pcv valve symptoms

PCV Valve Symptoms, Function & Replacement cost

In Engine by Josh S1 CommentLast Updated: December 16th, 2018

pcv valve symptomsYou have probably heard about the PCV valve before in a gas/petrol engine.

But you did probably not know how important this little part is to the engine. This little piece is a very common problem and the problem occurs in almost all different petrol engine manufacturers.

Most of the PCV valves are made of plastic hoses with a spring inside. As you can imagine, any plastic would worn out after 10 years mounted in a hot place like the engine bay and because of the importance of the PCV valve, you will get a lot of different symptoms of it when it fails.

In this article, you will learn everything you have to know about the PCV valve. Let’s Begin with the symptoms of a bad PCV valve.

Bad PCV Valve Symptoms

As you now know that the PCV valve is very important for the engine to run properly, you do probably understand that there are a lot of different symptoms associated with the PCV valve. Here are the most common symptoms when it comes to a failed PCV valve.

1. Check Engine Light

A very common problem when it comes to a faulty PCV valve on modern cars is that the check engine light is starting to flash on your dashboard. When the engine light is showing up, there is a trouble code stored in the engine control module. To read the trouble code from the engine control unit you have to use an OBD2 scanner. Some older cars with a PCV valve fitted without any electronically controlled engine will of course not have this symptom.

2. High Idle RPM/Rough Idle

Because the PCV valve is controlling the air flow between the crankcase and the intake manifold, a broken PCV valve can have the same symptoms as an intake air leak which can cause the idle RPM to get too high and other strange idle behaviours like very rough idle. If you have any strange idle problems it’s always a good idea to check the PCV valve first.

3. Lean/Rich Mixture

Because of the thing we discussed before, about a faulty PCV valve can have the same symptoms as an intake leak, the air/fuel mixture can get wrong. In most cases, your air/fuel mixture will get lean and you can feel the same symptoms as from a lean mixture.

4. Misfires

Because you can get a faulty Lean/rich mixture because of a faulty PCV valve, you can feel misfires on both idle or acceleration when your PCV valve is bad. If you have a too lean mixture, the cylinders won’t fire up correctly and this can cause misfires. If you have a too rich mixture, you can turn off the spark with the fuel and therefore cause a misfire.

5. Rough Acceleration

Also here because of the faulty lean/rich mixture you can feel that your car have rough acceleration both on high and low RPM’s. On most of the cars, you won’t feel a broken PCV valve on higher RPM’s than idle, but it’s worth mentioning because it can happen depending on the design of the valve.

6. Increased Oil Consumption & Oil leaks

If the PCV valve or the hoses to it are blocked by moisture, you will get a very high pressure inside the engine crankcase, which will push the pressure up in the cylinders and out from the gaskets. If you suddenly see several large oil leaks and increased oil consumption on your car, check the PCV valve and the hoses to it to make sure they’re not blocked.

7. White/Black/Blue Smoke from the exhaust

If the PCV valve or the hoses are blocked the crankcase will push up oil into the combustion chambers, which will cause oil to burn inside the engine and go out through the exhaust pipe. This will cause a lot of blue smoke from the exhaust pipe. If the PCV valve faulty and causing a rich or lean mixture to the engine, you can get symptoms like white or black smoke coming out from the exhaust pipe depending on what type of mixture problem the engine has. A short conclusion is: If you see any strange smoke from the exhaust pipe, make sure that the PCV valve is in good shape.

What is a PCV Valve?

PCV valve is standing for Positive Crankcase Ventilation and it is one of the oldest and most used emission devices in a lot of vehicles. The function of the PCV valve is to eliminate crankcase emissions from the crankcase and send them to the intake and therefore combust them again in another engine cycle, which makes the engine’s emissions cleaner and more effective.

pcv valveAlmost all PCV valves are made in the same way, two hosing connectors with a spring-loaded one-way valve inside of it. When the engine is at idle, you have a lot vacuum inside of the intake manifold, which helps the emissions to get sucked out from the crankcase efficiently at lower speeds. When you are revving up your engine and driving on higher rpm’s, the PCV valve will open further and suck out even more crankcase ventilation, which is caused by higher RPM and faster crankcase pressure build-up.

  • Idle/Low RPM: High Vacuum, PCV Valve Half closed
  • Higher RPM’s: Lower Vacuum, PCV Valve Open Fully
  • Backfire from crankcase: PCV Valve closing

If you have a turbocharged engine, you do not want to boost pressure to go into the crankcase, which would cause oil leak and blow gaskets. In this case, it’s really important to have a one-way PCV valve. These valves are designed a bit differently and the PCV valve is only working on idle and low RPM’s. Some PCV Valves do also have 3 connectors for vacuum and which are controlling them with electric vacuum solenoids. These can work in a lot of different ways and we will discuss them in another article.

So how do I diagnosing and replacing my PCV valve then? Let’s go to some common questions regarding the PCV valve.

PCV VALVE OPERATION

How often should I replace my PCV Valve?

There is no fixed interval of when you should replace the PCV valve. However, because the PCV valve is often made of plastic and as you may know – plastic age. Especially because the PCV valve is often mounted in hot places inside the engine bay and because there are passing a lot of fuel/oil inside the hose at all the time. This will cause the PCV valve or the hoses to crack up sooner or later.

If you do not know when your PCV valve was replaced the last time and you have any of these symptoms above in your car, replace it. You can also check the hoses around the PCV valves, if these are cracked or in bad shape, there is a big risk that the PCV valve is in the same shape. The PCV valves are often cheap and easy to replace, so if you feel that you have any strange symptoms or do not know when the PCV valve was replaced the last time, replace it!

