What Is the Catalytic Converter and What Does It Do?

Your vehicle’s exhaust system has a series of components to muffle the noise of your engine and reduce emissions. One of the most important parts for emissions reduction is a catalytic converter. Discover what is a catalytic converter, what it does, and signs that you may need your catalytic converter serviced or replaced.

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What is a Catalytic Converter?

Your catalytic converter, sometimes called the cat, uses a catalyst to convert the more harmful compounds of your engine’s emissions. Typically, a combustion engine emits numerous harmful compounds. In order to protect the environment and prevent you and your family from being exposed to poisonous gases, every vehicle is required to have a catalytic converter in the emissions system.

The catalyst in your converter is typically made of palladium, rhodium, and platinum. These rare metals coat a ceramic interior, which is typically in a honeycomb or bead shape, and converts harmful gases into less harmful emissions.

Typically, your catalytic converter converts approximately 90% of emissions, but there are a number of factors that can increase or decrease the efficiency. Converters are less efficient at converting cooler temperature emissions, so a diesel fuel or short driving distances may reduce the efficiency of your converter.

A particulate filter can be added to catalytic converters to increase the efficiency to 99% by catching ultra-fine particles. Some OEM converters use a particulate filter, and many aftermarket options include this additional component.

Where is the Catalytic Converter?

Your converter is part of your exhaust system. It’s located between the intake manifold and your muffler. The exact configuration depends on the make and model of your vehicle and the exhaust system setup. Many vehicles today have multiple catalytic converts, as do any vehicles with dual exhaust, or partial dual exhaust as most V6 and V8 engines are.

Harmful Emissions It Converts

As your internal combustion engine propels your car forward, it emits three main gases as a byproduct. Each of these gases are harmful either to your health, the environment or both. These are the three main compounds typically emitted by your engine:

  • Nitrogen oxides
  • Carbon monoxide
  • Hydrocarbons

So, what does a catalytic converter do? Your catalytic converter converts carbon monoxide into carbon dioxide, hydrocarbons into carbon dioxide, and water and nitrogen oxides into nitrogen and oxygen.

Nitrogen oxides and hydrocarbons are both causes of smog in the environment. A buildup of nitrogen oxides can create acid rain. Carbon monoxide is a poisonous gas that can be harmful or even fatal if breathed in.

What are the Signs of a Failing Converter

Under normal operations, you can expect your converter to last up to 10 years or more. However, as your vehicle ages, engine symptoms can occur that can cause your converter to fail, or the outside elements can finally cause failure. Here are some common signs of a damaged or inefficient converter:

  • Excessive heat under your vehicle
  • Foul, sulfuric smells from your exhaust
  • Rattling noises from the exhaust, or exhaust leaks
  • Reduced engine performance and acceleration

These signs may point to a clog or damage to the internal structure. Over time, the honeycomb catalyst in your converter can become clogged or break up. This will not only reduce the efficiency of your catalyst but can completely stop exhaust gases from exiting your exhaust system. Once the catalyst is completely clogged, your engine may stall or extremely poorly as the exhaust has no way to exit the system.

Also, the elements of salt and corrosion can wear away at the outside of a converter, no different than a muffler. In many cases, the converter’s protective heat shield is the first thing to go, which can cause a rattling in and of itself, while the entire casing of the converter can rust – no different than a muffler, and cause a bad exhaust leak.

Cleaning Your Catalytic Converter

While there is a handful of methods, theories, and materials out there to physically clean your catalytic converter – from running items through your fuel system, ingested into the intake, or physically removing your catalytic converter from the vehicle and cleaning it in a solution bath, it’s noted that none of these methods are proven to work 100%.

While many gas tank additives can help in greatly reducing emissions, attempting to fix a converter that has completely failed from restriction is extremely difficult and in most cases, changing the converter out with a new unit is the best method for repair. A converter whose catalyst element is damaged, of course, should also be immediately replaced. In all of these cases, the team at AutoZone can help with repairs, advice, or new parts.

Do I Even Need a Catalytic Converter?

Since 1975, a catalytic converter has been required in all US vehicles. If you need to replace your catalytic converter be sure you choose a converter certified by the EPA. Operating your vehicle without a converter or with a faulty converter can be dangerous and illegal for on-road use.

Can I Upgrade My Converter?

A damaged catalytic converter needs to be replaced promptly. However, there are also some benefits of replacing your existing converter, even if it’s functioning properly. An aftermarket catalytic converter provides you with a number of performance benefits in connection with other aftermarket tune-ups.

However, don’t expect a high-flow catalytic converter to provide exceptional performance benefits alone. An aftermarket converter is a great investment if your high-performance vehicle has other aftermarket components that have increased your horsepower 20% or more above OEM levels.

While some aftermarket options may have a longer warranty, many options may not be as cost-effective as an OEM replacement. Ask a knowledgeable AutoZone associate to determine whether your car needs a new converter and whether to upgrade to an aftermarket option or stick with a reliable OEM option.

Find Out More and Shop for a New Catalytic Converter Today

If you have more questions about this essential exhaust system component, or you need assistance in selecting the best replacement converter for your vehicle, don’t hesitate to talk with an associate at your local AutoZone, or check out one of our preferred shops in your area that can help with the repair and diagnosis.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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