Monitor Description
The vehicle is equipped with the two heated oxygen sensors (O2S). One is mounted upstream from the three-way catalytic (TWC) converter (front heated oxygen sensor "sensor 1"), the second is mounted downstream (rear heated oxygen sensor "sensor 2"). The catalyst efficiency monitor compares the sensor 1 and 2 signals in order to calculate TWC ability to store oxygen.
During normal operation, the TWC stores and releases oxygen as needed. This results in low oxygen variations in the post TWC exhaust stream as shown in Fig 1 and Fig 2 .