CITROËN C4 Handbook page 180

Driving
Particular situations
In certain situations (e.g. starting the engine),
the parking brake can automatically alter its
force. This is normal operation.
To advance your vehicle a few centimetres
without starting the engine, but with the ignition
on, press on the brake pedal and release the
parking brake by pulling then releasing the
control lever A. The full release of the parking
brake is confirmed by the warning lamps in
the control lever A and in the instrument panel
going off and display of the message "Parking
brake off".
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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 electronic stability control provides stability
during emergency braking.
If the emergency braking malfunctions,
the message "Parking brake faulty" will be
displayed.
In the event of failure of the electronic
stability control system, signalled by
the illumination of this warning lamp,
braking stability is then 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.