Underbody Catalyst

Description and Operation 1-63

Catalyst And Exhaust Systems

Underbody Catalyst

The underbody catalyst is located after the light off catalyst. The underbody catalyst may be in line with the light off catalyst, or the underbody catalyst may be common to 2 light off catalysts, forming a Y pipe configuration. For an exact configuration of the catalyst and exhaust system for a specific vehicle, refer to the Workshop Manual Section 309-00, Exhaust System for the exhaust system exploded view.

Three Way Catalytic (TWC) Converter

The TWC converter contains either platinum (Pt) and rhodium (Rh) or palladium (Pd) and rhodium (Rh). The TWC converter catalyzes the oxidation reactions of unburned HCs and CO and the reduction reaction of NO . The 3 way conversion can be best accomplished by always

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operating the engine air fuel ratio at or close to stoichiometry.

Exhaust Manifold Runners

The exhaust manifold runners collect exhaust gases from engine cylinders. The number of exhaust manifolds and exhaust manifold runners depends on the engine configuration and number of cylinders.

Exhaust Pipes

Exhaust pipes are usually treated during manufacturing with an anti corrosive coating agent to increase the life of the product. The pipes serve as guides for the flow of exhaust gases from the engine exhaust manifold through the catalytic converter and the muffler.

Heated Oxygen Sensor (HO2S)

The HO2S provides the PCM with information related to the oxygen content of the exhaust gas. For additional information on the HO2S, refer to Engine Control Components in this section.

Muffler

Mufflers are usually treated during manufacturing with an anti corrosive coating agent to increase the life of the product. The muffler reduces the level of noise produced by the engine, and also reduces the noise produced by exhaust gases as they travel from the catalytic converter to the atmosphere.

2016 Powertrain Control/Emissions Diagnosis, Gasoline Engines, 3/2015