CITROËN DS5 Owner's Handbook Manual page 112

Emergency braking
In the event of a failure of the main service
brake or in an exceptional situation (e.g. driver
taken ill, under instruction, etc) a continuous
pull on the control lever A will stop the vehicle.
The Dynamic Stability Control system provides
stability during emergency braking.
If the emergency braking malfunctions, the
message "Parking brake control faulty" will be
displayed.
If a failure of the DSC system is
signalled by the illumination of this
warning lamp, then braking stability is
not guaranteed.
In this event, stability must be assured by the
driver by repeating alternate "pull-release"
actions on the control lever A .
The emergency braking must only be
used in exceptional circumstances.