Monitor Description
The vehicle is equipped with the two 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 sensor1 and sensor 2 signals over a specific time to determine the TWC efficiency. The ECM begins by calculating the signal length for both sensors.
Heated Oxygen Sensor Signal Length:
| DTC No. | DTC Detection Condition | Trouble Area |
|---|---|---|
| P0420 | After engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed range, waveforms of heated oxygen sensors have same amplitude (2 trip detection logic) |
|