Your car's engine has several features that help it save fuel and run more
efficiently. One of those features is the PCV valve.
The PCV valve is a small one-way valve attached to your engine block,
usually on the top or side of the valve cover. It uses a vacuum hose to
pull unburned fuel and exhaust gases from the engine crankcase back
into the intake manifold.
The PCV valve is important to the health of your car's engine. But,
unfortunately, a bad PCV valve can also cause problems.
PCV Valve Stand For
PCV valve stands for Positive Crankcase Ventilation valve.
Some vehicles have a CCV valve, which stands for Crankcase Ventilation
valve. CCV valves are usually found in older cars.
Even though these two valves have different names, they do the same thing.
What Does A PCV Valve Do
The positive crankcase ventilation valve function is to pull exhaust gases
from the engine compartment to send them back to the intake manifold.
The PCV valve was developed to help cars reduce toxic gases by recycling
some of the exhaust back through the engine to ensure that it burns as much
fuel as possible.
This also helps with fuel efficiency, as well as offering some protection
from the harsh conditions created by running the engine.
When your engine burns air and fuel mixture during combustion, it creates a
lot of pressure.
This pressure can cause "blow-by," which is what it's called when some of
the leftover exhaust gases are pushed past the piston rings of each
These gases get carried past the cylinder wall and into the crankcase.
The crankcase is the bottom area of the engine, where the crankshaft, the
oil pan, and the oil pump are located.
The crankcase ventilation system uses the PCV valve and the natural vacuum
created by the engine to pull the crankcase gases back into the intake
manifold, mixed with fresh air-fuel mixture.
This allows any unburned fuel to be adequately burned off instead of
escaping through the exhaust system.
This process also helps keep the crankcase's internal pressure regulated to
a normal level.
PCV Valve Location
The PCV valve is almost always located on the top of the engine block.
Most PCV valves will be mounted on top of the valve cover. It will be
seated in a rubber grommet with a vacuum line attached to it.
Some PCV valves may not be mounted on the valve cover but will usually be
close to it. The intake manifold is another common location for the PCV
How Does A PCV Valve Work
A PCV valve works by using a one-way valve attached to a vacuum hose.
When you first crank your engine, it has no vacuum present, so the one-way
valve stays closed. This allows your engine control unit to set the right
air-fuel mixture for a smooth idle.
As your engine runs, it creates a vacuum in the combustion chambers.
This natural vacuum causes the one-way valve inside the PCV valve to open,
drawing exhaust gases from the crankcase.
What Happens If PCV Valve Is Disconnected
It is easy to tell if the PCV valve gets disconnected. You will notice a
few symptoms right when you start your engine.
Your car will usually have a higher-than-normal idle, which may cause it to
run roughly right when it first cranks.
If you open your hood while your engine is running, you should hear a loud
"sucking" sound from the engine bay. A vacuum leak causes this.
This sound can be traced to the vacuum hose or vacuum port for the PCV
valve, depending on where it's disconnected.
What Happens When A PCV Valve Fails?
You can tell if your PCV valve begins to fail in several ways.
Problems with your engine idle, misfires, leaks, or increased oil
consumption are all signs of a failing PCV valve.
Bad PCV Valve Symptoms
Since the PCV valve controls an integral part of your engine function, it
can cause several problems if it goes bad.
Here are a few things to watch out for if you think you may have a bad PCV
The pressure that builds up in the crankcase when the engine is running has
to have a place to go. It can force its way out through the gaskets and oil
seals if it doesn't.
This will cause your engine to leak oil. You will notice this oil leakage
from a few common places.
The oil pan gasket and the valve cover gasket are two of the most notorious
places for these oil leaks.
Contaminated Motor Oil
A faulty PCV valve can cause contamination in your motor oil.
The gases pushed into the oil pan contain exhaust and unburned fuel. Since
they are under pressure and in contact with the oil, they can easily be
absorbed into the oil.
If you notice that your oil has a heavy gas smell or is beginning to turn
into dark-colored sludge, this can signify a bad PCV valve.
Rough Engine Idle
The engine control unit adjusts the air-fuel mixture while the engine is
If you have a faulty PCV valve or damaged PCV valve, this will throw off
the mixture and can cause rough idling.
Rough idling, engine stalling, and engine misfires can all be caused by a
bad PCV valve.
