Mechanics

Emissions

Step by step guide on how automotive emissions systems work. This article pertains to all vehicles except electric.

Step 1
- The vehicle computer is responsible for the emission produced by the internal combustion engine it controls. By using many sensors such as an oxygen or mass air flow, which provide feedback data for the computer to analyze and adjust engine emissions, which are controlled to within manufacturer specifications.


Main Computer

Step 2 - The exhaust system oxygen sensor is designed to sense the amount of oxygen in the exhaust system and send feedback data to the computer.


Oxygen Sensor

Step 3 - An EVAP (evaporative emission) solenoid is used to purge raw gas vapor from the fuel tank as to not allow these fumes to enter the atmosphere.


EVAP Purge Solenoid

Step 4 - An electronic throttle actuator is designed to move the throttle plate only when the engine can utilize the fuel being consumed. This control helps unneeded emissions when a driver over advances the throttle pedal.


Electronic Throttle Actuator

Step 5 - A catalytic converter is utilized to expend un-burnt fuel in the exhaust system. The unit is heated by exhaust gases as thermo reaction heats up to achieve the design goal of lowering exhaust emissions. By using primary and secondary oxygen sensors the efficiency of the catalytic converter is monitored. An electric air pump is sometimes used to help heat up the catalytic converters to optimize efficiency.


Catalytic Converter

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-22)