Catalytic Converter
An emissions control device in the exhaust system that converts toxic gases into less harmful emissions through chemical catalysis.
The catalytic converter is an exhaust emissions control device that converts toxic byproducts of combustion into less harmful substances before they exit the tailpipe. It is a critical component for meeting federal and state emissions standards and has been required on all gasoline-powered vehicles sold in the United States since 1975.
Inside the catalytic converter is a ceramic or metallic honeycomb structure coated with precious metals — typically platinum, palladium, and rhodium. These metals act as catalysts, facilitating chemical reactions without being consumed. A three-way catalytic converter performs three simultaneous reactions: converting carbon monoxide (CO) to carbon dioxide (CO₂), converting hydrocarbons (HC) to carbon dioxide and water, and converting nitrogen oxides (NOx) to nitrogen and oxygen.
Catalytic converters can fail due to contamination (from leaded fuel, coolant leaks, or excessive oil burning), overheating (often caused by engine misfires sending unburned fuel into the exhaust), or physical damage. Symptoms of a failing converter include a sulfur or rotten-egg smell, reduced engine performance, poor fuel economy, and a check engine light with P0420 or P0430 diagnostic codes.
Due to the high value of the precious metals they contain, catalytic converter theft has become a significant problem. Replacement costs can range from $1,000 to $3,000 or more. Many jurisdictions now have laws requiring documentation when selling used converters.