susanm

I have a 2015 c class 4 matic and I get auxillary battery malfunction. I called the service department and I am still under warranty but I cannot bring in the car until a week from now. The service department told me that this is the secondary battery and that is all I was told. Does anybody have this message appear and is my car safe to drive long distance?

christyan78

Try searching the forum,there was another topic for that,not long ago.
I had it,but it disappeared by itself.
From what i heard,it' s not from the battery as the w205 doesn't have an auxiliary battery.

DBOC205

With some models there is an additional battery for the ECO start/stop in the front foot-well area near the bass speakers. It could be related to that. Go to a dealer and get an XENTRY diagnostic scan done on the vehicle.

marmutz

i do have this problem.. if your start stop sytem still usable.. it's the voltage converter.. mine was the voltage converter..
At first the mercedes mechanic change the aux bat (turns out.. it's not battery.. it's a capacitor chip for w205)
For about 2 days the error was gone.. and it turn back the same error.. they change the voltage converter and no more problem till today..
All covered by the warranty..

dieseldoc

Just had this problem with my GLC. Eco start stop stopped working. Bad main battery/regulator/capacitor. All fixed under warranty. There is no extra battery. Codes were present in Xentry

Merlin1

Had this problem a few months ago, first had red message then white by the time I took car to dealer the message disappeared. Dealer replaced capacitor as above post, W205 does not have an aux battery.

Jooya

Hi.Please show me the location of the aux battery/capacitor.i can't find it 😞 And please help me about voltage converter. I have this massage in my car and can not go to dealer.

benzw205

Hello,


Sorry, how to change this auxiliary battery ? I do not understand where it is.

Thank you.

dieseldoc

Would take to dealer and have them fix it. It is not a do it yourself job.

evillavi

this is a DIY procedure for sure, I just finished changing mine. I have a W205 C300 2015 and the auxiliary battery malfunction message came up about 2 months ago. I was told by the Mercedes benz technician that it was not critical. The repair is covered under warranty, however I'm not able to take it to the dealer so I decided to purchase the spare part online (parts.com) for $104 with shipping included.

I went ahead and did it in about 35 min. the steps are:

1. Remove the cover under the glove compartment, this is a single screw and 2 clips
2. There are 2 cables attached to the cover (bulbs) so you have to disconnect both cables.
3. Pull back the carpet (carefully), it will be hard but the foam behind the carpet can be twisted without any issues
4. there will be a plastic cover with 3 nuts, you have to take them out and remove the plastic cover. You will see the voltage converter right there, which will be attached to the metal piece by a clip and a screw. Carefully remove the nut (Carefully and slowly). and just unplug the converter and replace with the new one and follow the same procedure in reverse.

Be careful with the tools as there are many DC cables under that carpet, so you can easily create a mess if you are not pretty careful.

I did not take any pictures with the details, but it is the same as the one posted earlier here

If you have any questions on this particular one just let me know

Regards

Hamie

Hi,
Can I still drive the car for a week after seeing the 'auxiliary battery malfunction' message?

evillavi

yes, i drove it like that for over 1 month, perhaps 2. I checked with the MB technician before doing so

Regards

eduardo

J.electroauto

Hii.men i have this problem in my W205 c220 diesel 2015 plz can you seen me 1 foto of the location aux battery

giowoo

Hi, I have checked under the glove compartment, I didn't found any capacitor,there are nothing under the plastic. Can you show me which exactly it is ？

benzw205

Thank you so much !

PRINCE T

Great post post but I have a few questions.

I drive a 2015 C300 base 2.0 lt

I've been having this same issue for about 5 months now. It occurs and sometimes disappears for a couple of weeks.

1. can you kindly give us the part number to search for or a direct link to the 104$ part you purchased?

2. is there a picture of your old part so I can know exactly how it looks like.

Thanks in advance

Pkinsella

Gaz80mcc

Hi been reading through a few posts regarding Aux bat malfunction message. Ive got a 2015 c220 estate amg line and I got the message last month so I've had the voltage converter replaced and the message went away and everything was fine and working as it should. But the end of last week the message came back on this time flashing red then to white and has stayed on since. I've checked everything and it's all working fine still even the start stop is working great, I've even checked my main battery to make sure it was fully charged. So just just wondering if anyone as got has got any ideas on it. As car is out of warranty now. Thanks

John Mocali

Hello, considering the number of complaints you find in the different forums one might think that the product is defective!
First models were shipped with a voltage converter with part no. A 205 440 00 73. Such model has been replaced by a new part no. A2059052809.

I got mine changed less than a week ago. For those interested in what happens to your voltage converter there you go:



If you want to know where it is this is a print I got from the dealer.

If you are experiencing again the problem go back to the dealer and ask for a XENTRY scan. Hope this helps.

itaolaf

Hi, I have a C220 Bluetec W205 and the AUx Bat malfunction red alarm came on then after driving the car for a while it still flashes but only white. The start-stop function does not work and I read on this forum that if that works is not the Voltage converter. I have located and unplugged the voltage converter and the alarm is still flashing white when I stat the car. According to you should I still change this part, which is quite expensive here in South Africa and I cannot locate it on Parts.com as you suggested. Please advise

Cosworth2000

This battery is for the Eco Stop/Start function. It is recharged when under break load. You can normally see it as "charging" when you look at the meter which shows how much L/KM you are using.

itaolaf

Hi Cosworth2000,

Thank you for your response, can you please tell me where this battery is located and does it need to be replaced rather than the Voltage converter?

Greg52

Greg52

parkwood

I have had the warning message on a 2015 250d 4matic at about 30mths 30km. Garage replaced the "battery". Warning sign gone. This was about 6 mths ago.
stop start had seemed to work less. Initially stop start was back but all over the winter it did not work but i cover short distances and drive in an anticipatory style so do not brake heavily.
after a long run this week and in warmer weather stop start has come back after a few km.
so your use and driving style as well as ambiant temps also seem to be a factor.