Emission Control Systems: Description and Operation

PURPOSE
Emission control systems reduce harmful gases (CO, HC, and NOx) which are by-products of the combustion process. The emission controls have the following major systems:

CRANKCASE EMISSION CONTROL SYSTEM
The crankcase emission control system is a closed-type crankcase ventilation system which prevents blow-by gases from escaping into the atmosphere. Blow-by gases in the crankcase are routed back to the intake manifold for combustion.

EVAPORATIVE CONTROL SYSTEM
The evaporative control system prevents the escape of fuel vapors from the fuel storage and delivery systems into the atmosphere. It consists of various components, which collect and lead the fuel vapors to the intake manifold for combustion.

EXHAUST EMISSION CONTROL SYSTEM
The exhaust emission control system consists of a three-way catalytic converter and some models are equipped with an exhaust gas recirculation system (EGR).

AVAILABLE SYSTEMS
Volvo uses one or more of the following emission control systems on their engines depending on country, state, year model and engine (the specific emission control systems used on your vehicle are listed under "SYSTEM I.D."):

-Three-Way Catalytic Converter (TWC)
-Positive Crankcase Ventilation (PCV)
-Evaporative Control System (ECS)
-Thermostatic Air Control (TAC)
-Exhaust Gas Recirculation (EGR)