Check Engine Light
The PCV valve can cause a check engine light to come on. In addition,
several sensors can be affected by a damaged PCV valve.
An engine misfire will almost always cause a check engine light. Likewise,
misfires can happen when the PCV valve needs to be fixed.
If the air-fuel mixture is incorrect, the oxygen sensor can get a bad
reading. This will also cause a check engine light.
If you have a check engine light that you can't figure out, then check the
PCV valve. It could be the cause.
Oil On The Air Filter
Check the PCV valve if you notice oil stains on your car's air filter.
A defective valve can allow excess engine oil to be drawn into your air
intake. This will show up as oil being blown onto your vehicle air filter.
PCV Valve Oil Consumption
A faulty PCV valve can lead to oil consumption from your engine. Oil
consumption occurs when your engine burns oil in the combustion chambers.
An engine is supposed to have a small amount of oil on each cylinder wall
However, if the crankcase pressure is too high because of a defective PCV
valve, additional oil can be drawn past the piston rings and burned with
the air-fuel mixture.
This will show up in the form of blue smoke from your car's exhaust system.
PCV Valve Stuck Open Symptoms
A PCV valve can become clogged with deposits and get stuck open. This will
cause a few different issues.
The engine computer will read this as a vacuum leak and adjust your fuel
mixture, which will cause your engine to run "lean" or with too much air
and too little fuel.
This will cause rough idling, hard starts, difficulty cranking, or engine
It may also cause stalling or surging while driving since your computer
will send the wrong fuel mixture to your intake manifold.
How To Tell If PCV Valve Is Bad
There are a few ways to test your PCV valve, but the easiest way to tell if
the PCV valve is bad is to listen to the noise it makes.
Remove the PCV valve from the valve cover with the engine turned off. It
will probably be pretty dirty, so wipe it off.
Shake it in your hand for a few seconds, and pay attention to the noise it
makes (or if it makes any noise at all.)
You can also test the PCV valve by disconnecting the vacuum line to see if
it's working correctly.
With the engine running, gently pull off the vacuum line that runs from the
valve to the intake manifold at the manifold end.
You should feel suction on the line when you touch your finger to the end
of the vacuum line. This means that the one-way valve in the PCV valve is
working as it should.
If you don't feel any vacuum suction on the line, this is another sign that
the PCV valve may be clogged or defective.
Bad PCV Valve Sound
A good working PCV valve will make a metallic rattling noise when you shake
A bad PCV valve will make no noise at all.
If your PCV valve doesn't rattle and is quiet when you shake it, there's a
good chance it doesn't work anymore.
How To Clean PCV Valve
You can sometimes fix a clogged PCV valve by cleaning it. This may save you
the trouble of having to buy a new one.
Carburetor or throttle body cleaner are the best solvents to clean the PCV
valve. You can use brake cleaner if available, but it can damage the PCV
Use rubber gloves and safety glasses when using solvents since they can
Remove the PCV valve from the valve cover, and wipe it as clean as
If you don't have a lot of time and want to give it a quick clean, then you
can spray it off with some cleaner and wipe it with a rag or paper towel.
Be sure to let it air dry completely before reinstalling it. Spraying it
with compressed air will help dry it if you have access to it.
The best way to clean the PCV valve is to soak it in cleaner for a bit
Pour carburetor cleaner or throttle body cleaner into a small plastic
container, and submerge the PCV valve in the cleaner. Let it soak for up to
a few hours.
Take the valve out and wipe it off until dry. Let it sit and completely air
dry, or spray with compressed air before reinstalling it.
PCV Valve Replacement Cost
PCV valve replacement is usually not very expensive. The PCV valve costs
around $10 to $15 at most auto parts stores.
Since replacing the PCV valve is easy, you can do it yourself and save
However, if you want to pay a mechanic to do the work for you, you would
pay more labor costs than the cost of the part itself.
You can expect to pay anywhere from $30 to $100 for a mechanic to replace
the PCV valve.
Since this is such an essential part of your car engine, the PCV valve
replacement cost can be considered money well spent.
Since the positive crankcase ventilation valve is a small part, it can
often get overlooked when performing routine maintenance on your vehicle.
This little valve is a big part of what makes your engine run correctly, so
check it regularly.
Taking care of it will help keep your engine running great and your car
driving smoothly for years to come!