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 will reduce fuel economy and engine ventilation. This will weaken engine performance and shorten engine life.

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

The Vehicle Emission Control Information (VECI) decal shows:
^ the components of the emission control system.
^ the correct vacuum hose routing.

The PCV system uses intake manifold vacuum to ventilate the crankcase and return the fumes to the intake manifold for combustion.

EGR System Components:

The EGR system returns a portion of the exhaust gas to the intake manifold to reduce the combustion temperature. This results in lower nitrous oxide formation.

The EGR vacuum regulator solenoid uses input from the PCM to change the EGR valve operation.

The EGR valve-to-exhaust manifold tube:
^ connects the exhaust manifold to the EGR valve.
^ has two tubes connecting to the differential pressure feedback EGR for EGR flow monitoring.

The differential pressure feedback EGR:
^ monitors the EGR flow rate through the EGR valve-to-exhaust manifold tube.
^ sends an EGR flow rate signal to the PCM.

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. The differential pressure feedback EGR measures the flow through the EGR valve from the exhaust manifold tube and sends a signal to the PCM. A metering orifice in the EGR valve-to-exhaust manifold tube restricts the flow rate when the EGR valve is open.

The secondary air system is used to reduce Hydrocarbons (HC) by introducing oxygen into the exhaust gas stream. It operates at startup for the first 90 seconds.