Emission Control Systems: 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 system returns a small amount of exhaust gas into the intake manifold. This reduces the overall combustion temperature. Cooler combustion temperature provides a significant reduction of Oxide Nitrogen (NOX).

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.

The amount of recirculated exhaust gas depends upon:
- engine rpm.
- intake manifold vacuum.
- exhaust back pressure.
- engine coolant temperature.
- throttle position.

Exhaust Emission Control System
The exhaust emission control system is listed on the vehicle emission control information (VECI) decal located on the hood).







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 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.