Catalytic Converter — How It Works

The catalytic converter is a ceramic honeycomb structure coated with precious metals — platinum, palladium, and rhodium. These metals act as catalysts — they cause chemical reactions to occur at lower temperatures than would normally be required without being consumed themselves. Exhaust gases flow through thousands of tiny passages in the honeycomb and the chemical reactions convert harmful gases to less harmful ones.

Oxidation — converts carbon monoxide and hydrocarbons into carbon dioxide and water by adding oxygen. Reduction — converts oxides of nitrogen into nitrogen and oxygen by removing oxygen. These reactions happen simultaneously in a three-way converter — hence the name. The converter must be at operating temperature — above 500 degrees — for these reactions to occur efficiently.

Misfires — unburned fuel enters the converter and ignites inside it. The temperature can exceed 1,800 degrees and melt the ceramic substrate. This is why misfire codes are serious — they are not just about a rough-running engine. They are about protecting a component that costs $500 to $2,000 or more. Coolant contamination from a head gasket leak coats the catalyst surfaces and poisons them permanently. Oil burning coats the catalyst with phosphorus from the oil additives. A converter that has been physically damaged — from road impact or extreme heat — may have a collapsed substrate that blocks exhaust flow.