How do I know if my catalytic converter has failed?

After the engine exhaust gases pass through the catalytic converter, the gases go through the muffler or mufflers, depending on the make of the automobile. Some vehicles use a pre-converter as well, to perform a similar function. The catalytic converter generally lasts the life of the automobile and rarely has a problem with being clogged or plugged during its lifetime.

The inside of the catalytic converter is a honeycomb set of passageways or small ceramic beads coated with catalysts. A chemical reaction takes place to make the pollutants less harmful. There are many passages for the exhaust gases to flow, to allow for the maximum amount of surface area for the hot gases to pass.

The catalysts include:

Many states and localities have legislated annual automobile emissions testing that checks the actual emissions content. The exhaust emissions test checks for the absence of a converter or a malfunctioning one during an inspection. It's illegal in some states and localities to remove a factory-installed catalytic converter. A mechanic can sometimes temporarily remove it and replace the catalytic converter with a test pipe, but the rules on this can vary from place to place.

So how do you know for sure if your catalytic converter has failed? Get the answer on the next page.

There are two ways a converter can fail:

There really is no "inspection port" for the consumer or mechanic to see an actual clog in a converter. Often, the only way to tell if a catalytic converter is malfunctioning (plugged) is to remove it and check the change in engine performance. When a clogged converter is suspected, some mechanics temporarily remove the O2 sensor from the exhaust pipe ahead of the catalytic converter and look for a change in performance.

A catalytic converter relies on receiving the proper mix of exhaust gases at the proper temperature. Any additives or malfunctions that cause the mixture or the temperature of the exhaust gases to change reduce the effectiveness and life of the catalytic converter. Leaded gasoline and the over-use of certain fuel additives can shorten the life of a catalytic converter.

A catalytic converter can also fail because of:

­Sometimes you can tell that a converter is clogged because you don't go any faster when you push the gas pedal. Also, there usually is a noticeable drop in gas mileage associated with a clogged catalytic converter. A partially clogged converter often acts like an engine governor, limiting the actual RPMs to a fast idle. A totally clogged converter causes the engine to quit after a few minutes because of all the increased exhaust back pressure.

The catalytic converter, like the rest of the emissions system, typically has a warranty length that exceeds the term of the warranty for the rest of a typical U.S. automobile.

Here is a safety reminder: Do not park your car over tall grass or piles of dry leaves. Your car's perfectly running catalytic converter gets very hot -- enough to start fires! You can keep it running well by keeping the ignition system in top shape, to prevent any unburnt fuel from entering the catalytic converter.