Eatu Output Nox Sensor, Component Description - Mercedes-Benz OM 471 Introduction Into Service Manual

System components
GF49.20>W>3009HA
ENGINES 471.9 in MODEL 963, 964 with CODE (M5Y) Engine version Euro V
ENGINES 471.9 in MODEL 963, 964 with CODE (M5R) Engine version EEV
Location
1 Exhaust aftertreatment unit
A57 EATU output NOx sensor control
unit
A57 b1 EATU output NOx sensor
The EATU output NOx sensor (A57 b1) is
screwed into the inlet tube of the exhaust
aftertreatment unit (1) from the outside
and forms one unit together with the EATU
output NOx sensor control unit (A57).
Task
The EATU output NOx sensor (A57 b1)
represents the actual measurement sensor,
whereas the EATU output NOx sensor
electronic control unit (A57) is used to
compute the NOx raw concentration in the
exhaust before exhaust aftertreatment by
the SCR catalytic converter and ammonia
slip catalytic converter.
Design
2 Electrical connection
A57 EATU output NOx sensor control unit
A57 b1 EATU output NOx sensor
The EATU output NOx sensor control unit (A57) and the EATU
output NOx sensor (A57 b1) are connected to each other via a non>
separable electrical line and form one unit.
The EATU output NOx sensor (A57 b1) is similar in 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.
The EATU output NOx sensor (A57 b1) is fitted with an integral
heating element which serves to rapidly achieve the required
operating temperature of about 800 ∞C for the chemical processes
taking place therein.
The electrical line between the EATU output NOx sensor (A57 b1)
and the EATU output NOx sensor control unit (A57) has a defined
length of approx. 60 mm.
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EATU output NOx sensor, component description

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