Emission Control Systems: Description and Operation

DESCRIPTION
To reduce exhaust gas emissions, the positive crankcase ventilation system, fuel evaporative emission system, and exhaust system are employed. This system consists of the fuel evaporative emission system, EGR function control system, PCV system, and a three-way catalytic converter. The purpose of these systems is to reduce CO, HO and NOx emissions.


EVAPORATIVE EMISSION CONTROL SYSTEM (EVAP)
Evaporative emission control system consists of the fuel vapor valve and charcoal canister. The evaporative fumes are vented through the fuel vapor valve to the charcoal canister. From the charcoal canister, the evaporative fumes are introduced into the engine and burned.

EXHAUST GAS RECIRCULATION SYSTEM (EGR)

NOTE: This system is only on models with manual transmission.

EGR system recirculates a small amount of exhaust gas into the intake manifold to reduce the NOx emissions. This system consists of the EGR valve, EGR vacuum regulator solenoid, differential pressure feedback EGR sensor, powertrain control module and input devices.

POSITIVE CRANKCASE VENTILATION SYSTEM (PCV)
PCV valve is operated by intake manifold vacuum. When engine is running at idle, valve is opened slightly and a small amount of blow-by gas is drawn in. At higher engine speeds, PCV valve opens further and a larger amount of blow-by gas is drawn in.

THREE-WAY CATALYTIC CONVERTER (TWC)
Catalytic converters promote reactions that change CO, HC, and NOx into carbon dioxide, water vapor, and nitrogen gas respectively. The metals platinum and rhodium are used as catalysts to stimulate the necessary chemical reactions.

INTAKE AIR TEMPERATURE CONTROL SYSTEM (IATCS)
The intake air temperature control system regulates the air temperature entering the engine. The system helps reduce CO and HC by keeping the intake air temperature fairly constant. This reduces varying air density and improves fuel atomization which aids the computerized engine control system in maintaining the air fuel ratio within the stoichiometric window.