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Discussion Starter #1
Trying to book car in for MBUX media screen fix. Currently have a black screen and can’t do anything. In car phone charging isn’t even working.

Auxiliary battery is being reported as malfunctioning. Which could be the root cause. Wouldbt be supprised being a 68 plate sitting in showroom / out back somewhere for a year doing nothing.
 

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I was surprised to hear that the A Class has an Aux battery as I hadn't see one anywhere. My SL has two batteries, a start battery in the engine compartment that is only used for start and is then disconnected and a full sized Aux battery in the boot that deals with else.

Having failed to find anything anywhere I did a quick search and found this https://thebatteryshop.com.sg/auxiliary-battery-malfunction-mercedes-benz/
and it seems that the Aux is just a small, probably a 1.2Ah, sealed lead acid battery.

I can understand the two batteries in my SL but I cant see why MB use this little aux battery but I'm sure there is a good reason for it
 

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So that in the event of your starter battery being dead and you not being able to start your car, you can still:

use SOS
Alarm & Immobiliser still protects the car
Unlock the car and get in
Release the park brake if you need to
etc.

The Aux battery will still support essential/useful functions, should your main starter battery die.
 

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Discussion Starter #5
"You will also realize that your auxiliary battery is malfunctioning if your car engine starts and works well, but your car accessories which runs on voltage such as the car audio system, signal lights or your vehicle’s safety feature like PRE-SAFE, Active Brake Assist, ATTENTION ASSIST, Blind Spot Assist, Lane Keeping Assist, Lane Keeping Assist, Night View Assist PLUS, Active LED Lighting are not working.

Additionally, eco start-stop and fuel consumption might be affected too. Therefore, whichever signals of malfunction that you are getting, is a sign that it’s time to replace the auxiliary battery."

Makes more sense now as a few of the cars feature like speed sign recognition and active lane assist would work for a couple of mins and then stop. I still think this could be part of the problem with the main nav screen not working, Mercedes seem to think otherwise and are getting in touch with Germany as they think it a control unit problem. They tackled the screen not working issue without replacing this battery first, which is madness. I had a bit of a go and said logically this should have been the first thing they should have done in trying to diagnose the problem. The guy on the phone went away and come back telling me the technician knows what that issue is and decided to not do that first.

What's the bet I was right and magically the control unit issues are fixed tomorrow.?
 

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They tackled the screen not working issue without replacing this battery first, which is madness. I had a bit of a go and said logically this should have been the first thing they should have done in trying to diagnose the problem. The guy on the phone went away and come back telling me the technician knows what that issue is and decided to not do that first.
Clearly logic is not prerequisite for a mechanic these days. On the other hand a black screen may be a well known fault so he got on with that first, after all he can always refit the control unit if that doesn't fix it and then replace the battery thereby charging MB for two jobs 😂
 

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Discussion Starter #7
This is with Mercedes :p the black screen is indeed a known issue, usually on the binnacle display, this is something I have not seen any reports of, this only affects the nav screen, I can get it to partially display a car graphic when searching for a parking space, apart from that and the Mercedes-Benz boot up logo, nothing.

Ahhh, well not a lot I can do but wait and let them **** about with it. Going to get a courtesy car tomorrow and milk them for something at least, hopefully, should make it go a fraction quicker.
 

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Discussion Starter #9
Under the passenger foot well. Pull the carpet back and you will see some of the wire and a plastic cover that needs removing.
 

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very nice, i will go check it out, thanks!

i'm going to plug an battery maintainer to the starter battery first, because, if i don't drive for a week, i can see the starter batter is only 70-80% left
 

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My 2015 A180 developed a faulty auxiliary battery. The car was unable to diagnose the problem, no error messages, not even on the memory. I tryed to charge the battery, open circuit voltage was aprox 13V. In practice I can confirm now, if I connect a 21W bulb to it´s terminals it immediatly drops to 8V.
In my case everything was normal, but the car was unhable to recover from a Start Stop event, flashing like a Christmas tree. Now it makes sence but reaching the root cause was not easy at that moment.
Root cause?! According to the electrician, he found a groung cable near the área where the battery is, that had high reistence and could be causing an erratic battery charging control. But this is just a ghost, not possible to establish the cause - effect relationship.
As said, this battery is under passenger feet. Just pull up the carpet and all it takes is 10' to replace the battery.
In W176 it´s necessary to fitst remove the cabin filter case cover, in order to gain space to remove the battery cover. But it can be simply pulled with the fingers is a couple of seconds. Really easy!
 

