"Malfunction Visit Workshop" / 12V battery life / speed sensor and coolant delete

Hello, I have a 2017 B250e with just over 20,000 miles, purchased six months ago. It had one previous owner, is in excellent condition, and drives beautifully. However, I recently got the "Malfunction Visit Workshop" warning in amber/yellow.

After reading forum threads, I see this could be caused by a range of issues from charging to the 12V battery or more serious coolant leakage. I have a dealer appointment scheduled but am troubleshooting in the meantime:

1) 12V Battery -- My Varta battery dates to mid-2016, so it's likely due for replacement despite no signs of failure.

2) Speed Sensor Check – Concerned about coolant leaks, I inspected the speed sensor (following this helpful QC Charge video). It looks clean, with no gunk or contamination, though I did notice a tiny bit of liquid that seems more like grease than coolant.

I’m attaching photos -- if anyone has insights or suggestions, I’d appreciate them! Looking ahead, I’m considering the coolant delete, but first I want to address the Malfunction Visit Workshop cause and figure out if I have anything to be concerned about now in terms of coolant leakage. Really enjoy this car and hope to keep it running for years. Thanks in advance!

I have no answers as I am new to this platform but I'm curious what advice you receive

An update: I took the car to my local MB dealer service center and had them pull the codes and swap the 12v battery, which was 8+ years old. I didn't have an opportunity to talk to the mechanic directly, but the codes had to do with the Battery Management System and the Charger.

Codes included:
BMS: P1C0700, U1C08F1, U1C0BF1, U1C27F1
Charger: U1923F1, U1912F1, U1914F1, U191AF1

The mechanic cleared the codes and said he re-seated some of the wiring which he suspected may have caused the codes initially. Based on my reading here and on a FB site devoted to the B250e, I'm inclined to think that the very old 12v battery may have been the primary culprit, but I don't have any hard evidence of that. I've driven the car about 20 miles since leaving the shop, and the codes have not returned. If anyone out there has any insights based on my original post, I'd be grateful to hear them. Thanks.

12V batteries are a problem in most EV's - they aren't generally charged while the main battery is, so they can go flat when you don't expect them to. And when they do, they throw up all sorts of errors because some components will be "more lenient" to a low voltage than others. You don't see the battery degradation as you do in an ICE car because you never pull serious current, the voltage just tails off and you get a problem which kills the car. Replacing the battery with new will likely have fixed your problem, but it's worth keeping an eye on the 12V level in future anyway.
You can do this without special tools, just your car key: https://www.mybclasselectricdrive.com/threads/how-to-access-the-secret-menu.1818/
The "UB" on the "Vehicle Data" menu is the 12V: if that drops below 12 you need to either charge or replace the battery. It will charge from the 400V circuit while the vehicle is driving.

Your car is under 30K miles and your speed sensor is clean then it is good to do a coolant delete to keep it for a long time. My B250E had dealership replaced the motor under warranty at 45K miles due to the coolant leakage seized up the rotor. When I learned about this issue at 80K miles, I checked the speed sensor cleanness and did the coolant delete myself. It seems that you have mechanics skills to do the coolant delete work. I summarized up what I did on mine on Post #2 on Dec 8, 2024 for reference. For the message displayed prior to the 12V battery replacement, it was the true culprit. When you turn on the car, not started yet, the voltage needs to be 13.8V. After started with its display "Ready", the DC converter would charge your battery and display 14.8V. After your battery replacement and these two conditions are satisfied, the message is still showing up then don't bother with the coolant delete since the the motor has some problem already.

If the 12V battery is not charged during a charging session how does it get recharged?