On-Board Diagnosis System II - Volkswagen Technical Site

System Components (Gasoline Engine)
The catalytic converter
The catalytic converter is the key component for
emission control. Whereas development began
with the open-loop system, today a closed-loop
system regulated exclusively by lambda probes is
used in the motor vehicle industry.
A catalytic converter in the chemical sense is a
substance which promotes, accelerates or makes
possible a chemical reaction.
The substance itself - in this case, precious metals
such as platinum, rhodium and/or palladium are
used - does not take part in the reaction and is
not used up.
For reasons of effectiveness, it is important for
the surface of catalytic converter to be as large
as possible. Therefore, the precious metal is
applied to a ceramic or metallic substrate
bearing numerous longitudinal channels. The
surface area was again enlarged by means of a
so-called wash coat. This is what makes highly
efficient exhaust gas treatment possible.
Lambda probe I
(primary catalytic
converter probe)
Lambda probe II
(secondary catalytic
converter probe)
175_037
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