Volkswagen The Golf 2004 Service Training page 39

Trailer detection control unit J345
Fitting location
The trailer detection control unit can be found on
the left behind the luggage compartment trim in
the side panel.
Task
The trailer detection control unit has the task of
detecting whether a trailer is connected, it
controls the trailer lights and also checks the
function of the lights.
The bulb current of each bulb wiring circuit is
checked. There is an exception in the fog light
and tail lights, as these are not available on
every trailer.
Control of the trailer lighting is provided by the
onboard supply control unit, which
communicates with the trailer detection control
unit via the CAN data bus.
In the Golf 2004 there is no warning lamp in the
dash panel insert control unit J285 for trailer
detection.
Retrofitting of the trailer detection control unit is
possible. However, problems may arise due to
the fact that connection to the CAN data bus is
necessary.
Please refer to the electronic service
information system (ELSA) for the
latest pin/terminal assignment and
coding of the trailer detection control
unit.
Installation of aftermarket control units, which
have not been authorised by Volkswagen, is not
recommended. In most cases, these are
connected to the tail lights, which can result in
faulty operation of the bulb monitoring system.
In addition, the same tail light of the Golf 2004 is
actuated, depending on the function, in varying
degrees of brightness.
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