Three-Way Catalytic Converter (COC/TWC)

This is a dual catalytic converter consisting of two converters in one shell, with a mixing chamber between the two. Each converter is composed of a ceramic "honeycomb" coated with catalyst material.

The front, or "three-way catalyst" (TWC) converter acts on exhaust gases as they arrive from the engine. As gases flow from the TWC converter to the rear, or "conventional oxidation catalyst" (COC) converter, they mix with air from the thermactor pump injected into the mixing chamber. This air is required for proper oxidation of HC and CO in the COC converter.