I had an earlier post seeking input on an intermittent Charging System Fault warning https://www.fullfatrr.com/forum/topic72464.html

After much head scratching and seemingly unnecessary expense (new battery, alternator, serpentine belt/tensioner), it appears the rather innocuous looking BMS module could be at fault for causing the intermittent warning I experienced. I did a google search and not many posts clearly identified the BMS as a likely culprit for the warning, though Andy Roo on this forum did mention it. Most research pointed to the alternator as the solution.

Since the cost was minor, I decided to get one and install it while waiting for the alternator to arrive. For a few days now, no Charging System Fault has come up.

I really don't know exactly what technically the BMS does, but assume it is reporting back to the computer what it "thinks" it is seeing as a voltage and if it is misaligned with the expected voltage, the warning is coming up. I guess they can readily go bad, hence why there are replacements being sold.

I wish I had tried this first instead of the much more expensive items. Just making this post in case anyone else with a L405 comes across a Charging System Fault but DOES NOT have clear evidence of a weak battery or alternator according to voltage readings.