What Does a Catalytic Converter Do in a Car?
Catalytic converters reduce harmful vehicle emissions by converting the most toxic compounds into less harmful gases.
Written by John Davis
Reviewed by Georgina Grant
The catalytic converter is an essential piece of your car's exhaust system. Its purpose is to reduce the harmful emissions that escape your vehicle's tailpipe into the atmosphere.
Car engines create lots of harmful gases as byproducts of regular operation. To reduce air pollution and cut down the toxicity of exhaust emissions, the Environmental Protection Agency (EPA) began mandating that all new cars be produced with catalytic converters starting in 1975. But what exactly is a catalytic converter?
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What is a catalytic converter, and how does it work?
Since 1975, all modern cars have been built with catalytic converters. These ingenious parts use high temperatures and precious metals in a "catalyst" chamber to convert toxic compounds into less harmful exhaust gases.
The catalytic converter is located beneath the car, around the middle of its exhaust system. One end connects to the engine—the harmful gases, like hydrocarbons, carbon monoxide, and nitrogen oxides, enter the converter here—and the other end connects to your car's exhaust pipe or muffler. The pollutants blow through the catalyst and are converted into less harmful molecules, like oxygen, nitrogen, and carbon dioxide.
Catalytic converters look like large metal boxes. Inside, there is typically a piece of ceramic covered with precious metals like platinum, palladium, or rhodium. These metals are the catalysts that create the chemical reactions necessary to convert harmful substances into less harmful emissions.
The ceramic inside the converter usually has a honeycomb structure. This allows the gases to flow more easily through the converter.
There are two main types of catalysts found in catalytic converters:
- Reduction catalysts cut down on nitrogen oxide emissions by splitting the compound into nitrogen and oxygen, which are harmless.
- Oxidation catalysts convert carbon monoxide into carbon dioxide by adding oxygen.
Usually, at least one oxygen sensor is attached to the catalytic converter. These sensors analyze the oxygen content in the vehicle exhaust and send that data to the car's electronic control unit (ECU). There, the information is used to help the vehicle run more efficiently by managing the engine's air/fuel ratio.
Key Takeaway Catalytic converters reduce the pollution your car spreads by converting harmful compounds into less toxic gases.
What are the different types of catalytic converters?
There are two main types of catalytic converters. Depending on the year your car was built, it may have one or the other. The two different kinds of catalytic converters are:
- Two-way. These converters were installed on American vehicles until 1981. They use oxidation catalysts, which convert carbon monoxide to carbon dioxide. The hydrocarbons, which are partially burned fuel, are converted to water and carbon dioxide.
- Three-way. These converters have been in use since 1981. They use the same system as two-way converters but also have a reduction catalyst.
Vehicles with diesel engines have special catalytic converters to deal with the emissions of burning diesel fuel.
Catalytic converter theft
Catalytic converters are a frequent target of theft, with incidents up over 400% since 2019. A new catalytic converter could cost you well over $2,000 if yours is stolen. Because of this, you must take precautions to minimize your risks of being robbed.
Why do people steal catalytic converters?
People steal catalytic converters for money. The precious metals that are used to build converters are highly expensive. And the global supply chain crisis has only increased the demand for these materials.
Skilled thieves can remove a catalytic converter from your car in minutes. And with the prices of the precious metals at more than $1,000 per ounce, there is no shortage of scrapyards willing to pay for used converters.
How do you know if your catalytic converter has been stolen?
If your catalytic converter is stolen, you'll most likely notice it immediately. That's because thieves simply cut the converter off the exhaust pipe, leaving a gap between your muffler and the rest of the exhaust system. When you drive your car this way, you—and everyone around you—will notice the deafening sound produced by operating an internal combustion engine without a muffled exhaust.
Additionally, your car will probably detect something wrong with the exhaust system, and you will probably notice a Check Engine light on your instrument panel.
How can you prevent catalytic converter theft?
Thieves routinely target vehicles with expensive catalytic converters, like hybrids. Toyota Priuses are the most popular target, but cars with high ground clearance, like trucks and SUVs, also regularly have their converters stolen.
You can prevent catalytic converter theft and protect your vehicle by taking a few steps:
- Park in a well-lit, populated area. A parking lot with security cameras is ideal.
- Install a protective device on your car. Quality deterrents, like cages that surround the converter, can be pricey. But replacing a stolen catalytic converter will dwarf the price to protect the original part.
- Install a vibration-triggered alarm on your car. These security systems go off when they detect vibrations. Someone sawing off your converter will trigger these alarms.
Other common catalytic converter problems
Besides theft, there are some other problems that you may encounter with your catalytic converter. The converter could malfunction due to age or damage and cause various issues for you and your car. These are the common symptoms of a faulty catalytic converter:
- Poor fuel economy. A clogged catalytic converter can reduce the airflow through your engine. The engine may burn more fuel to compensate, which can result in decreased fuel efficiency.
- A Check Engine light. While a Check Engine light can mean many things, a malfunctioning catalytic converter can cause an incorrect air/fuel mixture, triggering the light.
- Sulfer (rotten eggs) smell. Damage to the catalytic converter can cause it to improperly convert the gases, which may result in a rotten egg smell.
- Trouble starting the engine. If your converter is clogged, the exhaust pressure may increase. This can cause the vehicle to have trouble starting.
- You have issues accelerating. If the exhaust pressure increases due to a clogged converter, you may have trouble accelerating your car.
- Failed emissions test. Finally, if your vehicle fails its emissions test, it could be a sign of a problem with the catalytic converter.
If you experience any of these issues, the smartest thing to do is take your car to the mechanic for inspection. Sometimes, you can
fix the catalytic converter without replacing it
. Other times, the damage is beyond repair, and you will need a replacement. MORE: How to pass emissions testing
How to find affordable car insurance
If your catalytic converter gets stolen, the last thing you want to do is pay for the replacement out of pocket. Make sure that your car insurance policy includes
comprehensive coverage
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Do all cars have catalytic converters?
Every car built after 1975 should have a catalytic converter.
How long does a catalytic converter last?
Catalytic converters are designed to last around 10 years or 100,000 miles. However, your driving habits and location can affect the lifespan of your catalytic converter.
Can a car run without a catalytic converter?
Cars can run without catalytic converters. However, driving a vehicle without one is illegal in all 50 states.
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