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[StableofZeros]

Title, my bms seems to be taking a dumper. Intermittent 12v system functionality, but still runs and drives.

[Curt]

The BMS is part of the battery. I think you're seeing a problem in the DC-DC converter, or in a connection to the DC-DC converter or 12V system, or to the MBB (main bike board) which controls the ENABLE signal of the DC-DC converter.

[StableofZeros]

Damn. Thanks for pointing that out, not sure what I was thinking. Not to turn this into a support thread, but is the sevcon related at all? The logs seem to be showing possibly multiple issues at once.

01/26/2025 15:48:41   SEVCON CAN EMCY Frame      Error Code: 0x1000, Error Reg: 0x01 Sevcon Error Code: 0x4884, Data: 0x00 0x00 0x00 0x58 0x02 , Sequence Fault
 07048   
Then later:
07063     01/26/2025 15:49:23   Calex 720W Charger 0 Connected   
 07064     01/26/2025 15:49:23   Calex 1200W Charger 1 Connected   
 Then:
07647     04/23/2025 06:30:29   ERROR: Cannot Connect Module 00! modv=109925mV, maxv=109925mV, minv=109925mV, raw0:109902mV, raw1:0mV, cur0:0A, cur1:0A, diff_allowed: 1727mV   
 07648     04/23/2025 06:30:29   DEBUG: Module 00 Contactor is now Open   
 07649     04/23/2025 06:30:29   Module 00                  vmod: 109.902V, batt curr: 0A
 07650     04/23/2025 06:30:29   BMS0 retry count is now 1   
 07651     04/23/2025 06:30:30   Module 00                  vmod: 109.932 maxsys: 109.932 minsys: 109.932 diff: 0.000 vcap: 107.687 prechg: 97%
 07652     04/23/2025 06:30:30   DEBUG: Module 00 Contactor is now Closed   
 

[Curt]

In my experience, it's normal for the logs to show a lot of deceptively negative sounding messages when nothing is wrong. And I don't think there is any computerized monitoring of the 12V system that they could use to generate logs regarding it.

The schematics for the 2016 FX are in this thread:
https://electricmotorcycleforum.com/boards/index.php?topic=7547.0
Probably the 2019 wiring hasn't changed too much from that.

See the DC-DC converter? All the 12V comes from there, passes through fuses and goes to electronics around the bike. Surprisingly, none of that stuff is crucial to the actual operation of the bike. The signals and lights and dash just don't work.

I'm not sure what approach I'd take. If only it were easy to scope the DC-DC inputs and outputs when the problem recurs.