Code U1031?

Hello, U codes have to do with communication between modules on the vehicles data network. Service information does not specify exactly which module (computer) in the vehicle is having the issue communicating, this vehicle actually has multiple data networks that run at different speeds. But the issue here can be either a short circuit in the data network, it can be a faulty module sending out bad data packets, it's impossible to tell what exactly is wrong with the vehicle without being at it to diagnose what might be happening. There are many modules built into the vehicle, so it will need to go into a shop to determine where the fault is. Unfortunately, this isn't as easy as checking a fuse. The data networks in modern vehicles are very complex, and I use an oscilloscope to check network activity and see what the voltage levels are, as well as a high-end scan tool to try to determine which modules are sending data on the network and which ones are not. I'll post a couple diagrams showing the entire communications network just to give you an idea of how many modules there are on it.

Diagrams 1 and 2 go together and 3 and 4 go together top and bottom. On the first diagram highlighted in yellow is the 16pin connector where a scan tool is hooked up, but you can see that every blue box is a computer module in the vehicle.
Also on diagram 1 at the top is the Totally Integrated Power Module (TIPM), there you can see all the different data networks and their speeds. The reason the vehicle is not running well is because there is a disruption in the network and the correct information is not being sent between modules. I'm sorry I can't be more help than this, the TIPMs are known failure points, but this needs to be diagnosed correctly and not just have parts replaced and hope it gets fixed. That would get very expensive very quickly.

https://www.2carpros.com/articles/can-scan-controller-area-network-easy