Catalytic converters use devices which use precious metals, typically platinum and palladium, to alter the harmful gasses created by combustion and make them less dangerous. They do this by forcing exhaust gasses to pass through a chamber containing these metals, either in a honeycomb structure or beads. The molecules in the exhaust gas make contact with the catalyst (platinum, palladium, rhodium, etc) and their atomic structure is altered when they do. This interaction only occurs at a very high heat level, however, so a cold catalytic converter is doing pretty much no work at all!
Catalytic converters can build up carbon over time, reducing their throughput and eventually causing them to stall the engine, reduce fuel economy, overheat and in extreme circumstances cause fires. There will be plenty of tell tale signs before a fire breaks out, however. In California a failing catlytic converter could cause even more headache due to the strict emissions requirements and smog tests.
Replacing a catalytic converter using "direct fit" cats will usually entail a few bolts and a couple gaskets. Some "universal fit" converters will require welding in order to get them installed.
We stock and sell a wide variety of quality catalytic converters from these manufacturers: