Positive Crankcase Ventilation System (PCV): Operation, Malfunctions, and FAQs

Positive Crankcase Ventilation System (PCV): Operation, Malfunctions, and FAQs

The positive crankcase ventilation (PCV) is a feature  in piston engines that maintains regulated pressure ratios in the crankcase in relation to the surrounding environment.  A further function is the accumulation and environmentally friendly discharge of the gasses produced in the engine.

What is a PCV valve

This is a part which is most often located at the valve cover, but you could also find it somewhere between the intake manifold and the crankcase air outlet. It utilises the engine vacuum to pull out the blow-by gasses out of the crankcase and then push them into the intake manifold and into the combustion chambers where they can be burned-off again.

Symptoms of malfunction 

 Bad pcv valve symptoms

Problems can arise due to a stuck open, or stuck closed valve. You may suspect that there is a problem if you begin noticing the following symptoms. There is an increase in the internal engine pressure, the gaskets or some of the oil seals fail to work and black smoke is emitted. You may notice that the engine leaks oil or surges, that there is a build-up of sludge, or you get an MAF trouble code, among others.

How to check

Take a look and see if all the rubber parts and hoses are in working condition. Change the mesh filter under the valve. Take out the valve and shake it — if it rattles, it’s fine – if it doesn’t you have to replace it.

What is a crankcase breather and what does it do

When the engine is on, a quantity of “blow-by” gasses is emitted into the crankcase through the piston rings. These gasses then result in a pressure build-up in it which, if left unattended, can cause serious problems such as leaking seals, oil burn or even engine damage. In summary, it is the external component of the engine that is responsible for the ventilation of the crankcase and is where the engine oil is stored.

If you notice the following, you know that there is an issue that has to be taken care of:
The engine doesn’t run smoothly or jerks – especially when cold. The speed fluctuates at idle or even stalls. You may notice your check engine light turning on, but later turn itself off again or you may see oil dripping from the crankcase. 


Repair pcv

The exact repair process depends on the type and accessibility of the engine. In most cases, various components such as the air filter box and the throttle valve must be dismantled first. It is important to know that not all components of the crankcase ventilation system have to be replaced. Often it is enough to replace only the crankcase ventilation valve. Look for cracks or hoses that may have come loose, faulty electrical connections, defective valves, and blockages due to mud. If the cause of the problem is a defective crankcase ventilation pipe, it should always be checked carefully whether plastic residues can still be found in the intake area. Otherwise, this can lead to expensive subsequent damage.


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