Catalytic Converter: Description and Operation

Catalytic Converter System Diagram:

Warm up Three Way Catalytic Converter (WU-TWC) Outline
- The WU-TWC is installed to the California emission regulation applicable models.
- The WU-TWC is installed closer to the engine than the regular converter and is warmed up quicker. This enables a chemical reaction to occur at a lower engine temperature.

Catalytic Converter Monitoring
- The PCM uses the HO2S signals to monitor the catalyst system for deterioration.
- Under normal closed loop fuel conditions, the catalytic converter has oxygen storage that makes the rich/lean switching frequency of the rear HO2S slower when compared to the front HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines, and the rear HO2S begins to switch more rapidly, approaching the frequency of the front sensor.
- WU-TWC is monitored for the California emission regulation applicable model. The regular converter (under body) is monitored for the Federal models.
- Front and rear HO2S switches are counted for a predetermined period. A rear-to front HO2S switch ratio is calculated. if the switch ratio is grater than the threshold, the PCM determines the catalyst has failed.