How can I create an xml for a peugeot 407 2008?
Creating a CAN description for the vehicle from the scratch is not an easy task, although possible.
Before tackling this head on, I would suggest using day or two trying to find CAN descriptions for your vehicle. Ask make/model enthusiast forums/social media, search beg and borrow.
First thing to do is to connect your vehicle CAN bus to see all CAN traffic on some software. RealDash has a built-in CAN monitor, but there are other professional desktop software to analyse CAN traffic in more detail.
Once you have solid connection and can see all the CAN data, then it is a matter of trying to interpret data. Start by trying to find bytes for relatively easy and slowly changing values like Coolant Temperature. If you know that your coolant temperature is say 90 degrees Celsius, try to find a byte that is close to 0x5A, or something with typical conversion range like C+40.
So its not easy and requires either experience or a LOT of stamina to get thru as there is a LOT of data running around in CAN bus on any vehicle.