Positive Crankcase Ventilation: Description and Operation

Positive Crankcase Ventilation (PCV) System
The PCV system:
- uses intake manifold vacuum to ventilate blow-by fumes from the crankcase.
- returns the fumes to the intake manifold for combustion.

The PCV valve:
- varies the amount of blow-by gases returned to the intake manifold based on available engine vacuum.
- prevents the entry of combustion gasses backfiring into the crankcase.

The PCV system consists of:
- crankcase ventilation tube
- positive crankcase ventilation valve
- crankcase vent oil separator (2.0L Zetec only)