mine is a 52 plate 2.0 hdi, apparently 2002 was the changeover year so is a bit hit n miss if any particular obd reader would work on it. i found a cheap autel autolink al301 on the halfords site for £29.99 so had a drive over to ask them if it would work. they dont have them in stock, they are online only but the bloke said that he tried it on a 51 plate pug hdi and it worked. i decided to take a chance and buy one and it did work on mine.
i would imagine yours being 2003 it should work on yours too if it has a port like https://citroenc3own...se-board-loc/30
the link for the reader is http://www.halfords....obd-code-reader