Where is the PCV Valve located?

pcv valve locationThis question does, of course, depend on what engine you have. If you have an older engine without turbo, check on the top or at the side of the valve cover. The valve is often fitted directly on the valve cover on these cars. However as you may know already, the PCV valve is fitted somewhere between the intake and the valve cover, so if you can’t find it on the valve cover then check if you can see any hoses that are going from the valve cover to the intake. Somewhere on these hoses, the PCV valve should be located.

On the image, you can see a great example of where the PCV valve is located. Sometimes on newer turbo cars the PCV valve is located inside the hose and can be pretty tough to locate. On Audi/Volkswagen/Skoda/Seat 1.8t for example, it’s located under the intake inside the hose and it can be very difficult to locate if you do not know about it.

How to test if the PCV valve is broken?

There are several ways to test if the PCV valve is broken, both of visually inspecting it and without removing it from the vehicle. Here are some small tips on how to check your PCV valve in a fast and efficient way.

pcv valve

Open the oil cap when the engine is running

This method is great because you can diagnose a faulty PCV valve without removing it. Let your engine run on idle and lift off the oil cap. If you feel that the oil cap is sucked to the engine so it’s difficult to remove it, you have too much vacuum inside the crankcase which is most likely caused by a faulty PCV valve. If you remove the oil cap and you feel that the cap is almost exploding away from the engine, you have too high pressure and this is often caused by the PCV valve. However this can also be caused by other problems like worn piston rings, but it’s a lot cheaper to check the PCV valve first.

Spray brake cleaner/motor starter spray around the PCV valve

You can spray a flammable spray around the intake while the engine is running to find any leaks around the PCV valve or the hoses. If the engine is revving up when you are spraying around it, you definitely have a leak somewhere close to where you applied the spray. In this case, remove the valve and the hoses and check if you can locate the leak. Keep in mind that this is a pretty dangerous method which can cause fires. Always do it with care and have a fire extinguisher close to you.

Visually check the PCV valve & the spring

If you feel that you have too much vacuum or too high pressure inside the PCV valve but can’t find any leaks. Remove the PCV valve from your vehicle and check it visually to see if you can find any damages on the valve or the spring.

Check for any moisture in the hoses

If you have too much pressure inside the engine which is resulting in the engine is leaking oil or smoking blue from the exhaust pipe, it’s time to check for any moisture build-up inside the PCV valve or in the hoses. If you find any, clean it up and fit the parts to your car again and try to see if it solves the problem. If the problem still insists it’s probably time to replace the PCV valve.

Check for any broken/collapsed hoses

Sometimes when the hoses get worn, the hoses can collapse which can cause the hoses to get blocked and cause an increased oil consumption and an increased pressure inside the crankcase. The best way to check this is with the engine running, as the problem might not occur when the engine is switched off. Here are some other tips on how to diagnose and test the PCV valve:

How to Test and Replace PCV Valve on your Vehicle

Why are some PCV Valves heated?

Inside the PCV valve and the hoses, there could be a collection of moisture, condense and other nasty fluids. If you have a lot of condensing inside the hoses or the valve, it can freeze if you live in a colder country. A frozen PCV hose can cause a total block of the flow which can cause some serious damages to your engine because the pressure will rise very high inside the crankcase. A high pressure inside the crankcase will result in oil leaks and oil consumption, and in the worst cases problem with the oil pressure and blown engine sealings.

Common trouble codes associated with the PCV valve

There are some common trouble codes appearing when it’s coming to a faulty PCV valve. If you experience any of these trouble codes from your engine control unit, it’s probably time to check the PCV valve. Remember that just because you see these trouble codes, it’s 100% that the PCV valve is broken. These codes can be other things also and I do always recommend you to do a proper troubleshooting before replacing any parts.

  • 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

PCV Valve Replacement Cost

The replacement cost of a faulty PCV valve can differ a lot depending on what engine and a car you have. However, the price of the PCV valve itself is often very cheap and you can expect prices around 10-100$ for a brand new valve. If you think you have the knowledge to replace the valve yourself you will not suffer from the labour costs, but remember that on some cars it can be pretty difficult to replace if it’s located under the manifold.

If you want a mechanic to replace it for you, you can expect a labour cost of 50-300$ depending on the location and the car type. Overall, if you have an older car the PCV valve are often easy to replace and should only take around 10 minutes, while on newer cars, there could be a replacement time of over 3 hours if it’s located under the intake. In some cases, you have to remove the intake to access the PCV valve, luckily, this is not that common.

Conclusion

So in a conclusion, if you experience any strange problems on idle or increased oil consumption, it’s time to check your PCV valve. The PCV valves are often located on the crankcase cover on older vehicles. The price of the valve itself are often very cheap but the replacement can take a while.

If you have any other questions about the PCV valve, comment down below and I will try to answer your questions as fast as possible.

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Comments

  1. I have a 1995 Honda Civic DX car with a 4 cylinder and 1.6 Liter engine. My mechanic told me that the PCV Valve Cover tube is leaking a small amount of oil and to replacement cost with his labor will cost me a total of $200.00.

    Can you tell me if this is a fair price to pay and also should I get the PCV Valve Cover and Hose replaced as soon as possible? What kind of damage will be done if I don’t get the PCV Valve Cover and Hose replaced?

    Thank you,

  2. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
    Ask A Mechanic

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