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Car and Truck Catalytic Converters

Cars and trucks in the U.S. have had catalytic converters since 1975. These components have been cleaning toxic gases out of engine exhaust ever since. At times, they must be replaced so your vehicle will run smoothly and pass its emissions test.

What is a catalytic converter?

These devices are components of the exhaust systems of automobiles and trucks. Both gasoline and diesel vehicles have converters. When fuel is burned by the engine, it produces polluting gases in the exhaust. The purpose of the converter is to induce a chemical reaction that changes the toxic gases to cleaner emissions.

What kinds of catalytic converters are available?

There are three types of converters: two-way, three-way, and diesel. The two-way, or oxidation type, is used on cars that were manufactured before 1981 and some diesel engines. They convert carbon monoxide and hydrocarbons into carbon dioxide and water.

The three-way, or oxidation-reduction type, is used on cars manufactured since 1981. Along with the functions of the two-way converter, the oxidation-reduction type also converts nitrogen oxide to nitrogen and oxygen.

Diesel engines may use a diesel oxidation catalyst or a combination of a two-way type with a particulate filter. Which system is used on a specific model depends largely on its year of manufacture.

How do you know when to replace a catalytic converter?

Most people find out they need to replace this part when their vehicle doesn't pass its state-mandated emissions test. If you buy new vehicles and trade them in frequently, you may never need a new converter since they can last for years. If you keep your vehicles longer or buy them used, the component will eventually become clogged or start to leak exhaust gases.

Another sign is if your check-engine light comes on. You may also notice that your mileage per gallon has noticeably dropped. Slower acceleration and overall performance are also signs that you need to replace the converter.

How do you choose a replacement converter?
  • First, find out what factory system your vehicle has. There are two choices: the EPA standard or the California standard, called CARB. This information is on a sticker under the hood.
  • Second, find out whether the state your vehicle is registered in follows the EPA or the CARB standards. The DMV can give you this information. The replacement parts you use will need to meet whichever emissions standard the state requires.
  • Third, check to see if there is an aftermarket part that is made to fit your automobile or truck. These are referred to as “direct-fit.” They will meet all the specs of your model’s exhaust system and will be relatively easy to install. Unfortunately, they are not available for all models. If you cannot get a direct-fit part, you can find a universal converter. The universal models are categorized by the weight and engine size of the car or truck they will fit. Installing a universal type usually requires measuring, cutting, and welding to integrate the component correctly into the rest of the system.