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Question DetailsAsked on 5/22/2013

what is catalyc converter

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2 Answers


A Catalytic Converter is simply put, a part of your exhaust system that converts engine pollutants (like fuel vapors and carbon monoxide) into environmently safe carbon dioxide and water. When you see water coming from a tail pipe, that's the catalytic converter doing its job. Converters are made from a substrate material consisting of precious metals, which is why they are fairly expensive. Some people try to remove the converters, but today's vehicles require them by law and oxygen sensors before and after the converter will not read correctly without them. This will cause the Check Engine light to come on.

Answered 7 years ago by Altcarcare


A catalytic converter (also called cat converter or just cat) is commonly found in gasoline engine cars, though they are also used in a much larger form in some power plants, chemical refineries, etc. Basically a catalytic converter is a tank or canister filled with chemicals, that with the chemical assistance of the Catalyst, cause or promote a chemical reaction. A catalyst is an element or chemical that promotes a reaction, but does not directly tbecome part of it - it facilitates the reaction but does not become part of the final product, and with the exception of very small losses stays within the converter as the reaction goes on.

I will explain how it works in a car, which is probably the context you are asking about. Coming off your engine there is a (typically cast iron) pipe manifold that collects exhaust gas from each cylinder (called the exhaust manifold), that come together into one outlet. That goes into the header, which curves the exhaust gas so it leads back towards the tail of the car. On fancy outfits the manifold and header are deisgned to minimize exhaust flow friction and is just called "the header" by car buffs. 8 cylinder and performance cars typically (but not always) have two headers leading into 2 seperate exhaust systems all the way back to the tailpipe. After the header comes the catalytic converter which generally looks torpedo or canister like (See referenced article in Source, below), and will have at least one oxygen sensor wire coming out of it, except on pre-about 1976 cars that are not required to have one. After that comes the muffler, which reduces the exhaust noise and is usually an oval shaped cylinder, then pipe to the back of the car called the exhaust pipe or tailpipe.

The catalytic converter is filled with granular or porous media (typically ceramic balls or metallic mesh that looks like steel wool) coated with a very thin layer of platinum, palladium, and rhodium. As the exhaust gases pass through the converter, these rare metal are the catalysts that convert unburned gas and nitrous compounds and carbon monoxide into water vapor and carbon dioxide, thereby reducing air pollution. They run VERY hot, which is why you should never park on long grass or spray paint or undercoating near it, as the converter will set fire to it. For more details and pictures see link in source, below. The car has an oxygen sensor that sticks into the cat converter and informs the car's computer about how efficiently it is burning the unburned gas, and if there is not enough oxygen in the exhaust, adjusts the fuel mixture to the engine or sometimes the valve timing. That is the short version of a rather complex interaction.

Because the device is designed to maximize contact of the exhaust gases with the catalytic media, any soot or unburned oil sticks to the media, eventually plugging it and causing it to work less efficiently. Therefore, it periodically needs replacing. Because of the valuable metals in it, which are reclaimed, it has a significant trade in value on a new one - the typical credit or scrap value can run from about $50 for a little 3 cylinder car to over $1000 for a large displacement 8 - 12 cylinder, though typically in the $100-250 range. A replacement may list a credit, or just require a used trade-in of same size and include the credit in the purchase price.

Cat converters. by federal law, have to be warrantied for 8 years of 80,000 miles on a new car (whichever comes first) on vehicles manufactured in 1995 or later. See this link for more info -
Light duty diesels made after 2010 also have to have cat converters, and they are just starting to enact regulations requiring them for heavy duty diesels.
If you live in California, additional stricter rules apply, including having to put a cat converter on cars without them if they cannot pass the periodic emission test.

If your repair shop says the cat converter needs replacing, you are looking typically at $100-250 labor bill (for a csr where it is accessible) on top of catalytic converter cost of about $150-1000 from original manufacturer, $75-400 typically for an after-market one online or from an auto parts store. In some cars, especiallysome foreignn ones, labor can soar to $1000 because you have to remove the transmission or transfer case to replace the cat converter ! If you use an after-market one be aware that your dealership, if you take your car there for repairs, may from that point on refuse to honor the warranty on your emission system if you do not use OEM parts.

If you are told it needs replacement, be sure to check with them that they have tested the oxygen sensor, because if that goes bad it can imply a plugged cat converter when it is actually OK.


Answered 7 years ago by LCD

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