It is not a known fault the very first C1's used to stop showing the speed on the speedo because the Engine Ecu was being back spiked by the ABS Block though, hubby is a Citroen tech, but unfortunately having a mass produced ECU rogue ones turn up and spoil the enjoyment of owning a vehicle, I hope it gets sorted for you and doesn't spoil the pleasure of owning a C1, I have one and love mine