Mercedes-Benz OM 471 Introduction Into Service Manual page 129

System components
Design
2 Electrical connection
A70 Exhaust aftertreatment unit inlet NOx sensor control unit
A70 b1 Exhaust aftertreatment unit inlet NOx sensor
The exhaust aftertreatment unit inlet NOx sensor control unit
(A70) and the exhaust aftertreatment unit inlet NOx sensor (A70
b1) are interconnected via an electrical line that cannot be
disconnected, and form a single unit.
The exhaust aftertreatment unit inlet NOx sensor
(A70 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.
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The exhaust aftertreatment unit inlet NOx sensor (A70 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 inlet
NOx sensor (A70 b1) and the exhaust aftertreatment unit inlet
NOx sensor control unit (A70) has a defined length of approx.
60 mm.
W14.40>1587>12