­This may look like a simple piece of machinery, but it's part of  a much more complex system in your car.

­To understand why a catalytic converter fails, you need to know how it works. The catalytic converter is part of the automobile exhaust system. It converts harm­ful compounds in exhaust into harmless compounds. In a typical passenger car, the catalytic converter, which resembles a muffler in shape, is between the engine and the muffler. It's on the underside of the car, usually underneath the passenger seat. Maybe you have felt its warmth through the floor on a long trip.

Catalytic converters have been standard on U.S. automobiles since the mid-1970s. The catalytic converter helped drive the push toward unleaded gasoline as well. Leaded gasoline contaminates the catalyst used inside a catalytic converter, destroying its usefulness and leading to a clogged converter.

Go to the next page to see what can go wrong with your catalytic converter.