Here is what I have learned through the process of trying to get this figured out. After taking the boat to dealer, apparently the original Helmmaster system does not retain any error codes in the computer so they could not diagnose any problems. If you have this issue while driving boat, photograph any messages you get on your smart display so you can provide information to your tech. My dealer has Yamaha master technicians and not even they can work on the system at all because Yamaha bought this system from Volvo and only Yamaha factory techs have the tools to do any work on the system. You have to insist that the dealer schedule a Yamaha factory tech come and perform any upgrades to the firmware available, because the dealer cannot do this. Yamaha will not schedule their factory tech over phone, it has to be the dealer who contacts them. When the factory tech’s knowledge run out they have to call Volvo in Europe to get further assistance. The dealer’s YDS computer cannot work on the original Helmmaster system. This is a problem Yamaha needs to correct badly. They need to make information about this system public.
In my case, the issue appears to have been voltage related and after replacing batteries, fixing battery charger (blown fuse on battery lead from charger), and making sure batteries are fully charged, I have not had a recurrence. Fingers crossed! Because entering the pass by my home port during tidal swings can be challenging with fully functioning steering, let alone have a trip at wrong time.
I did pull connectors and clean contacts with CRC and then applied thin coat of dielectric grease to pins and seals before reseating for good measure. Be sure to use plastic safe contact cleaner. You also want to be sure battery lead to SCU is tight, corrosion free, on both ends. The battery lead is distinguished by being the much more flexible cable to the battery, it may have a label on it as well indicating SCU.
Yamaha did publish a Troubleshooting Guide for Helmmaster that appears out of print. If anyone has it, I would really like to read it. I have read the rigging guides, traced all wiring from helm to stern, and checked all connections. I could not find fault in the wiring itself.