Problem with the Can Fiat Siena 2005 system

Hi everyone, I'm new to the site and the forum. I'm a mechanic, and I'm having a problem with the CAN system on a 2005 Fiat Siena with a Bosch Motronic ME 7.96F fuel injection system.
The CODE light is on in the dashboard. I used a scanner, and it says there's a communication problem with the CAN system. Has anyone else experienced this? I have a lot of technical information, but I can't find anything to tell me what each wire carries—power, ground, or signal. I hope I can find some guidance, haha.