Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
PCV System: Operation
When engine is running at idle, high intake manifold vacuum pulls blow-by gases out of crankcase through PCV valve and into intake manifold where they mix with incoming air/fuel mixture. Fresh air enters crankcase from hose to valve cover on Civic and Prelude, and from hose to breather chamber on Accord.
When engine is running at wide open throttle, manifold vacuum at PCV valve decreases and vacuum in air cleaner increases. As a result a small amount of blow-by gas flows out of the crankcase and into air cleaner.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.