CITROEN DS4 Owner's Handbook Manual page 55

Deactivation indicator lamps
If one of the following indicator lamps comes on, this confirms that the corresponding system has been switched off intentionally.
This is may be accompanied by an audible signal and a message on the multifunction screen.
Warning lamp is on
Passenger's fixed in the instrument
airbag system panel and/or seat belt
and front passenger's
airbag warning lamps
display.
Cause
The control switch, located in the
glove box, is set to the OFF position.
The passenger's front airbag is
deactivated.
Action/Observations
Set the control to the "ON" position to activate
the passenger's front airbag.
In this case, do not fit a child seat in the rear-facing
position.
53
Monitoring