Only the early dashboard warning lights (2002 to 2006) are shown here, but the full C3 dashboard display is shown and explained in this topic for Citroen C3 Dashboard Display.
Later models, like the 2006 to 2009 C3 have their warning lights described in this topic - Citroen C3 dashboard warning lights 2006 to 2009
and the much later models like the 2009 to 2013 C3 have the dashboard warning lights description in this topic - Citroen C3 dashboard warning lights (2011) A51
2002 to 2006 C3 models have these dashboard warning lights:
Left hand direction indicator
Right hand direction indicator (both left and right indicate Hazard lighting is active).
Sidelamps on.
Main beams active.
Front foglamps active.
Rear Foglamps active.
Drivers seat belt not buckled comes on for 5 second when the engine is started as a reminder to wear the seatbelt or comes on if the drivers seat belt is not fastened.
Airbag warning lamp
Front passengers airbag deactivation warning lamp
Engine Auto-diagnois if it flashes or lights while the engine is running it indicates a fault within the fuel injection, ignition or anti-pollution systems. 'Consult Citroen dealer as soon as possible.' Or plug in one of these
to the diagnostic port to do the diag yourself 
Battery charge Should not be lit when the engine is running. If it lights permanently, contact a Citroen dealer.
Engine oil pressure If it lights while you are driving, stop the engine, check the level. If it remains lit despite the level being correct, contact a Citroen dealer.
Dashboard warning lamp for hand-brake, brake fluid level and braking distribution fault With the engine running, the lighting of this warning lamp indicates that the parking brake is on or not properly released, that the brake fluid level is low or that the braking system is malfunctioning. If the warning lamp remains on even after you have released the parking brake, stop immediately (if you can) and contact a CITROËN dealer.
ESP warning lamp - in operation If the ESP is active, the ESP warning lamp flashes on the dashboard.
In the event of a problem If the vehicle is moving, the lighting of the ESP warning lamp on the dashboard, accompanied by an audible signal (beep), indicates a malfunctioning system. Have the system checked.
Diesel Pre-heater is active.
Anti-lock Braking System The ABS warning lamp lights up when you switch on the ignition: it should go out after a few seconds. If it does not go out, there could be a system malfunction.
Fuel Gauge Presence of water in the diesel is indicated by all segments of the display fuel level flashing.
Coolant temperature alert dashboard warning Permanent lighting of all the luminous bars of the coolant temperature gauge accompanied by an audible signal (beep) indicates an abnormally high engine coolant temperature.
