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PCV Valve problems, fixes

PCV valve

Although the PCV system is generally very simple, there are still things that can go wrong with it. We explained how the positive crankcase ventilation system works earlier in our PCV 101 article. Now let's talk about maintenance, diagnostics, and repair/replacement.

PCV Maintenance

Most vehicles have a recommended replacement interval for the PCV valve. This will range from 50,000 to 100,000 miles and often coincides with the timing belt interval. Some owner's manuals will recommend full replacement, some will recommend cleaning, and some will recommend "inspection." It's very likely that you'll have to replace the PCV valve at the interval, however, as this is usually when buildup has begun to affect the valve's ability to operate.

On newer vehicles - those made after OBD II was implemented and the 2002 OBD II PCV standard was added - will have error codes specifically related to crankcase ventilation.

In general, if your car has any type of sludge buildup or has often gone extra-long on its oil changes, there's a good chance your PCV valve has buildup.

Common Problems With the PCV

Aside from a plugged valve, other problems could be restricted flow through any of the PCV system's connections, especially the vacuum and outlet into the intake.

Leaking main gaskets on the engine block could also be an indication that the PCV system is not operating correctly and is not relieving pressure in the crankcase. If the PCV valve sticks, the crankcase will have nowhere to vent and will begin to build up sludge and put excess pressure on the seals.

The most common symptom of a problem with the PCV system is a noticeable drop in fuel economy and a rough idle. This can be caused by the PCV valve sticking open, breaking its spring, or sticking shut, which raises vacuum pressure in the rest of the intake.

The opposite can also be an issue. If the inlet from the valve to the intake begins leaking, it will allow un-metered air into the intake, creating a vacuum leak.


Most of these will require replacement of the PCV valve or its connectors. Or both. Beware of cheap replacements, however, which can work well for a little while and then begin to have issues well before their interval is up.

Several checks can be done to see if the PCV valve has problems. Start while the engine is idling by putting your finger over the end of the valve (its vent) to see if there is vacuum. If not, something is plugged. A flow tester can give you more information and check to make sure that the PCV valve is performing to spec.

If everything seems OK, but you have a problem, remove the valve and shake it. If it rattles, the pintle is free and should be allowing flow. So you likely have a bad spring or buildup slightly restricting movement inside.

A final check is to measure vacuum in the crankcase. If vacuum is low or non-existent, you should check all of your case seals including the oil pan and others.