Self-Study Program

27
Alternator warning lamp
The warning lamp indicates a fault in the alternator or a malfunction in the vehicle electrical system.
The alternator sends status messages to the energy management control unit J644 via the bit-synchronous
interface. These status messages are the basis for the activation of the warning lamp.
The information for activating the warning lamp is sent to the convenience CAN bus by the energy
management control unit J644 and relayed to the dash panel insert CAN bus via the data bus diagnostic
interface (gateway) J533. The control unit with display in dash panel insert J285 reads this information from
the dash panel insert CAN and activates the warning lamp.
The warning lamp is activated if any of the following faults occur:
– The engine is running and a mechanical fault is present in the alternator for at least 10 seconds.
– An electrical fault is present in the alternator or at the bit-synchronous interface for at least 10 seconds.
Both faults trigger entries into the energy management control unit J644.
The warning lamp is not activated:
– No communication between the energy
management control unit J644 and the control unit
with display in dash panel insert J285.
The alternator or the regulator in the alternator can
send 3 fault messages via the bit-synchronous
interface to the energy management control unit:
–Mechanical faults
– Electrical fault
– High-temperature fault
Note
Important! If the regulator is faulty, it is
possible that the alternator warning
lamp is not being activated. This is the
case if a fault in the regulator is
preventing information from being sent
to the bit-synchronous interface.
As a result, the energy management
control unit J644 does not receive any
information on the activation of the
warning lamp.
Control unit with display in
dash panel insert J285
Energy
management
control unit
J644
Alternator
364_059
Data bus
diagnostic
interface
J533
Dash panel insert CAN bus
Convenience
CAN bus