Get the fault code read to establish the fault. This will cost between 30 and 50 pounds at a garage and they will reset it too. The trouble is this will not cure the underlying snag that caused the warning. In order to do this you must replace/repair the faulty component as indicated by the reader. Cheap readers can be bought online and can save you lots of money if you are constantly resetting the light whilst fault finding. Its a Citroen so good luck; you'll need it.
old biker
January 2017