8 Symptoms Of Bad PCV Valve : How To Test It & Replacement Cost

pcv valve

PCV valves are used in the internal combustion engines of vehicles to remove the gases produced by combustion inside the engine.

But sometimes, when the PCV valve of the engine gets damaged or blocked, many engine-related problems can arise, affecting the functioning of the engine.

Through this post, you will learn about the PCV valve in detail. Like, what is a PCV valve? What are the symptoms, location, and replacement cost of a bad PCV valve?

What is A PCV Valve In Engine?

PCV valve, also known as positive crankcase ventilation valve. It is an important component used in internal combustion engines. Which controls the amount of gas formed between the engine’s crankcase and the air intake manifold.

The PCV valve directs the gases into the intake manifold in the engine’s crankcase, where they can be burned with the engine’s combustion action. This process reduces pollution from the engine as well as improves overall engine efficiency. The PCV valve is a one-way valve and is installed near the valve cover of the engine in most vehicles.

In many turbocharged vehicle engines, the PCV valve also directs gases from the crankcase into the turbocharger line. Due to this, these gases can be burned during the combustion process of the engine.

Related Article : What Is A Seized Engine & Cost To Rebiuld It?

Symptoms of Bad PCV Valve

A bad PCV valve has various symptoms, including rough idle, reduced fuel efficiency, gas coming from the oil gauge, exhaust smoke issues, engine misfiring, increased oil consumption, and engine roughing. Additionally, you may notice excessive oil leakage, sludge accumulation in the engine, or a check engine light illuminated.

1. Gas Coming From The Oil Gauge

Whenever the PCV valve of an internal combustion engine is damaged or blocked, the most common symptom is gas coming out of the oil gauge when the engine reaches running temperature.

Because when the engine is started Then gases build up in the crankcase of the engine. But when the PCV valve fails, these gases are unable to escape and get trapped in the crankcase.

The oil gauge mounts to the crankcase chamber of each engine. When the oil gauge is pulled out, it shows gas coming out when the engine is started.

2. Excessive Engine Oil Consumption

A failed PCV valve in any vehicle with an internal combustion engine can cause excessive oil consumption.

Because when the PCV valve is clogged or stuck in the closed position, it is not able to allow gases to flow from the engine’s crankcase into the air intake manifold.

Due to this, the pressure of gases inside the crankcase of the engine increases, and the excessive pressure of these gases causes leakage of engine oil seals and gaskets, resulting in high oil consumption.

3. Rough Idling

A faulty PCV valve in any internal combustion engine can cause poor or unstable idling of the engine. A bad PCV valve or a valve stuck in the closed position can disrupt proper air-fuel mixing in the engine’s intake manifold, causing irregular combustion and rough idling.

However, there can be many other reasons for poor engine idling. For this reason, it is a good idea to investigate the reasons for the poor idle.

4. Decreased Engine Performance

Often, the PCV valve of any internal combustion engine can degrade overall engine performance. Because the restricted flow of gases from the crankcase to the intake manifold can create an imbalance in the air-fuel mixture essential to the engine’s combustion, the engine may produce low power, hesitation, or sluggish acceleration.

5. Increase Emissions

A bad PCV valve can cause an increase in emissions from the engine. Because a bad PCV valve is not able to effectively direct the flow of gases from the engine’s crankcase to the intake manifold.

This leads to an excessive accumulation of unburned hydrocarbons and other pollutants in the crankcase and increases emissions.

6. Engine Misfire

A faulty PCV valve can cause misfires or rough running in an internal combustion engine. Because of a failed PCV valve, improper crankcase ventilation of the engine can disrupt the combustion process, which can lead to engine misfires. Often, this problem becomes more frequent under engine load or during acceleration.

7. Excessive Smoke From Exhaust

If an internal combustion engine’s PCV valve is stuck in the closed position or has gone bad, it can cause excessive smoke to come from the exhaust. This may be due to the increased pressure of the gases in the enlarged crankcase.

