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
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.