CITROEN DS3 Handbook page 28

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 in the multifunction screen.
Warning/indicator lamp
Passenger's
airbag system
is on Cause
fixed. The control, located in the glove box,
is set to the OFF position.
The passenger's front airbag is
deactivated.
You can install a rearward facing
child seat, unless there is a fault with
the operation of the airbags (Airbag
warning lamp on).
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 rearward
facing position.