1° step: to verify that the car radio has on the lateral label acronym KML (kit main libre);

2° step: to verify that the diaplay has the indication of the external temperature on the angle to right and not to the center. In contrary case it will have to replace it with one adapted, for the C4 are difficult to reperire, but those for peugeot work, but the lighting system is red...

3° step: buy the bt unit and the relative connector, the microphone and a connector most/fakra for the connection with the rd4.

4° step: realize the wiring and the connections, 3 cables go to the bsi (12V + 2 MUX) and 4 cables to then rd4 (ground + audio dx + audio sx + audio ground).

5° step: go in citroen and codifying the bsi, the display and the line-in aux1 with the Proxia so that it comes seen and recognized the handsfree bt.

The End!