How a Catalytic Converter Works

This article has information about how an automotive catalytic converter works.

Experiments determined that passing exhaust gases over a catalyst will cause the pollutants in the exhaust to be completely burned and result in water (H2O) and carbon dioxide (CO2) byproduct. The catalytic converter was developed in the early 1970's when severe air pollution was prevalent, and was made mandatory in automobile manufacturing in the US in 1976. The catalytic converter or "cat" is an emission control device designed to remove unburnt fuel in the exhaust system.

This unburnt fuel is a major component in air pollution. The name catalytic converter was derived from its operation, utilizing a catalyst combined with heat to convert the unburned gases into burned gases. The catalyst is heated to excite the chemical catalyst, this burns the unburned fuel making the catalyst even hotter furthering the effect (thermo reaction.) A catalytic converter starts with a ceramic honeycomb about 3 inches by 5 inches by 8 inches which can vary. This honeycomb is coated with a thin layer of catalyst material and is placed inside a metal container with an inlet and outlet connection. The honeycomb design provides maximum exposure to the exhaust gases.

Vehicle Underside
Catalytic Converter Location

Catalytic converter locations can vary depending on manufacturer. Some vehicles require multiple units to clean the exhaust gases more thoroughly. When the catalyst breaks apart it can clog the outlet of the catalytic converter causing the exhaust to backup into the engine forcing low power or stalling. Visit - Plugged catalytic converter

In order for the converter to operate properly it must operate at a high temperature. When a vehicle's engine is cool air is pumped into the exhaust system to super heat the catalytic converter to aid in this heating process.

An oxygen sensor delivers feedback information which the PCM (computer) uses to determine the amount of fuel injected into the engine. When this system malfunctions it can cause the cat to overheat and break apart. Visit - Oxygen sensor testing.

When a converter fails replacement is necessary. Visit - Catalytic converter replacement.

Common Problems

  • The catalyst in the catalytic converter can break apart causing low power and stalling.
  • The catalytic converter can get very hot causing a fire hazard when vehicle is parked over dry brush.


This guide knowledge base was created by the 2CarPros Team, and by Ken Lavacot: Automobile repair shop owner and certified master automobile technician of over 30 years. If you have question or need help please ask one of our experts we are happy to help. Please visit our 2CarPros YouTube Channel.

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