[bishopts]

There are several independent can busses. Any idea what codes?

Usually you're gonna have a pretty standard U1000 code but you can get sub code number that will indicate which can bus is not communicating.
If you have no place to start then try things related to your first thought. Things that get wet.
Steering rack connector, trunk flooding and drowning the fuel pump control module, water intruding the electric parking brake module, eLSD module case broken open from a rock.

Out if 100 techs probably 3 could tell you how a can bus actually works. Out of 500 techs probably less than 10 can actually diagnose can bus faults.

Our cars are kind of a mesh bus layout. Things like the pcm will not have a dedicated connection to the data link connector, it will be more like the DLC goes into the power steering contol module, then leaves from there in the same bus but in different wires to the ABS module. Then leaves that to the PCM. But also a whole different bus will go from the PCM to a common bus controller in a mostly star setup.
So you need to see the topology of the communication network as a whole, then look at all of the modules codes to help narrow down where to start. If all of the modules say lost communication to PSCM then it would be a good idea to inspect the rack for damage to the connectors and housing.