Circuit Description
WARNING: This page is about a different car, the 2002 Pontiac Sunfire and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
In order to control emissions, a 3-way catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.
The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor (HO2S) 2. The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to effectively convert the exhaust emissions. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front Oxygen Sensor (O2S) 1.