CITROËN DS4 Owner's Handbook Manual page 278

Towing a trailer, a caravan, etc.
Towbar suitable for the attachment of a
trailer or caravan with additional lighting and
signalling.
Your vehicle is primarily designed for
transporting people and luggage, but it may
also be used for towing a trailer.
We recommend the use of genuine
CITROËN towbars and their harnesses
that have been tested and approved
from the design stage of your vehicle,
and that the fitting of the towbar is
entrusted to a CITROËN dealer or a
qualified workshop.
If the towbar is not fitted by a CITROËN
dealer, it is imperative that it is
fitted in accordance with the vehicle
manufacturer's instructions.
Driving with a trailer places greater demands
on the towing vehicle and the driver must take
particular care.