Top 8 Bad PCV Valve Symptoms (Replacement Cost)

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In modern gasoline and diesel engine vehicles, a Positive Crankcase Ventilation (PCV) system is installed to improve fuel economy and reduce the harmfulness of the emissions coming from the tailpipe. This PCV system’s performance is controlled by a flexible “valve” installed in the assembly.

If the PCV valve fails, it’s quite an easy repair that won’t take up much time – depending on how your car is built. But how do you know that the PCV valve isn’t working anymore?

This article lists the most common bad PCV valve symptoms, which include poor fuel economy, oil leaks, engine misfiring, rough idling, and other signs.

What Does The PCV Valve Do?

As part of the Positive Crankcase Ventilation (PCV) system, the PCV valve is there to help remove gas from the engine’s crankcase. The valve channels the harmful gases back into the combustion chambers through the intake manifold.

Gases in the crankcase are usually harsh (gaseous) vapors that escape from the combustion chambers – through gaps in between the cylinder walls and pistons.

If these unburned gases are allowed to stay in the crankcase for a longer time, the engine’s performance would be badly affected, as the gases can contaminate the motor oil flowing into the engine – tailpipe emissions would be harsher too.

So, the PCV valve helps to send these gases back to where they should be. But then, the PCV valve is liable to fail in the long run; a PCV valve is said to have failed when it is stuck open or close.

Once the PCV fails, it implies that the bad gases that escape the combustion chambers won’t be properly utilized, which could lead to a lot of unusual problems.

Bad PCV Valve Symptoms

There are two ways PCV valves fail; they get stuck open or closed. If stuck open, the symptoms are pretty different from what you may experience if the valve is stuck closed.

Hereunder, we’d explain the various bad PCV valve symptoms.

1. Whistling or Hissing Sound (Closed PCV Valve Symptom)

You’d mainly hear this unusual sound when the PCV valve is shut close. The hissing or whistling sound becomes louder as you drive and seem to be coming from the engine bay. This sound goes out because the PCV valve is stuck close and wouldn’t let gas pass through.

So, as the forcefully withheld gasses struggle to escape, they make a hissing noise. This is a very common sign that indicates you’ve got a stuck closed PCV valve to deal with – have the valve checked as soon as possible.

2. Check Engine Light

Well, the check engine getting illuminated can imply many things, including a bad PCV valve. This symptom can indicate a stuck open PCV valve or a stuck closed PCV valve. So to say, when the check engine light illuminates, one of the things to check when you pop-open the bonnet is the PCV valve.

Notwithstanding, since the check engine light illumination can mean a lot of things, check other parts of the engine after checking the PCV valve.

It’d be best to run troubleshooting using an OBDII scanner or any other auto-scan tool you prefer to use. The troubleshooting would provide you with some handy codes to know exactly what’s wrong with the engine.

3. Rough Idling or Misfiring Engine (Stuck Open PCV Valve)

Rough idles, and engine misfires are pretty common scenarios that occur once there’s a problem with your car’s engine. However, in this scenario, they can indicate a bad PCV valve, particularly a stuck open one.

A stuck open PCV valve can cause misfiring because it opens up for excessive air to get into the intake manifold, which inappropriates the air-fuel mixture in the combustion chambers, hence leading to engine misfiring or rough idling.

For the engine to run smoothly, a specific amount of air and fuel has to mix together in the combustion chambers; if fuel is much more than air, it’s a problem, and if air has a higher ratio, it’s a problem too. So, when next your car engine misfires, check the PCV valve too.

4. Poor Fuel Economy (Stuck Closed PCV Valve)

Everything installed in modern vehicles contributes – in one way or the other – to the car driving with better fuel economy. The PCV valve plays a huge role in fuel economy because it directly affects the combustion process.

When the valve is stuck close, sufficient air won’t be sent into the combustion chamber, which means more fuel would be burnt, and that would lead to high fuel consumption (poor fuel economy). That said, if your car suddenly starts consuming more fuel than usual, you should check the PCV valve.

5. Oil Leaks (Stuck Close PCV Valve)

One of the things the PCV valve does is relieve pressure inside the engine cylinders. Hence, if the valve gets shut off, it builds more pressure inside the cylinders and engine crankcase, as there’s no other way for the compressed gases to escape.

The excessive pressure inside the crankcase may force motor oils in the region to flow into other regions and leak out. Most drivers have alleged they had oil leaks or high oil consumption when their vehicle’s PCV valve was bad.

If you start seeing engine dark oil or fluid leak from beneath the car and the oil filter or head gasket looks good, chances are that the leaks are caused by a clogged PCV valve hose.

6. Dark Smoke From The Exhaust (Stuck Open PCV Valve)

When the PCV valve is stuck open, one of the signs is black smoke coming out from the exhaust’s tailpipe.

The open PCV valve allows oil to get into the combustion chamber, and when oil is present in the combustion chamber, it makes the burned gaseous fumes darker. Typically, the darker smoke has a staunch scent.

7. Oil Fouled Spark Plugs (Stuck Open PCV Valve)

Also, if the PCV valve is stuck open, it could cause oil to penetrate into the combustion chamber and, from there, flow into other inappropriate areas.

So, most times, when you see that the spark plugs are oil-fouled, chances are that you’ve got a stuck open PCV valve.

8. Contaminated Crankcase Vent Filter

The crankcase filter is also called a breather element; it could be covered or clogged with hydrocarbons and oil when the PCV valve is bad. The clog may be a result of the excessive pressure inside the crankcase.

Failed PCV Valve Replacement Cost

Bad PCV Valve Symptoms

The average cost of replacing a bad PCV valve is between $50 and $250, depending on quite various factors. The valve costs around $20 – $70, while labor costs range from $50 to as much as $150.

You may spend more than these estimated costs if some other components would need to be replaced with the failed PCV valve. You can buy PCV valve from PartsGeek or RockAuto stores.

What is a Bad PCV Valve Error Code?

If you troubleshoot your car and get the following error codes, that’s a sign that you’ve got a bad PCV valve.

  • 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

Is The PCV Valve Necessary?

From all indications, the PCV valve is very important and contributes to the effective running of the engine. If the PCV valve is removed, your engine won’t run appropriately as designed; similarly, if the valve is bad, the engine will run anomaly.


This article explains the common bad PCV valve symptoms you may experience when faced with the situation. It is important to fix a bad PCV valve as early as possible before it contributes to bigger problems that would cost more to fix.

The PCV valve is located in the engine bay – usually close to the breather hole on the intake manifold.

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