How to test pcv valves

Written by c. taylor
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How to test pcv valves
Regularly check PCV valves to avoid damage to your engine. (engine image by goce risteski from

The purpose of positive crankcase ventilation (PCV) valves is to return unburned hydrocarbons and carbon monoxide into the crank case, so they may be burnt off the second time through. This results in cleaner emissions and reduces moisture and corrosive gases in the crank case. Clogged PCV valves may cause your engine to idle roughly with reduced fuel efficiency. You may also notice the darker-coloured, less-effective oil, which lubricates your engine. To prevent problems associated with clogged PCV valves, you should regularly check the valves and replace any defective ones.

Skill level:

Things you need

  • Needle-nose pliers
  • Rag

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  1. 1

    Locate the PCV valve by looking at the top of your engine for a small hose that attaches to the top of the engine's valve cover or intake manifold. These are large, rectangular parts sitting on the top of the engine, which may also be attached to the oil filter cap.

  2. 2

    Crank the engine so that it is idling.

  3. 3

    Place a rag over the hose leading to the PCV valve and clamp the needle-nose pliers over the rag-covered hose. Clamp hard enough to pinch the hose shut. The engine's idle speed should drop noticeably if the valve is good.

  4. 4

    Pull the PCV valve out of the valve cover and shake it. An unclogged valve will rattle. Pulling the value out may require gentle use of the pliers, but you might be able to just use your hands.

  5. 5

    Place your finger over the opening and feel for suction. If you feel suction, the valve is working properly.

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