Clean Air & Good Mileage
The catalytic converter and oxygen sensor, along with the computer are key components in keeping your car's exhaust emissions within specifications to reduce air pollution and give you better fuel mileage.
The catalytic converters are bolted or welded into the exhaust system. Your vehicle may have as many as 4 separate converters, but most cars have two. There is one close to the engine called the primary converter and one back further in the exhaust and it is called the secondary converter. The catalytic converters change or convert the gases in the exhaust system into a less harmful type that won't pollute the air as bad. They contain a special metal inside that uses the heat from the engine to re ignite the unburned gasoline that remains in the exhaust. These special metals wear out with age or they are damaged if the engine runs poorly and dumps an excessive amount of gasoline into the exhaust.
The oxygen sensors bolt into the exhaust system or the catalytic converters and send a voltage signal to the computer telling it how much oxygen is in the exhaust, which is an indication of how mush unburned fuel remains in the exhaust. The computer will then adjust the fuel mixture and timing in order to reduce the air pollution and give you better fuel mileage. The O2 sensors wear out with age or are damaged by a rich running engine or vehicle that runs poorly.