Bad PCV Valve Symptoms, Causes, And Replacement Cost

The crankcase is one of the most important parts of the engine. All the extra gasses from the crankcase of the car’s IC engine are removed through the crankcase ventilation system. The main components of the crankcase ventilation system are a one-way valve, a tube, and a vacuum source. A Positive Crankcase Ventilation valve (PCV valve) helps to reduce the emission rate of harmful gases. This article mainly explains the symptoms, causes, and replacement cost of a bad PCV valve.

What is PCV Valve?

PCV valve stands for Positive Crankcase Ventilation valve. PCV valve is the conventional emission device that has been used in vehicles to reduce exhaust emissions.

The main function of the PCV valve is to remove the crankcase emission gases and transfer them to the intake. With the PCV valves, these emissions are combusted twice in a few engine cycles, making the emission of the engine even more clear and more efficient.

PCV Valve

With a unique design and functionalities, these valves work at low speeds or idle. A few types of PVC valves contain three connectors for vacuum. 

How Does a PCV Valve Work?

As the fuel is ignited in the vehicle combustion chamber, many unwanted gases are produced and exhausted through the exhaust system of the vehicle. Some of these exhaust gases make their way to the piston and crankcase, where they mix with the motor oil and generate oil sludge. This sludge can clog the engine passages or may damage some components of your car through corrosion.

At high speeds, the gases in the pistons or crankcase can create a noticeable pressure. This generated pressure may damage the seals and gasket and result in oil leaks in your car. You must install a PCV valve in your vehicle to avoid all these daunting situations.

PCV Valve Working

The PCV valve is the one-way valve that only helps in venting out the waste gases and does not allow them to enter through it. It works as a check valve.

With the entrance of the emissions to the engine block, the spring-loaded plunger of the PCV valve directs the gas flow out of the crankcase towards the intake manifold.

In the two-stroke engine with a special crankcase compression design, the crankcase gases are sent out directly to the combustion chamber. Therefore, 2-stroke engines don’t have a crankcase ventilation system. 

Symptoms of a bad PCV Valve

A fully functional PCV valve is necessary to get the cleanest emissions from your car. With the passage of, your vehicle valves can get bad. As the PCV valve or Positive Crankcase Ventilation valve goes bad, it produces one of the below-given symptoms:  

  • Check engine light
  • Oil leakage
  • Lean or rich air-fuel mixture
  • Engine stalling
  • Misfires
  • Poor acceleration
  • Bad fuel economy
  • White or black smoke from the exhaust
  • Failed emission test
  • Contaminated filter

1) Check Engine Light

One of the most common symptoms of a bad PCV valve is the glowing check engine light on your car’s dashboard. Whenever the engine light illuminates, then a trouble code is stored in your car’s PCM (powertrain control module). Use the OBD-II scanner to read the trouble code and find out the main cause. 

Check engine light

Few types of conventional cars do not have the PCM. Therefore, they do not show that symptom (check engine light).

Read More: How To Reset Check Engine Light?

2) Oil Leakage

An operational PCV valve usually works at lower pressure, but in case of any damage or fault, it may be closed or stuck permanently. This stuck valve can be due to clogging, damage, or due to usage for several years.

Oil Leakage due to a faulty PCV valve

The pressure in the crankcase can increase up to a high amount while driving. In such conditions, if the Positive Crankcase Ventilation valve keeps closed, then the higher internal pressure may lead to oil leaks. 

This oil leak can be from the head gasket and the seal. The non-functional PCV valves can also be the reason for the presence of oil in the air filter assembly. With time this oil may make its way out via the exhaust. So, if you notice oil coming from the exhaust of your car, it may be the symptom of a bad Positive Crankcase Ventilation valve.

Read More: Low Engine Oil Symptoms and Causes

3) Lean or Rich Mixture

Sometimes the symptoms of the intake leak and bad PCV are the same. When the air-fuel mixture becomes lean, it may refer to the same symptoms as a lean mixture.

Sometimes, your vehicle can generate some grey or white smoke (a little different from the normal smoke) and some smell of petrol, which is a clear sign of a bad PCV valve. The lean air-fuel mixture may also cause a misfire.

 4) Engine Stalling

The main function of the PCV valve is to control the airflow between the intake manifold and crankcase.

Engine Stalling

In the case of a bad Positive Crankcase Ventilation valve, its plunger stays open, and the valve does not close properly. Due to this open state, some air flows into the combustor of the car. This leads to the lean mixture of fuel and air in the engine cylinder. As a result, your car goes through rough idling and engine stalling.

