Auto Repair For Dummies, 2nd Edition
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Not every vehicle has a PCV (positive crankcase ventilation) valve. If yours has one, and your engine has been idling roughly or a malfunction indicator light goes on, check the PCV valve to make sure it isn’t clogged with sludge from the contaminants in the exhaust fumes or stuck in the wide-open position.

The PCV valve is a vital part of the emissions control system on most vehicles. The PCV valve is usually plugged into a rubber grommet in the valve cover, as shown here:

A PCV valve located in the valve cover. A PCV valve located in the valve cover

It may be located on or near the intake manifold, as shown here.

A PVC valve located on the valve cover, with the hose that leads to it removed. A PVC valve located on the valve cover, with the hose that leads to it removed

A hose leading to the PCV valve is often kept in place by a clamp. Sometimes there’s a little L-shaped housing on the end of the hose that covers the end of the valve.

Car manufacturers suggest that PCV valves be cleaned or replaced somewhere between 20,000 to 50,000 miles of driving. Consult your owner’s manual to see where the PCV valve is located on your vehicle and what the recommended service intervals are.

The valve is usually replaced during scheduled tune-ups, but depending on its type and location, you may be able to check, clean, and replace it yourself.

There are different ways to check whether your PCV valve is functioning properly, including the two below. Pick the one that seems easiest for you. (The engine should be idling no matter which method you choose.)
  • Method 1: Remove the PCV valve from the valve cover with the hose still attached. Then place your finger over the open end of the hose. If the valve’s working well, you will feel strong suction. Try shaking the valve. If it’s unobstructed, it should rattle. If it’s fouled, the rattle will be indistinct or non-existent.

    One way to check your PCV valve. One way to check your PCV valve

  • Method 2: Remove the cap from the oil filler hole on the valve cover and place a stiff piece of paper over the opening. If your PCV valve is working properly, the paper should be sucked against the hole within seconds.

If the valve doesn’t seem to be working properly, before you go to the trouble to replace it, try cleaning it to see if that makes a difference.

Clean it yourself by immersing it in carburetor cleaner. There should be no gummy deposits or discoloration on a clean valve. If your PCV valve must be replaced, buy a new valve, remove the old one, and insert the new one in its place.

Replacing a vehicle's PCV valve

Follow these instructions to remove your vehicle’s PCV valve in order to check, clean, or replace it with a new one:

  1. Locate the PCV valve and loosen the hose clamp if there is one, or pull the little L-shaped housing off the end of the valve.

  2. Remove the valve.

    Some PCV valves are held in place with a rubber grommet and can just be pulled free. Others are threaded into place. If you can’t unscrew the valve by hand, try to grasp its base with the open end of a combination wrench or a small crescent wrench.

  3. Check the hose and the hose clamps or grommet.

    Remove the hose and blow through it. If the hose is dry, brittle, soft, spongy, or full of sludge or hard deposits, you should replace it. If the clamps are rusty or the grommet looks deteriorated, you should replace them, too.

  4. Screw in the new valve.

    If the new valve screws into place, do this by hand to avoid stripping the threads in the valve cover. Make sure that the valve is seated securely (it should stick just a little when you try to unscrew it again), but don’t over-tighten it!

  5. Reconnect the hose to the PCV valve.

    Start the engine, and check around the PCV valve for leaks.

About This Article

This article is from the book:

About the book author:

Deanna Sclar is an acclaimed auto repair expert. She has appeared on hundreds of radio and TV shows, including NBC's Today show and the NBCNightly News. Sclar lectures internationally on the ecological impact of vehicles and is active in promoting residential solar energy programs. Sclar is also the author of Buying a Car For Dummies.

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