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Do I really need to replace my faulty catalytic converter?

The dealer says my "cat" is dead and a new one is going to cost $1,500. Do I need it? – Randy

Yes, every passenger vehicle sold in the past 35 years is required to have a "cat" – the catalytic converter used in the exhaust system to reduce harmful emissions and allow the vehicle to pass mandatory smog tests.

The catalytic converter became standard equipment on most new vehicles starting in 1975 and was mandatory by 1981 when it was fitted to vehicles for sale in the United States, enabling them to meet newly introduced emission regulations.

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According to the International Platinum Association, catalytic converters get credit for "rendering more than 12 billion tonnes of harmful gasses harmless, worldwide."

This unit, which looks much like a muffler, is filled with exotic materials like platinum, palladium or rhodium used to convert harmful carbon monoxide, hydrocarbons and oxides of nitrogen to harmless carbon dioxide, nitrogen, oxygen and water.

These Platinum Group Metals (PGMs) are the reason for the expense – but also for the cleanliness of the exhaust in modern vehicles. PGMs are physically, chemically and atomically similar and grouped together as elements on the periodic table. They occur together in nature and can be produced from the same ore mined in South Africa, Russia, the United States and Canada.

But they are called precious metals for a reason. Extracting them is a highly labour intensive process, taking up to three months, and 7 to 12 tonnes of ore is needed to produce one measly troy ounce (31.135 grams) of platinum.

The "cat" is designed to expose the maximum amount of surface area of the PGM to the exhaust gasses speeding through. It acts as a second engine, using fuel and oxygen to "light off," burning off much of the harmful components in the exhaust stream.

The "cat" works only at very high temperatures. When an engine is first started from cold, the "cat" does very little to reduce harmful emissions. For this reason, it is placed as closely as possible to the combustion chamber so the hot gasses get to it and heat it as quickly as possible. In some cases the "cat" is preheated using electricity.

Depending on the engine and exhaust configuration, a vehicle can have more than one "cat". While catalytic converters require no maintenance during the expected life of a vehicle, they can be damaged by leaded fuel and some additives, which gather on the ceramic coating and render them useless.

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A broken or failed "cat" will not harm the vehicle, but they are required by law. Replacement prices run from a few hundred to a couple of thousand dollars.

Do you have car maintenance or repair questions? E-mail us: globedrive@globeandmail.com

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