System Description

Catalyst efficiency is demonstrated in its ability to oxidize CO and HC emissions. Engine Control Module (ECM) compares output signals of front and rear Heater Oxygen Sensor (HO2S) to determine whether output of rear sensor is beginning to match output of front HO2S. As catalyst wears, rear HO2Ssignal trace begins to match front HO2S signal trace. That is because catalyst becomes saturated with oxygen and cannot use oxygen to convert HC and CO into H2O and C02 with same efficiency as when it was new. A completely worn catalyst shows a 100% match between front and rear HO2S outputs.