, relying on your engine configuration, so be careful to choose the correct one.

Examine PCV Valve Hoses

Natural degradation is also a problem with PCV intake and output hoses. They would stiffen with time and may fracture or break.

While the hoses on your PCV system are supposed to remain oil-resistant, inspect to see if they are oil-saturated and bulge, which would impair their capacity to seal correctly.

Any leaking PCV inlet hose or outlet might enable impurities into your engine, resulting in the Check Engine Light illuminating.

Always change PCV hoses using a high-quality brand valve hose. By installing the incorrect PCV hoses, you are very certain to have sludge and oil leaks accumulation and various PCV system issues.

Examine the PCV

If none of these steps resolves the issue, locate and replace your mesh filter, too, though. If it still is not enough, continue with your PCV valve.

Examine the PCV Valve

The last step is to inspect the PCV valve itself. Your PCV valve is typically uninstalled by pulling it out of your valve cover grommet and disconnecting the rubber vacuum line afterward.

A functioning valve will always produce some rattling. Try shaking your PCV valve and listen for the rattle.’ When there is no sound, your PCV valve must be replaced.

Check for Moisture Contamination

While evaluating your PCV valve, look for signs of moisture contamination, such as a hazy or creamy film on your PCV valve or its hose. If there’s moisture within the PCV system, the PVC valve must be replaced.

That stated, moisture in your PCV valve is a sign of additional issues, and just changing the PCV valve won’t resolve the problem; you must also replace the oil. Otherwise, the issue will persist, and the symptoms will eventually reappear.

Usually, when you drive your car on short trips, significantly less than 10 miles, moisture accumulation is more severe, necessitating more regular oil changes. Along with oil changes, attempt to schedule your errands in such a way that each time you flip your key, you’re traveling for a lengthier period.

However, additional engine difficulties might contribute to moisture contamination if the moisture accumulation issue isn’t resolved. Since moisture is a liquid, it passes past your engine oil filter. It is one of the reasons for the increased frequency with which you should replace your oil.

The other cause is that whenever you make many short trips of less than ten miles, your engine doesn’t have the chance to attain working temperature. This is critical since once your engine is suitably warmed up, the heat generated by its oil enables your engine’s extra moisture to boil.

When you drive long enough, often approximately 20 minutes, your PCV system would be able to remove the majority of the moisture out of your oil through steam.

How To Replace The PCV Valve

PCV valves aren’t standard equipment on all vehicles. If your vehicle includes one and your engine has started running or idling rough, or the problem warning light has illuminated. It would be best if you inspected your PCV valve to ensure it’s not blocked with sludge from impurities in the exhaust gases or jammed in a wide-open setting.

A clamp is frequently used to secure a hose connecting to your PCV valve. Occasionally, a small L-shaped housing protects the tip of your PCV valve on the mouth of its hose. Below are the instructions on how to uninstall your PCV valve from your car to evaluate, clean, or change it:

Step 1

Locate your PCV valve and release its hose clamp if applicable, or remove the tiny L-shaped cover from the valve’s end.

Step 2

Disconnect the PCV valve. Certain PCV valves are secured by a rubber grommet and could be easily removed. Some are connected with threads. If you cannot detach your PCV valve manually, use a combination wrench or a tiny crescent wrench to grab its bottom.

Step 3

Conduct a visual inspection of the hose and clamps or grommets. Take the hose off and blow it out. Change your hose if it’s dried, stiff, mushy, spongy, or clogged with sludge or tough residues. Change the clamps and grommets if they are rusted or seem to have degraded.

Step 4

Reinstall the PCV valve by screwing it in. If the replacement valve requires screwing in, do it manually to prevent damaging its threads in your valve cover. Ascertain that your PCV valve is well installed (it must stick a bit when you attempt to remove it again), but avoid over-tightening!

Step 5

Repair the hose connection to your PCV valve. Start your engine and inspect for leaks surrounding your PCV valve.

PCV Valve Replacement Cost

The cost of replacing your PCV valve ranges from $50 up to $250, based on vehicle type and labor expenses. Typically, a PCV Valve costs around $20 up to $50. At an auto repair, labor costs range from around $30 up to $200.

The cost of replacing malfunctioning PCV valves varies significantly according to your vehicle and engine. However, your PCV valve is frequently inexpensive, costing roughly $20 up to $50 for a fresh new PCV valve.

Suppose you believe you possess the skills necessary to replace your PCV valve yourself. In that case, you’ll save labor expenses, but keep in mind that it may be difficult to change if it is positioned under your intake manifold on certain vehicles.

Suppose you need a professional to restore it for you. The labor cost will range from $30 up to $200, depending on your location and the kind of vehicle.

In general, if you own an older vehicle, its PCV valves are primarily simple to replace and will take no more than ten minutes. However, the replacement duration may exceed three hours on modern vehicles if its valve is positioned beneath the intake manifold.

Occasionally, you will need to dismantle your intake manifold to reach the PCV valve; fortunately, this isn’t a typical occurrence.


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.


How long can I continue driving with a faulty PCV valve?

Although your PCV valve is inexpensive, it must be replaced at specified intervals – around 30,000 to 50,000 miles. It’s never advisable to operate a vehicle with a malfunctioning PCV valve for an extended period. Driving for up to ten hours with a faulty PCV valve is very unsafe.

Can I clean my PCV valve with WD-40?

Absolutely, WD-40 can be used to clean your PCV valve. Simply separate your PCV valve from its rubber grommet on your valve cover and intake manifold, apply WD-40 on it, let it penetrate and disintegrate the dirt and dust within, then rinse it with WD-40. But, We don’t advise cleaning a blocked PCV valve — a high-quality valve can be purchased for less than $10.

Is it possible for a faulty PCV valve to burn oil?

Due to your engine’s high pressure, a malfunctioning PCV valve may cause significant engine gaskets to leak oil, leading to increased oil consumption or oil patches on your car. Ascertain that you examine or call a qualified technician to check and replace your defective PCV valve.

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