Emission Control Systems: Description and Operation

Engine Emission Control

NOTE: Do not permanently remove or render inoperative any part of the vehicle emission control system including related hardware. Failure to comply may violate applicable state and federal laws.

NOTE: The vehicle emission vacuum routing diagrams are contained in the Description and Operation subsection of the Engine Emissions Control system. For additional information, refer to Evaporative Emissions System.

The engine emission control system consists of the:

- EGR system.

- PCV system.

EGR system

The EGR system returns 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 Nitrogen Oxides (NOx) in the exhaust emissions.

The EGR valve:

- is electronically controlled by the PCM.

- is connected to the exhaust manifold by the EGR valve-to-exhaust manifold tube.

- controls recirculated exhaust gas flow to the intake manifold.

- monitors the flow of recirculated exhaust gases through the EGR valve-to-exhaust manifold tube.

- returns a signal to the PCM.

The amount of recirculated exhaust gas depends upon:

- engine rpm.

- intake manifold vacuum.

- exhaust back pressure.

- engine coolant temperature.

- Throttle Position (TP).

PCV system

The PCV system:

- uses intake manifold vacuum to ventilate blow-by vapors from the crankcase.

- returns the vapors to the intake manifold for combustion.

The PCV system consists of the:

- crankcase ventilation tube.

- PCV valve.