Oxygen Sensor (Down)
Oxygen sensors installed at the front and rear end of the catalytic converter deliver the ECM the current and voltage varying by the oxygen concentrations in emissions.
The front sensor (up) is a linear lambda sensor that controls fuel volume by measuring the oxygen concentrations in emissions. It calculates the oxygen concentration (lambda (λ) value) by reading the amount of current change.
The rear sensor (down) is a multi-layered-thin-film sensor made of Zirconia and Alumina. The sensor calculates the oxygen concentration based on the amount of voltage change generated by the gap between the oxygen concentrations of air and those of emissions.
Both front and rear oxygen sensors are equipped with a heater (heating wire) to rapidly boost up and maintain temperature at the normal operation point. The heating wire is controlled by the PWM through the ECM.