Catalyst Monitor (Bad Catalyst)
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
A degraded TWC catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the post-catalyst heated oxygen sensor (2). The degraded catalyst post-catalyst HO2S output voltage will therefore appear similar to the typically active output voltage of the pre-catalyst heated oxygen sensor (1).