To quickly check if it's not a broken wire in the CAN BUS, you could measure the resistance between pins 11 and 4 on connector C4 of the ECU (I might be wrong on the connector number, but you can check it in the service manual). With the car off, key out of the ignition, it should read roughly 60 ohms. If it reads 120 ohms, you probably have a CAN BUS wiring problem. Hopefully, it's just as simple as a bad RCM.
Good Luck,
-Jerry

PS. sometimes with a CAN BUS error, it will throw codes saying that it can't communicate with the HVAC module.