Emission Control Systems: Description and Operation: Description and Operation

CAUTION: Do not remove any part of the engine emission control system. Operating the engine without the engine emission control system intact will reduce fuel economy and engine ventilation. This will weaken engine performance and shorten engine life.

The engine emission control system consists of the:
^ Positive Crankcase Ventilation (PCV) system.
^ Exhaust Gas Recirculation (EGR) system.

Exhaust Gas Recirculation
The EGR systems return a small amount of exhaust gas into the intake manifold. This reduces the overall combustion temperature. Cooler combustion temperatures provide a significant reduction of the Oxides Of Nitrogen (NOx) in the exhaust emissions.

The Powertrain Control Module (PCM) controls the EGR vacuum regulator solenoid. The EGR vacuum regulator solenoid controls the vacuum to the EGR valve. When the EGR valve opens, exhaust gas flows to the intake manifold to be returned to the combustion cycle. The differential pressure feedback EGR sensor monitors the flow and returns a signal to the powertrain control module (PCM).

The amount of recirculated exhaust gas depends upon:
^ engine rpm
^ intake manifold vacuum
^ exhaust backpressure
^ engine coolant temperature
^ throttle position

Exhaust Emission Control System
The Vehicle Emission Control Information (VECI) decal is located on the upper radiator support and shows:
^ components of the emission control system.
^ the correct vacuum hose routing.
^ the color stripe of the vacuum hoses.

Positive Crankcase Ventilation (PCV) System
The PCV system uses intake manifold vacuum to ventilate blow-by fumes from the crankcase and return the fumes to the intake manifold for combustion. The positive crankcase ventilation valve (PCV valve) varies the amount of blow-by gases returned to the intake manifold based on available engine vacuum. The positive crankcase ventilation valve also prevents the entry of combustion backfiring into the crankcase.