I can't give you a true answer for what the fault code is but I can say I wouldn't expect it to be coil pack related.
OBD codes are a standardised fault code form across all manufacturers.
Codes can start with various letters. if it was engine related I'd expect it to start with P - the standardised character for power train.
You have a code that begins with B - which I believe relates to Body and a U code, which is a User Network code.
Essentially I'd guess it's some sort of issue detected over the CANBUS network, where the U code is telling you that there is a communication error on the CANBUS network.
The first number of the code tells you whether it's a generic fault code - common across all cars / all manufacturers or whether it's a manufacturer specific code.
0 = generic code. 1 = manufacturer code.
So in your case you have two Fiat specific fault codes.
If Eklipze is correct I'd recommend checking the plugs on the back of the rear light clusters and inspecting the earth connectors.
It's not unheard of for the plug to get melted and the earth connection compromised as a result - which could be the root of your issues. You'll see the connections on the earth pin / plug blackened and burnt. I soldered an additional earth to my rear light cluster when it did this!
