Catalytic Converter: Description and Operation

Converter Types:

PRECAUTIONS
CAUTION: Prolonged operation with a misfiring or flooded engine may cause the converter to overheat. This could cause damage either to the catalyst itself or the operating vehicle and possible personal injury.

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.


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 allows for a faster chemical reaction to take place and although it enters into the chemical reaction, it remains unchanged, ready to repeat the process.
This device sometimes requires the use of heat shields, due to its high operating temperatures. The heat shields are necessary to protect chassis components, passenger compartment, and other areas from heat related damage.

General Motors uses four different converter designs in conjunction with two types of catalysts.
The four converter designs are:

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

The two types of catalysts used are an Oxidation catalyst and a Three-Way (Oxidation/Reduction) catalyst. The Oxidation catalyst is coated with a material containing platinum and palladium which lowers levels of carbon monoxide and hydrocarbons. The Three-Way (Oxidation/Reduction) catalyst is coated with platinum and rhodium which lowers levels of oxides of nitrogen (NOx), as well as carbon monoxide and hydrocarbons.
All dual bed converters, whether monolith or pellet type, contain both oxidation and three-way catalysts.

A small diameter fuel tank filler neck is used on catalytic converter equipped vehicles to prevent the use of leaded fuel pump nozzles.
Since the use of leaded fuels, or fuel additives containing lead, contaminates (damages) the catalysts, the use of unleaded fuels is mandatory on catalytic converter equipped vehicles.