Citroen C3 1.4 Petrol - Vahe
My wife's C3 has suddenly developed an electrical fault. The instrument lights were permanently on (even after locking the car) the speedometer would not work, the fuel gauge showed empty and had only done 90 miles on a full tank. The radio has gone haywire, indicators would not work, odometer would not work, air bag light and headlight indicator on. I disconnected the battery and waited a few minutes to allow the computer to reset. Connected the battery back up and it seems to have cured the problem. Will see how it goes but if anyone has an idea as to what the fault is, I shall be grateful for a reply.
Citroen C3 1.4 Petrol - LeePower
Sounds like the BSI software has had a major sulk, Disconnecting the battery re boots the system.

How old is the car?

Should still be under warranty, Citroen dealer, both keys & security card & let them look at it, Most likely update the software for you FOC.

Citroen C3 1.4 Petrol - Aprilia
I heard of this before on Cits. Maybe there should be a big 'RESET' button on the dash?
Citroen C3 1.4 Petrol - LeePower
The instrument lights being permanently on is a big clue, That's a warning that something isnt right with the CAN system.

On Peugeot / Citroen stuff that is multiplexed like this C4.

Something disconnected / missing / faulty on the CAN system will then light the whole dash up as a warning, Trip to the dealer for this one.