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When retrofitting a trailer socket, the socket must no longer simply be connected to the rear lights.
In this case, the onboard supply control unit is no longer able to carry out functions such as bulb diagnosis
via the defined bulb load or dimmed light actuation, because it is unable to distinguish between the
vehicle's lights and a possible short-circuit in the relevant power circuit.
However, the trailer detector control unit also feeds
messages into the CAN data bus, so that the affected
control units can switch to trailer mode.
This information is required:
- At the onboard supply system control unit to
actuate the rear fog light. This is switched off
during trailer operation to reduce the dazzle effect
to which the driver is exposed.
- At the ABS and ESP control unit to adapt the brake
system control functions to trailer operation.
- At the parking aid control unit to deactivate the
sensors for the rear sensing range.
- At the anti-theft alarm system to integrate the
trailer into monitoring when the trailer line is
connected. Since the microswitch in the trailer
socket has been omitted, this is carried out via bulb
sensing.
A trailer with LEDs in its turn signals and rear lights cannot be detected, because its power consumption is
less than 5W. During trailer simulation, workshops must ensure that their test boxes provide this output
value of 5W as consumers.
S338_115
Trailer detector
control unit J345
Trailer socket
Onboard supply
control unit J519
CAN data bus
Voltage supply
Rotary switch for lighting
Tail lights on the trailer