The increased pressure of the gases in the crankcase pushes the engine oil beyond the seals, causing the oil to burn in the exhaust pipe and emit smoke.

8. Oil Leakage Issues

Often, a failed PCV valve in any internal combustion engine can result in higher than normal pressure inside the engine’s crankcase.

And the excessive pressure of the gases can damage the engine seals, and these damaged seals cause oil leakage from the engine.

What Does The PCV Valve Do?

The PCV valve is a one-way valve and opens according to engine vacuum. When the engine is started, gases are produced in the crankcase of the engine during the combustion process and these gases need to escape from the crankcase. Because if excess pressure from gases builds up in the crankcase, it can cause oil leakage from the engine.

When the gases in the crankcase of the engine are pressurized, the PCV valve opens and sends these gases to the air intake manifold and in the intake manifold, these gases are mixed with the air fuel mixture and ignited during the combustion process.

The PCV valve reduces the emission of harmful pollutants from the engine and supports the efficient operation of the engine.

Where Is The PCV Valve Located?

Often, the PCV valve in internal combustion engines is located near the top of the engine valve cover. But in some engines, the PCV valve may also be located on the hose pipe between the crankcase and the intake manifold. 

How To Test a PCV Valve?

Testing the PCV valve in a vehicle’s engine is an easy process. For this,

  • First find the location of the PCV valve, which is usually attached to the valve cover or intake manifold.
  • Next, with the engine running, disconnect the hose connected to the PCV valve and place your thumb over the valve opening.
  • During this time, you should feel a strong vacuum suction.
  • If strong vacuum suction is being achieved, the PCV valve is functioning properly.
  • If not, remove the valve from the engine and shake it.
  • If it rattles, it is in good condition.
  • If there is no rattle, the valve is clogged or bad, so it must be replaced.

PCV Valve Trouble Codes

Often, the check engine light on your vehicle’s dashboard will come on when the PCV valve is failing or bad. Which indicates some problem related to the engine and system of the vehicle.

When this happens, you should have the vehicle’s system scanned with a digital scanner. You may see the following fault codes if you have a bad PCV valve:

  • P0171 – System Too Lean (Bank 1)
  • P0174 – System Too Lean (Bank 2)
  • P0507 – Idle Air Control System RPM Higher Than Expected
  • P052E – Positive Crankcase Ventilation Regulator Valve Stuck Closed
  • P052F – Positive Crankcase Ventilation Regulator Valve Stuck Open
  • P053A – Positive Crankcase Ventilation Heater Control Circuit/Open

Clogged PCV Valve Symptoms

A clogged PCV valve has many symptoms, including increased oil consumption, decreased fuel efficiency, rough idle, and poor engine performance. You may also notice signs of excessive oil leakage, sludge accumulation in the engine, and the presence of a check engine light.

PCV Valve Stuck Open Symptoms

When the PCV valve gets stuck in the open position, several possible symptoms include increased oil consumption, the check engine light illuminating, reduced fuel efficiency, and excessive smoke from the tailpipe due to burning oil. Additionally, you may experience decreased engine performance, rough idle, and possible contamination of the air-fuel mixture.

PCV Valve Replacement Cost

On average, the replacement cost of a new PCV valve can range from $40 to $80, and the estimated cost will include mechanic labor costs.

PCV valve parts cost on average $15 to $25, and the labor cost of replacing a PCV valve by a mechanic can be expected to be $25 to $55.

In fact, PCV valve replacement is not that expensive. Because it is a small component, it is installed above the valve cover in most engines. Which is easy to change.

If you replace the PCV valve yourself, you can save on mechanic labor costs. However, depending on the location, replacing a PCV valve may increase or decrease the mechanic’s labor costs.


Q. What happens when a PCV valve goes bad?

When a bad PCV system malfunctions, it can increase oil consumption as pressure builds up in the crankcase and vapors are not allowed to flow into the combustion chambers. Due to which this additional pressure can force oil past the seals and gaskets.

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