I have had the aux battery failure, and replaced it myself, however I still have the white failure message coming up. I have in the past had the red message too. All stop start functions are working, I just have the annoying message which keeps popping up every 5 or 10 seconds. Does the error code need to be cleared using Xentry, by MB?

When I replaced mine the message disappeared immediately, needed no resetting

Thanks Greg , was your nag warning only white? I had heard others say this but wondered if the fact that mine went to a red warning that might have been flagged as more serious and need resetting.

You don't need to reset the code. Once you change the battery, the message should resolve. Maybe try an OBD scan to see what other codes there are?

it was several years ago but my memory was that it started off white and after a week or so went to red , do you push the ok button on the steering wheel to cancel it?

Yes, the message goes away when OK pressed, but starts going on and off again every 15 seconds (ish). I haven’t tried holding the button down tho’.

I fitted a remanufactured one and it has been working fine since, was yours OE new or remanufactured?

I think maybe not MB orignal, surely that’s not going to be the issue?

aftermarket auxiliary battery? Surely it might be the issue...

is the fault exactly the same now as to when the original unit was installed? Your start stop function is working now, was it still working with the original failure?

I had an auxiliary battery malfunction note appearing on my dashboard i went to the dealer they changed the auxiliary battery and the note disappeared.

I was advised that the main function of the auxiliary battery was to facilitate the Stop/Start function but before I replaced it I had to buy a main battery and immediately the Stop/Start function sprang into life and has worked faultlessly ever since. The auxiliary battery malfunction message still flashes every few seconds despite having had a scanner try to clear the code. I then fitted a new replacement but no luck, the message still persists, to my great annoyance. As all functions in my W205 C Class are working I am tempted to learn to live with the irritating message flashing constantly. Unless someone can tell me what else I can do to solve this issue.

oem auxiliary battery to be replaced at your dealer if the message still shows up let them deal with it.

I think your problem is somewhat unique and I doubt anyone here would be able to assist. Shame you couldn’t get a warranty on the original repair, I understand a reluctance to visit the dealership but other than putting up with the error message this may be your only avenue, good luck

I am having the same problem, I replaced the auxiliary battery with a Mercedes OEM part and still have the message. Tried clearing it with my scan tool and does not go away.

I'm not sure exactly what your issue is, but I know it's a safe bet that if you clear a fault code and it comes back as a new active fault, the issue is not resolved.

I had my Auxiliary Battery replaced under warranty and had no further issues. I'd assume there is something else amiss if you are still getting active codes. Does your main battery load test check-out okay?

Good luck!

I put a new main battery in about 6 months ago and load tested it and was ok. I was watching a video about the auxiliary battery and they also mentioned something about a fuse under the rear trunk and when I pulled it out it looked pretty dark/burned. I will pick one up tomorrow and hoping that will solve the issue.

Turns out the fuse solved the problem. As soon as I put the new fuse in and started up the car the warning message was gone. If anyone runs into this problem where the "Auxiliary Battery Malfunction" warning message does not go away even after replacing the part, check fuse number 448 located in the trunk under the cargo floor to see if it needs to be replaced.

Well done you

Hi,
I took my vehicle to a MB independent specialist who was able to clear the fault message, unfortunately I cannot recall the cost but confident it was much less expensive than the main stealer.