Catalytic Converter: Description and Operation

Converter Types:

SYSTEM DESCRIPTION
The catalytic converter is an emission control device added to the exhaust system to effectively reduce the levels of carbon monoxide, hydrocarbons, and in some cases oxides of nitrogen, exiting the tailpipe. The converter contains catalysts that promote oxidation of residual hydrocarbons and carbon monoxide gases in the exhaust.

More recently, converters contain an additional catalyst (rhodium) that also promotes reduction of oxides of nitrogen emissions. These type converters are referred to as "Three-Way Catalytic converters. Three-Way converters reduce these harmful compounds into their constituent elements oxygen and nitrogen gas.

Because of the high temperatures generated within the converter, heat shields are necessary to protect chassis components, passenger compartment, and other areas from heat related damage.

CAUTION: Prolonged operation with a misfiring or flooded engine may cause the converter to overheat. This could result in damage to the catalyst or the vehicle, and possible personal injury.

CONVERTER TYPES
General Motors uses four different converter designs in conjunction with the two types of catalysts, an oxidation catalyst and a Three-Way (Oxidation/Reduction) catalyst. All dual bed converters, whether monolith or pellet type, are three-way converters containing both oxidation and reduction catalysts. The four converter designs are:

1. Single bed monolith
2. Dual bed monolith
3. Single bed pellet
4. Dual bed pellet

The monolith type converters consist of a porous ceramic "honeycomb" substrate impregnated with the catalytic elements. The pellet type is filled with porous ceramic pellets impregnated with the catalysts.

NOTE: The use of leaded fuels, or fuel additives containing lead, plugs the pores in the substrate material containing the catalysts, rendering the catalyst ineffective. Only unleaded fuels should be used in catalytic converter equipped vehicles. A small diameter fuel tank filler neck restrictor is used on these vehicles to prevent the introduction of leaded fuel from the larger diameter leaded fuel pump nozzles.

NOTE: When jacking or lifting vehicle from frame side rails, be certain lift pads do not contact catalytic converter otherwise damage to converter may result.