Stop Start Auxiliary Battery Error

[Firstthebanker]

Hi Eveyone.

I have a 2017 C220 Executive Estate.

I have been searching for days online but can't find conclusive proof of what I need so thought I would try here.

A while back I got a message saying "Auxiliary Battery Failure" on the dash and the Green A is Yellow and stays Yellow, for 99% of the time it is Yellow, Occasionally it goes green and works for a couple of stop starts then goes days and days before working again. I drive 2000 to 4000 per month. The care has done 113k. Everything else works as it should, only the stop Start function doesn't work.

From the research I have to it is most likely the Auxiliary Battery. But I cannot find where on my car it is and the correct part number and if it is a DIY part.

Any help is most appreciated.

Thank you

FB

 

[keith of kent]

On the N/S B post is a sticker with a QR code. Scan it with your phone and it tells the location of batteries within the vehicle

 

[rayaans]

It's in the passenger side footwell. Needs carpet removing but doable

 

[Firstthebanker]

On the N/S B post is a sticker with a QR code. Scan it with your phone and it tells the location of batteries within the vehicle

Thank you. It shows me 3 LOL

 

[GeeJayW]

It’s a common problem. It’s not a battery, but a capacitor/power module located in the passenger footwell.

Here’s a few links that may be of interest:

Axillary Battery Malfunction | Parts, Maintenance & Servicing

My Mercedes c class just had that wording pop up with red beeping flashes which turned to a white colour with no beeps. Any idea if it's safe to drive with this or does it need to be looked at asap

forums.mbclub.co.uk

C-Class 220 CDi (W205) (2015) - Auxiliary battery problem | Electronics and Audio

This question relates to the above C-Class, just under 4 years old, with only 23,000 miles on the clock. The "Auxiliary Battery Malfunction" warning flashed up on the instrument cluster a couple of days ago. Although the warning isn't critical - and the car is perfectly driveable - the warning...

forums.mbclub.co.uk

 

[Firstthebanker]

It’s a common problem. It’s not a battery, but a capacitor/power module located in the passenger footwell.

Here’s a few links that may be of interest:

Axillary Battery Malfunction | Parts, Maintenance & Servicing

My Mercedes c class just had that wording pop up with red beeping flashes which turned to a white colour with no beeps. Any idea if it's safe to drive with this or does it need to be looked at asap

forums.mbclub.co.uk

C-Class 220 CDi (W205) (2015) - Auxiliary battery problem | Electronics and Audio

This question relates to the above C-Class, just under 4 years old, with only 23,000 miles on the clock. The "Auxiliary Battery Malfunction" warning flashed up on the instrument cluster a couple of days ago. Although the warning isn't critical - and the car is perfectly driveable - the warning...

forums.mbclub.co.uk

Thank you. That was what I was guessing. Is there anywhere I can check that A205905341480 is the correct part for my car.

There are loads on the likes of ebay some original, some not. Is it one of those things that you should only buy original, I remember about 15 years ago, I purchased mass Airflow part and it because apparent very quickly that the copies were rubbish.

 

[Firstthebanker]

I've just spoke to my local MB dealer told me it's £182, but refused to confirm or to give me the part number.

 

[rayaans]

I've just spoke to my local MB dealer told me it's £182, but refused to confirm or to give me the part number.

Mb are annoying and won't give the part number. Just have a look at your current one or message dealers on eBay like Listers / mb Newcastle/ mb Edinburgh

 

[Firstthebanker]

Mb are annoying and won't give the part number. Just have a look at your current one or message dealers on eBay like Listers / mb Newcastle/ mb Edinburgh

I was trying to avoid taking it apart twice (lazy lol) and it's cold haha.

 

[Firstthebanker]

From the description it sounds like the correct part for my car I purchased this Genuine Mercedes-Benz A205905341480 Voltage Converter Auxiliary Battery | eBay

 

[rayaans]

From the description it sounds like the correct part for my car I purchased this Genuine Mercedes-Benz A205905341480 Voltage Converter Auxiliary Battery | eBay

Sometimes the part number can vary on different versions of the same car so it would have been worth contacting the eBay operating dealers who would have sent you a link to the correct one for which you could have used the part number.

I reckon most of these units are the same though so try it and see what happens. Sometimes for stop/start it's the 12V battery that's weak and causes it to never stop/start.

 

[Firstthebanker]

You could be right, but I would of thought other electricals would he showing signs and everything else seems to work properly. I'll update once I've flitted it. I am away on my jollies late next week so might not be for a couple of weeks. Thanks for all your help everyone

 

[markjay]

You could be right, but I would of thought other electricals would he showing signs and everything else seems to work properly. I'll update once I've flitted it. I am away on my jollies late next week so might not be for a couple of weeks. Thanks for all your help everyone

The starter battery may no longer be fit for Start/Stop but still work perfectly fine otherwise, so don't expect to see any signs of other electrical issues. Keep in mind that the starter battery needs to be able to start the engine dozens of times during a single journey, which is quite onerous, and this is why it will still function perfectly in all other respects even when it's no longer fit for Start/Stop.

That been said, on cars equipped with the capacitor instead of a lead acid auxiliary battery, if the dash tells you that the auxiliary battery has a fault, then it will almost certainly be the capacitor that's the issue, and not the starter battery.

(The starter battery may also have an unrelated issue, but you'll only know for sure after replacing the capacitor)

 

[Firstthebanker]

The starter battery may no longer be fit for Start/Stop but still work perfectly fine otherwise, so don't expect to see any signs of other electrical issues. Keep in mind that the starter battery needs to be able to start the engine dozens of times during a single journey, which is quite onerous, and this is why it will still function perfectly in all other respects even when it's no longer fit for Start/Stop.

That been said, on cars equipped with the capacitor instead of a lead acid auxiliary battery, if the dash tells you that the auxiliary battery has a fault, then it will almost certainly be the capacitor that's the issue, and not the starter battery.

(The starter battery may also have an unrelated issue, but you'll only know for sure after replacing the capacitor)

Thank you. I'll change the capacitor and see what happens. I don't know but would the A being yellow all the time also happen if it was a faulty starter or would be as you say more likely to point to the capacitor.

 

[HITECH]

Thank you. I'll change the capacitor and see what happens. I don't know but would the A being yellow all the time also happen if it was a faulty starter or would be as you say more likely to point to the capacitor.

What was the outcome of this?

 

[OneForTheRoad]

Thank you. I'll change the capacitor and see what happens. I don't know but would the A being yellow all the time also happen if it was a faulty starter or would be as you say more likely to point to the capacitor.

My stop start still went green after fitting a new battery and turns green after 500 yards if yellow. The capacitor pack on my GLC failed to work after I replaced the main battery . Error messages were constantly showing, so a fix had to be found. Fitted A205905341480 or similar. Now everything's working as it should .

 

[rf065]

Thank you. I'll change the capacitor and see what happens. I don't know but would the A being yellow all the time also happen if it was a faulty starter or would be as you say more likely to point to the capacitor.

The starter battery really needs to be almost 100% for stop/start to work, from memory mine would not work if the battery was 12.3v or below. My capacitor had already been changed under warranty, very common fault.
None of the other electrical systems complained.
It also requires both batteries or capacitor/battery, whichever system is fitted to be near perfect or it just does not go green.