I have one ELm327 interface but working only for ECU
Interface for body computer?? vag or kkl or what to buy??

Please help me!

You've not said what software it is you're using - which is just as likely to be the issue as the cable.

An ELM interface will deal with most ECUs on the car although adapter cables are needed for some.

Check out the MultiECUScan website. This is the software you should be using for your Fiat, if you're not already. The website has a supported vehicles list and gives you a breakdown of what ECUs on the car are supported and what you need to connect to those ECUs.

I can use Multiecuscan with my PC, but what cable to connect BC?
Thanks for your reply

Have a look at ebay and search for multiecuscan. You will see cables which have adaptors to connect to all parts of the car.

Again, refer to the MultiECUScan website for what cables you can use / need to connect to certain elements of the system.

You can use an ELM cable to connect to the body computer.

Note that some cheap chinese cables do not function correctly in order to get access to all the modules. If you look on eBay and search for MultiECUScan there are sellers on there that will sell ELM cables that are correctly setup and modified to work with the latest versions of MultiECUScan.