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My 2015 A180 developed a faulty auxiliary battery. The car was unable to diagnose the problem, no error messages, not even on the memory. I tryed to charge the battery, open circuit voltage was aprox 13V. In practice I can confirm now, if I connect a 21W bulb to it´s terminals it immediatly drops to 8V.
In my case everything was normal, but the car was unhable to recover from a Start Stop event, flashing like a Christmas tree. Now it makes sence but reaching the root cause was not easy at that moment.
Root cause?! According to the electrician, he found a groung cable near the área where the battery is, that had high reistence and could be causing na erratic battery charging control. But this is just a ghost, not possible to establish the cause - effect relationship.
the first thing i'm get into my A250, is to turn off that engine auto start/stop, turn off any unnecessary power usage
 

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Discussion Starter #13 (Edited)
The part (MBUX control unit) seems to have arrived, just off the phone and been told this is being fitted, coded and updates being done to various parts of the car's systems. I need to call back at lunchtime tomorrow to see if it is ready and if I can collect it. :) Fingers crossed. I cannot wait for the full MBUX experience. Be nice after a 16 week wait to have a car, and a functioning one at that.

I emailed MB UK Re: My original factory order falling through, lack of comms during the order wait period, no build slot after 14weeks and the issues with this so-called "New" working car they supplied me with. Being investigated now. I cheekily asked for some form of goodwill gesture as compensation, I hinted a free service plan and Carplay upgrade may make me forget all the woes and put Mercedes right with me.

I also did the same process with the lease company who are also investigating what they can get for me as compensation. Lease company should also be in contact with Mercedes so hopefully, the cases cross paths and I get something out of one of them as the level of service I have received from the start has in my mind been atrocious. I don't care who us at fault now. I'd hate the process I went through to happen to someone else so I thought I'd try to not let either one off the hook.
 

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I do fell sorry for you, it does take the gloss off having a new car, I have had a few minor issues to deal with, and at times I wished I never sold my old car, still hope all goes well for you now though.
Just one question, is the auxiliary battery self charging, wonder what the life span is.
 

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find your auxiliary battery, test the voltage before and after your drive, i think it should be self-charging, but those battery do fail, i'm thinking about how to keep this small battery charged
 

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Discussion Starter #16
Have no idea what state the aux battery was in, it did throw up a malfunction message and I now know it was causing issues with speed sign recognition and active break assist, was gong to rip it out and take a look but thought best not mess with it, I was also going to try to find the fuses for MBUX systems and remove those along with the main battery, again being a brand new car I thought best let Mercedes deal with the issues rather than **** something up and having no leg to stand on.

Someone posted a link to the Aux battery functions somewhere and after reading that it appears It is connected in some fashion to some of the cars safety featuresso a malfunction on that could cause a whole heap of issues, that should have been fixed/replaced too.

Another issue Ive been reading about is the aircon and temp sensor issues, I think I could potentially have some of those issues too so it may well need to go back in at some point if they have not checked and fixed if needed, which I very much doubt they have as I failed to mention it, I’m hoping it was just me not being familiar with the system being new to me, I had no visual feedback on fan speed and actually temp setting. Besides that would take another week to investigate and fix, I have to have a car this week as my partner could go into labour at any moment now.

if not ready tomorrow as they suggested it would be I am going to get a loaner.

Cross all your fingers and toes for me.
 

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i think the aux battery is somehow relate with the main started battery, so in this car, we need to keep the main battery charged all the time, if you don't drive for a week, the main battery lose voltage, i think it might affect the aux battery, and if you do that often, the aux battery might develop some problem. for battery, always keep it charged at full. i'm going to have a charger connect to main battery if i'm not driving it for 2-3 days.

for the fan, are you talking about radiator fan?
 

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Discussion Starter #18
🤣 Mercedes are a joke, I was told yesterday to call back today as the part had arrived and coding/updates needed doing. I just called for an update to be told by someone else it appears the part has not arrived. Which is it? I have asked the lady to check with the workshop/technician. My experience just gets better and better.
 

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🤣 Mercedes are a joke, I was told yesterday to call back today as the part had arrived and coding/updates needed doing. I just called for an update to be told by someone else it appears the part has not arrived. Which is it? I have asked the lady to check with the workshop/technician. My experience just gets better and better.
usually, if you delay your expectation, for longer time, you will ok with what you got, i'm not looking forward to get my car back this week, it's already 3 weeks at dealer, waiting for turbo.

i have told the dealer, "take your time, make sure everything is correct" usually i don't push them.
 

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Discussion Starter #20
I have a million things to do at work before I go on holiday / paternity, my other half is about to give birth. I estimated end of this week and my advisor said, na, before then. So I had reasonably set expectations. I called and said get the car ready as I want it back until the part arrives. Not being f’d about by Mercedes any more. I hate them already and Ive has the car since the 25th and only driven the less than a week. 😂
 
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