We have a 1997 Hymer with 2.5TDI engine and were supplied with a red "master" key and also a Code Card. The dealer needed the red key back to do some work on the engine when carrying out a service.
Try googling "Fiat Code System Ducato" or have a look at http://www.motorhomefacts.com/forum-printtopic-1-83045-0-0-asc-viewresult-1.html.
Best of luck,
Brian, April 2010
