Started trouble shooting the CAN Bus, since the LRUs were not communicating.
Tried configuring the G3X I/O protocols, but only got the communication with the GTX 45R transponder working, as it is not connected to the CAN Bus.
Checked the resistance between CAN Hi and CAN Lo, and found it to be the proper 60 ohms.
Talked to Garmin G3X Tech support at lunch time. They suggested making up a short CAN Bus cable and connecting it between PFD-1 and GSU 25 ADHRS to see if they would communicate.
I put together the recommended simple 2 point CAN Bus, removed the CAN Bus pins from the PFD-1 and GSU 25 connectors and replaced them with the pins from the simple 2 point Bus. Also inserted a jumper to make the PFD-1 a CAN terminator. Powered up the system and communication occured between these 2 LRUs with zero errors, so the problem is in the CAN Bus.
