how can i fix my o2 plate citroen c5?

This is the service indicator, normally shows when ignition turned on and goes out when engine started. If it remains on this would indicate your car is due a service.
It can be turned off, if the same as a 2001 model, by holding the trip meter button in and then turning the ignition on, this will be followed by a count down number to zero.
Hope this helps.

Citroen Junkie
April 2013

u nd a service

tommy
August 2008