Audi A8 2019 Service Training page 60

Action of the 48 V battery in response to a crash signal
General
If Airbag Control Module J234 has detected a crash, the
48-volt battery is deactivated for safety reasons. In the
event of an accident, J234 sends a collision signal to the
data bus. The gateway (J533) relays this information to the
the 48V Battery Control Module A6 via the hybrid CAN bus.
This control module is located inside the housing of the
48-volt battery.
Response to a minor accident
As described above, J234 sends a crash signal to the data
bus in the event of a minor accident. The battery isolator
igniter receives this message and disconnects the 48-volt
battery. A 48-volt battery disconnected by a minor accident
can be reactivated by a terminal 15 ON/OFF switching
signal.
Response to a severe accident
In the event of a severe accident, the signal to isolate the
48-volt battery is transmitted in two different ways. This
provides redundant (multiple) backup for signal transmission.
› Pathway 1: The 48-volt battery is disconnected as
described under "Response to a minor accident".
› Pathway 2: J234 is also wired discretely to the 48V
Battery Control Module A6. In the event of a severe
accident, J234 energizes the battery control module via
the discrete wires by applying a current of approximately
1.75 to 2 A and instructs the battery isolation igniter to
disconnect the 48-volt battery. If a 48-volt battery is
disconnected by a severe accident, it can be reactivated
using Guided Fault Finding on the VAS Scan Tool.
Note
The 48-volt battery is not disconnected in the event of a rollover accident.
56
Battery Interrupt Igniter, 48 Volt N751 is mounted on its
printed circuit board. A6 instructs the battery isolation
igniter to disconnect the 48-volt battery. Contrary to what
the name might suggest, N751 does not have a pyrotechnic
charge. The igniter is a relay. The igniter is an integral part
of the 48-volt battery and cannot be replaced separately.
Battery Interrupt Igniter, 48 Volt N751
on the PCB of the 48V Battery Control Module A6
662_067