The catalytic converter, mounted in the exhaust system, is a muffler-shaped device designed to reduce tailpipe emissions. It contains a ceramic honeycomb shaped material coated with alumina and impregnated with catalytically active precious metals such as platinum, palladium and rhodium.
The catalyst's job is to reduce air pollutants by oxidizing hydrocarbons (HC) and carbon monoxide (CO). Catalysts containing palladium and rhodium also oxidize nitrous oxides (NOx).
On some trucks, the catalyst is also fed by the secondary air system, via a small supply tube in the side of the catalyst.
No maintenance is possible on the converter, other than keeping the heat shield clear of flammable debris, such as leaves and twigs.
Other than external damage, the only significant damage possible to a converter is through the use of leaded gasoline which will clog it, or through (excessive) heat-caused melting resulting from a too rich or too lean fuel/air mixture. Both of these problems will ruin the converter through contamination of the catalyst and will eventually plug the converter causing loss of power and engine performance.
When this occurs, the catalyst must be replaced. For catalyst replacement, see the exhaust system procedures in Engine & Engine Rebuilding .