Three-Way Catalyst Oxygen Storage Capacity

Three-Way Catalyst Oxygen Storage Capacity:

The PCM must monitor the TWC system for efficiency. In order to accomplish this, the PCM monitors the pre-catalyst and post-catalyst HO2S. When the TWC is operating properly, the post-catalyst (2) HO2S shows significantly less activity than the pre-catalyst (1) HO2S. The TWC stores oxygen during the normal reduction and oxidation process. The TWC releases oxygen during the normal reduction and oxidation process. The PCM calculates the oxygen storage capacity using the difference between the pre-catalyst and post-catalyst HO2S voltage levels.




Whenever the sensor activity of the post-catalyst (2) HO2S nears the sensor activity of the pre-catalyst (1) HO2S, the catalysts efficiency is degraded.
Aftermarket HO2S characteristics may be different from the original equipment manufacturer sensor. This may lead to a false pass or a false fail of the catalyst monitor diagnostic. Similarly, if an aftermarket catalyst does not contain the same amount of precious metal content as the original part, the correlation between oxygen storage and conversion efficiency may be altered enough to set a false DTC.