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 (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.
As the TWC's efficiency degrades, its ability to store oxygen is reduced. This causes higher variations in post TWC exhaust stream oxygen content and results in increased sensor 2 signal activity as shown.
When running the monitor, the ECM compares sensor 1 and sensor 2 signals over a specific time to determine the TWC efficiency. The ECM begins by calculating the signal length for both sensors.