What is a catalytic converter? Why these valuable parts are targets for theft.

Stolen catalytic converters recovered by detectives at a storage unit in Phoenix.

Cars making loud noises are never a good sign and are a particular hassle when the cause of the noise is a missing catalytic converter.

Catalytic converters are regularly targeted car parts, sometimes stolen right out of driveways. This month, three members of a California family pleaded guilty to their roles in a $600 million catalytic converter theft ring, USA TODAY previously reported.

The theft can cause car owners headaches and up to thousands of dollars. What are catalytic converters, and why are they stolen so often?

What are catalytic converters?

Catalytic converters are your car’s way of filtering out harmful engine exhaust pollutants. This exhaust system converts pollutants (hydrocarbons, carbon monoxide and nitrogen oxides) into compounds that already make up our atmosphere (nitrogen, oxygen, carbon dioxide and water).

Well-designed catalytic converters can reduce hydrocarbon and carbon monoxide emissions by about 90%, as well as Diesel Particulate Matter emissions by 25-35%. These converters work by using metallic catalysts to drive reactions at lower temperatures than would normally be needed.

Per guidelines from the Environmental Protection Agency, cars made in or after 1975 have catalytic converters to curb pollutants. According to the EPA, starting in 1988, anyone installing or selling a catalytic converter that hasn’t met federal guidelines may face penalties of up to $25,000 for each installation.

Some states have even adopted stricter environmental protections for catalytic converters. The California Air Resources Board requires CARB-compliant catalytic converters, which use an enhanced process to meet the stricter standards for curbing harmful emissions. California and Colorado require all cars to use CARB-compliant catalytic converters. The state of New York requires cars made in 1993, 1994, 1996 and newer to use the converters, and Maine mandates CARB-compliant catalytic converters for cars made in and after 2001.

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Why do people steal catalytic converters?

Reported catalytic converter thefts increased by 325% between 2019 and 2020. The reason for stolen converters is the explanation behind any theft — money. The rhodium, palladium and platinum used in these parts are valuable, and rhodium can go for $20,000 per ounce, according to the National Insurance Crime Bureau. Palladium costs nearly $3,000 per ounce, and platinum costs about $1,128 per ounce.

Twenty-six states proposed bills in 2021 to prevent catalytic converter theft, with 10 states passing legislation.

NICB recommends taking precautions to prevent your catalytic converter from getting stolen:

  • Install an anti-theft device.

  • Park trucks in a well-secured enclosed area.

  • Park personal vehicles in a garage or in a driveway with motion sensor security lights. Always lock your car.

  • Get your Vehicle Identification Number etched onto your car’s catalytic converter, which will help law enforcement track and identify the stolen parts. This can be done at a muffler shop or at a local NICB catalytic converter event.

Can you drive without a catalytic converter?

If your catalytic converter was stolen, you may get an engine error code from your vehicle. Because the converter muffles the exhaust sound, you also will notice a louder, unusual sound coming from the exhaust, TheMotorGuy.com reports.

While driving without a catalytic converter is technically possible, you may run into legal issues if you live in a state where emissions tests are required to use the vehicle. Federal law also prohibits the removal of catalytic converters.

How much does it cost to replace a catalytic converter?

Prices vary when it comes to replacement converters because of the fit of the part. Universal replacements can cost about $200-$300 according to AutoZone, but newer vehicles may require direct-fit converters because the original catalytic converters are incorporated into the exhaust manifold. These direct-fit converters can cost as much as $2,500.

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This article originally appeared on USA TODAY: What is a catalytic converter? Here's how to protect yours from theft.