5) Misfires

The bad PCV valves may also cause misfires on the idle state or acceleration. That is because a faulty valve delivers a lean or rich air-fuel mixture.

In the case of an excessively lean mixture, the cylinders will not be able to properly combust the mixture which may lead to misfiring.

Engine Misfiring

6) Poor Acceleration

A wrong fuel mixture caused by a faulty PCV valve may lead to rough acceleration on low or high RPM.

Poor Acceleration, symptoms of a bad PCV valve

Some cars may not show proper symptoms of bad PVC valves in higher RPMs but in lower RPMs or idle states. The following exception depends on the design of the PCV valve of your car.

7) Bad Fuel Economy

In case of a stuck PCV valve (PCV valve that is unable to close properly), a rich mixture of fuel and air will be produced in the combustion chamber of the cars. This depicts the presence of more fuel than in the air in cylinders. Since it increases fuel consumption, a bad PCV valve will lower your fuel economy, and you will have to pay more for fuel frequently.

Not only do you have to spend more on fuel, but also, due to toxic emission gases, your car will also fail to pass the upcoming emission test.

8) Smoke from the Exhaust

In case of a clogged PCV valve or hose, the oil will be pushed up to the combustion chambers by the crankcase. This will cause the burning of the oil inside the combustion chamber. After burning the oil, gases will vent out through the exhaust pipe. As a result, blue smoke will come out through the exhaust pipe.

Black Smoke from the Exhaust

In case of a faulty PVC valve and lean mixture, you will observe white or black smoke from the exhaust pipe. These colored smokes are a visible sign of a bad PCV valve in your car.

9) Failed Emission Test

When your PCV valve goes bad, your vehicle will be unable to pass the emission test. 

Failed Emission Test

10) Contaminated Filter

When the PCV valve begins to fail, a filter known as the breather element can become contaminated with hydrocarbons and oil. This occurs as a result of increased pressure in the crankcase, forcing water vapor through the breather element. The water then mixes with the gas, leading to a buildup that can raise your vehicle’s fuel consumption.

To examine this component, you can either visually inspect the filter for signs of buildup or monitor your vehicle’s gas mileage. If you notice an unexplained decrease in fuel efficiency, it could be an indication that the PCV valve is deteriorating.

Read More: Symptoms and Causes of Bad MAP Sensor

What are some common trouble codes associated with the PCV Valve?

Here is the list of some trouble codes that may appear in case of a faulty PCV valve on your OBD2 scanner. If you notice any of these codes in your scanner, it is time to fix your PCV valve accordingly.

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

PCV Valve Location

You can find the PCV valve near the intake manifold in your car. Sometimes, you can find it on the top of the engine on the valve cover, and you can also find it between the valve cover and the air intake filter.

PCV Valve Location

Follow the hose in the car’s engine, and you will find the PCV valve. Sometimes, An Integrated PCV valve is also present in some cars with the valve cover.

PCV Valve Replacement Cost

The cost of PCV valve replacement depends on the car model and the labor cost. According to estimation, it can be from $40 to $260. The PCV valve itself costs between $20 to $60. Commonly, the services or labor costs will be from $20 to $200.

Similarly, the replacement cost of the PCV valve can vary according to the car model and engine type.

FAQ Section

Can I clean the PCV valve by myself?

Yes, if your PCV valve is clogged, you can clean it by yourself, but most of the time, the spring inside the valve gets old and worn out. In the case of a faulty spring, cleaning will not fix the problem. Hence, PCV valves are cheap, so it’s better to replace them to prevent future issues and problems.

Is the PCV valve necessary?

Yes, the PCV valve is important in maintaining the pressure in the crankcase or a car. Without a valve, there can be a lot of pressure in the crankcase during the idle state and a lot of overpressures during turbo boost. This valve also helps in improving the fuel intake of your car by successfully taking the unburnt fuel back to the combustion chamber.

How often should a PCV valve be replaced?

There is no specific lifetime period for the PCV valve. It simply depends on how long it works. With regular maintenance, it can last for a long, and negligence can make its life shorter. But it is recommended to change the PCV valve with every major scheduled service (30, 60, 90K, etc.).

What are the causes of a faulty PCV valve?

  • Wear and tear
  • Contaminants on the valve
  • Accidents
  • Age of the valve
  • Exposure to heat and oil
  • Incorrect installation

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