The short answer
Update all firmware, configure as one system, replace RJ45 cables with factory ones and check the DC fuse.
Plain explanation
From the Victron manual for the MultiPlus / Quattro system: Update all FW. Config as one system. The rest of the checklist is below; work through it in order. Installer only: DC and AC work on a live PV system is dangerous, so owners should note the code and call their installer.
Steps from the source
- Update all FW
- Config as one system
- Check cables/RJ45, replace with factory cables
- Check DC fuse
Source
Victron VE.Bus error codes (official docs), Err 3 / Err 17www.victronenergy.com ↗
Where installers ask this
General guidance based on the manufacturer's manual or the named source. Always follow the current manual for your exact model and your national code. DC and AC electrical work is for qualified installers only. Not affiliated with or endorsed by any brand named; trademarks belong to their owners.