Emission Control Systems: Description and Operation

PURPOSE
Effective control of vehicle emissions is necessary to reduce the automobile's contribution to environmental pollution.

Emission systems control tailpipe emissions (CO, HC, and NOx), hydrocarbons produced by evaporating fuel, and combustion gases that escape through the crankcase into the atmosphere.

Computerized Engine Controls (CEC)
The computerized engine control system is made up of an electronic control unit (ECU), various sensors, and output devices. This system controls engine operation (i.e. A/F mixture, idle speed and ignition timing), reducing pollutants while maintaining optimum driveability and reducing fuel consumption.

Crankcase Control System (PCV)
The crankcase emission control system is a closed-type crankcase ventilation system, which prevents blow-by gases from escaping into the atmosphere by routing the gases back to the intake manifold for combustion.

Evaporative Control System (EVAP)
The evaporative control system prevents the escape of fuel vapors from the fuel storage and delivery systems into the atmosphere. It consists of various components, which collect and introduce captured fuel vapors into the intake manifold for combustion.

Exhaust Control System (TWC)
The catalytic converter effectively changes harmful pollutants (CO, HC, and NOx), from the exhaust system, into carbon dioxide and water.

Fillpipe Restrictor (FR)
To prevent the introduction of leaded fuel to the system, a fillpipe restrictor is installed. This prevents the larger diameter fuel nozzles used for leaded fuels from entering the fillpipe. Leaded fuel will permanently contaminate the oxygen sensor, and the catalytic converter.