📖 What It Does
Relieves crankcase pressure caused by combustion gases sneaking past piston rings. Without PCV the crankcase would over-pressurize, blow out seals, and pollute the air.
⚙ How It Works
A small one-way valve in the valve cover or intake manifold uses engine vacuum to draw gases out of the crankcase. The flow rate self-regulates: high vacuum (idle) = low flow; low vacuum (full throttle) = high flow. Fresh air enters through a breather, sweeping vapors through to the intake.
⚠ Symptoms When It Fails
Symptoms include oil leaks from seals or gaskets, whistling at idle, rough idle, P0171/P0174 lean codes, and blue smoke. A stuck-closed PCV over-pressurizes the crankcase. A stuck-open PCV creates a vacuum leak. See full symptom guide.
💰 Replacement Cost
Replacement: $20–$150. The valve is $5–$40. Labor is 5–30 minutes on most engines. Often the cheapest fix in your toolbox. See PCV cost.