Mercedes-Benz OM 471 Introduction Into Service Manual page 111

System components
Tasks
f Evaluating the positions of the EMERGENCY OFF switch (S30)
and the frame EMERGENCY OFF frame (S31)
f Disconnecting the on>board electrical system from the
battery, when the EMERGENCY OFF switch (S30) or the
frame EMERGENCY OFF switch (S31) is pressed
Design
f Control electronics
f Bistable relay for disconnecting the on>board electrical
system from the battery
Function
The battery disconnect switch (BESO) control unit (A33) evaluates
the positions of the EMERGENCY OFF switch (S30) and the frame
EMERGENCY OFF switch (S31) via the input signal.
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i As a redundant message on the exterior CAN (CAN 1), the
battery disconnect switch (BESO) control unit (A33) also transmits
a pulse width modulated signal (PWM signal) via a direct line to
the sensor and actuator module, cab (SCA) control unit (A7). If the
battery disconnect switch (BESO) control unit (A33) recognizes
that the EMERGENCY OFF switch (S30) or the frame EMERGENCY
OFF switch (S31) was pressed, it changes the duty cycle of the
PWM signal from 50% to 75%, whereupon the sensor and
actuator module, cab (SCA) control unit (A7) recognizes that the
on>board electrical system starts being disconnected.
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– This printout will not be recorded by the update service. Status: 09 / 2011 –
When the EMERGENCY OFF switch (S30) or the frame
EMERGENCY OFF switch (S31) are pressed, the battery disconnect
switch (BESO) control unit (A33) disconnects the on>board
electrical system from the battery. Even before the on>board
electrical system is disconnected from the battery, it sends a
message to the exterior CAN (CAN 1) for further processing,
announcing that the on>board electrical system will be
disconnected from the battery. Among other things, the engine
management (MCM) control unit (A4) initiates the switching>off
of the engine due to this message. The on>board electrical system
is disconnected by a bistable relay integrated into the battery
disconnect switch (BESO) control unit (A33). The bistable relay is
actuated 800 ms after the battery disconnect switch (BESO)
control unit (A33) has recognized that the EMERGENCY OFF
switch (S30) or the frame EMERGENCY OFF switch (S31) was
pressed. The tachograph (TCO) (P1) continues to be supplied with
voltage by the battery disconnect switch (BESO) control unit (A33)
via a separate pin.
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