How to Clean, Test, and Replace a PCV Valve

Most car manufacturers do not provide definite instructions on when to replace your Positive Crankcase Ventilation (PCV) valve. Sometimes, you may not even need to replace it. Cleaning may work just fine. This guide will teach you how to clean, test, and replace a PCV valve.

Depending on the type of vehicle you drive, the valve could be located on top of the engine on the valve cover, or on a hose between the air intake filter and the valve cover. How does a PCV valve work? It uses your engine’s vacuum to suck blow-by gases out of the crankcase. 

Blow-by gases are combustion gases that leak from the pistons, liner system, and rings. They comprise a mixture of air, hydrocarbons, acid, sulfur, oil mist, and particulates. The PCV valve pushes them back into the combustion chamber for further burning to prevent external pollution and carbon buildup

Signs of a Bad PCV Valve / PCV valve symptoms

Most people do not realize how important the PCV valve is until it goes bad. If blow-by gases are left unchecked, they can cause havoc to your engine. The substances found within the gas mixture can dilute and contaminate your engine oil, cause high fuel consumption, corrode metallic parts, cause sludge buildup that in turn accelerates wear, or block small hoses and passages. 

If the PCV valve fails and is left clogged or in the closed position, here are some of the symptoms you may notice: 

  1. Engine oil leaks
  2. Low moaning or whistling sound
  3. Engine surges and jerks 
  4. Sludge and moisture buildup inside the engine
  5. Failed oil gaskets or seals
  6. Increased internal engine pressure
  7. P0171, P0174, O2 Sensor, and MAF sensor trouble codes
  8. Black smoke

If the PCV valve fails and is stuck open, or a hose within the system gets ruptured or disconnected, you’ll have a vacuum leak accompanied by any of these symptoms: 

  1. Increased oil consumption
  2. Rough engine at idle
  3. Presence of oil in PCV hose or valve
  4. Engine misfires at idle
  5. Presence of oil on spark plugs
  6. Hard engine start
  7. Lean air-fuel mixture
  8. Check Engine light 

The same applies if you use your car while the PCV valve is disconnected.

How to test, clean and replace your PCV Valve 

Some of the symptoms highlighted above can be prevented by inspecting and cleaning the PCV valve during maintenance. However, most car owners don’t remember to check the valve or include it as part of their servicing. Here’s a step-by-step process on how to test a PCV valve. 

Step 1: Locate the PCV valve 

The PCV system was introduced in 1961. In some models, it includes a valve that is mounted on one side of the engine and is connected to a breather opening at the intake manifold. In others, it is attached to a rubber grommet on the valve cover. If you’re wondering where is my PCV valve located, start with those two areas.

Some newer vehicles don’t have a valve. They use a vacuum hose that connects from the valve cover to the air inlet duct. Others use a simple restrictor. You can consult your service manual for your particular model or check a reputable online website to confirm this. 

Step 2: Inspect the PCV system 

The next step would be to inspect every component of the PCV system. This includes checking for hard and swollen hoses, grommets, and O-rings. These tend to turn brittle due to high temperatures and can sometimes leak. If that is the case, you’ll need to replace them. Remember to clean any slime or gunk that you meet during the inspection using PCV solvent. 

Read more: How to Clean Plastic Intake Manifold

Step 3: Test the PCV valve

How to Test a PCV Valve

There are different ways that you can test the PCV valve. You’ll need to start the engine and let it idle for about 20 minutes to get it to its operating temperature. Afterward, go ahead and remove the valve from the valve cover with its hose still attached. You may need a PCV valve removal tool.

Place your finger over the open end of the valve and block it. You should feel a strong suction if the PCV valve is working well. But if you don’t, the valve and hoses could be bad or obstructed by gunk. 

The second method of testing the PCV valves will require you to remove it from its hose and shake it. If the valve is working fine and unobstructed, you will hear a solid rattle that is distinct. If the rattle is faint or non-existent, that is a bad PCV valve sound indicating the valve is bad. 

Read more: How to Fix Rattling Noise When Accelerating

Step 4: How to clean PCV valve

How to Test a PCV Valve

Most vehicles use an inexpensive and simple PCV valve that can be easily replaced by the car owner. However, before replacing yours, it’s advisable to first clean it using PCV solvent or by immersing it in carburetor cleaner

Step 5: Replace the PCV valve

If it cleaning the valve doesn’t work, buy a new PCV valve. Remember to get a high-quality replacement from a reputable brand. This ensures that it has the precise calibration for your engine model. Replace it after every 20,000 to 50,000 miles to avoid costly repairs. 

Benefits of changing the PCV Valve

  1. Constant air circulation keeps moisture away
  2. No crankcase emissions
  3. Eliminates excessive carbon buildup, keeping engine safe from catastrophic failure
  4. Protects the engine during a misfire


As seen above, testing a PCV valve is a simple job that you can do on your own. It doesn’t take much time and neither does it require a lot of expertise. I hope this article helped you to know how to test a PCV valve and how to replace one if you need to. Stay tuned for more DIY posts.


How can you tell if a PCV valve is bad?

The best way to tell if a PCV valve is bad is to remove it and shake it. A good working PCV valve will produce a rattling sound. If you do not hear any sound at all, the PCV valve has failed and may no longer be able to open or close.

What happens if PCV valve stuck open?

A PCV valve that’s left open will cause a vacuum leak. The will likely result in drivability issues and surging.

What is the most common problem with PCV valves?

The most common problem with PCV valves is clogging and sludge buildup. This eventually leads to engine damage and expensive repairs. The pressure within the engine increases due to clogging, causing the PCV valve not to open or close as it should.

How long can I drive with a bad PCV valve?

As a rule of thumb, you shouldn’t drive for a very long time with a damaged component. You may get away with about 12 hours of driving if you have a bad PCV valve. However, the excess gases and carbon buildup could cause damage to the engine.

What is the code for a bad PCV valve?

The most common codes that you’ll get when you have a bad PCV valve are P0171 and P0174. It’s good to note that these codes will not mention the PCV valve. They refer to a lean condition in the engine. This is especially if the valve is stuck open.

Can I use WD40 to clean PCV valve?

Yes. You can use WD40 to clean your PCV valve. Simply spray it on both the inside and outside of the valve. This should help remove any sludge that may be blocking it.

How much does it cost to replace the PCV valve?

It costs between $70 and $90 on average to replace a PCV valve. Parts are priced at about $25 while labor ranges between $50 and $65. This is just but a ballpark figure that does not include fees, taxes, and the make and model of the car.