Fluctuating and low voltages... BMS faulty?

[themishmosh]

So, for the past 4 years, I've had my radar detector in voltage mode (displays voltage). The past few months, I've noticed the voltage dip abnormally low while driving the car--as low as 11.9V. It also, on occasion, had been fluctuating wildly every few seconds. The battery was changed less than a year ago. With the car off, the battery voltage was lower than i've measured it to be in the past (12.1V instead of 12.6). I suspected either the alternator or the BMS (battery management sensor). I unplugged the BMS connector (ie. disabled battery management) and got a consistent 13.4-14.2V all the time while driving. I feel this test made it less likely the problem was with the alternator. Unfortunately, leaving the BMS unplugged results in an error code that pops up on the dash with every key start, and also may cause some features to be disabled when in sleep. I should also mention that i did check all the connections at the battery terminals for tightness and reboot the body control module that the BMS falls under. Also unplugged the negative terminal of the battery for 30 minutes. Nothing helped.

This is the BMS on my 2020 ST. For the life of me, could not find any info on the part# listed. Benny@LevittownFord to the rescue!

Original 2020-2022 Lincoln Aviator Battery Management System L1MZ-10C679-B | Levittown Ford Parts

2020-2022 Lincoln Aviator part # L1MZ-10C679-B - Battery Management System

parts.levittownfordparts.com

Here is the new part (relatively inexpensive):

Easy install. Since I installed the new BMS, voltages are what I would expect. 14.3-14.7V normally. After a long drive starts to trickle down, with a low around 12.6V. This is the behavior I have come to expect. It's been a month now, and so far so good!

Note: because I also run a powered subwoofer and dashcam battery bank, I just changed the setting for target battery charge from 80% (default) to 90% using Forscan.

 

[Sea_Ray]

FYI
In looking at the picture it looks like the cable could be bloated in spots. If it actually is that would be a problem.

 

[themishmosh]

FYI
In looking at the picture it looks like the cable could be bloated in spots. If it actually is that would be a problem.

Thanks. the cable is actually a pigtail cable for a trickle charger. I have the negative terminal to to the top of the BMS instead of battery negative terminal.