Mercedes-Benz OM 471 Introduction Into Service Manual page 116

Design
2 Electrical connection
A57 Exhaust aftertreatment unit outlet NOx sensor control
unit
A57 b1 Exhaust aftertreatment unit outlet NOx sensor
The exhaust aftertreatment unit outlet NOx sensor control unit
(A57) and the exhaust aftertreatment unit outlet NOx sensor (A57
b1) are interconnected via an electrical line that cannot be
disconnected, and form a single unit.
The exhaust aftertreatment unit outlet NOx sensor
(A57 b1) has a similar design to a wide>band oxygen sensor. It is
fitted with its basic elements such as the so>called Nernst cell and
the oxygen pump cell.
Its front part in the measuring probe which projects out into the
exhaust consists of a metal housing with openings and a gas>
permeable ceramic body inside made out of zirconium dioxide.
The surfaces of the ceramic body are fitted on both sides with
electrodes made out of a thin platinum layer. The measuring
probe is in contact with outside air via a reference air duct.
The metal housing protects the ceramic body inside against
mechanical stress and sudden increases in temperature.
i Introduction of engine OM 471 and exhaust aftertreatment > 09/2011 >
– This printout will not be recorded by the update service. Status: 09 / 2011 –
System components
The exhaust aftertreatment unit outlet NOx sensor (A57 b1) is
fitted with an integral heating element which serves to rapidly
achieve the operating temperature of about 800 ∞C that is
required for the chemical processes taking place therein.
The electrical line between the exhaust aftertreatment unit outlet
NOx sensor (A57 b1) and the exhaust aftertreatment unit outlet
NOx sensor control unit (A57) has a defined length of approx.
60 mm.
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