Auxiliary battery malfunction

Page may contain affiliate links. Please see terms for details.

hedgehogsdad

Active Member
Joined
Aug 8, 2018
Messages
177
Location
Chester
Car
Mercedes C63 AMG
Hi,

I've got the above warning showing in my '16 plate C63. When I started the car this morning, the warning was in red, but after driving for a short while it went to white. Oddly, the stop start function is working fine and the car is running perfectly. Does the warning appear if the Aux battery is low on charge, and if so, why hasn't the message stopped not it seems to be ok again?

Help appreciated
 
It’s not uncommon for the auxiliary battery (which is a capacitor located in the passenger footwell) to need replacing. Ours was replaced under warranty in 2018. There are several versions, but this is what it looks like.

8C0235C6-FB66-4FDD-9AB9-0E1A5D97A90D.jpeg88BE202E-4E0D-4B2C-92FB-0C22490BFF2E.jpeg
 
Auxiliary battery isn’t covered in the extended warranty. Had a similar problem a few days back. Also here’s a list of what they do and don’t cover.
That is what I understand, however, the Aux Battery in the newer C-Class is actually a capacitor in a blackbox. I wonder since this is 'solid-state' electronics if this is actually covered since it is clearly not a consumable item like a normal battery.
 
That is what I understand, however, the Aux Battery in the newer C-Class is actually a capacitor in a blackbox. I wonder since this is 'solid-state' electronics if this is actually covered since it is clearly not a consumable item like a normal battery.
Good point. Also would you recommend getting extended warranty? In all my years driving I’ve only ever had problems which are listed as being not covered by the warranty. What exactly am I paying £700 a year for?😅
 
Good point. Also would you recommend getting extended warranty? In all my years driving I’ve only ever had problems which are listed as being not covered by the warranty. What exactly am I paying £700 a year for?😅
I'll let you know how I get on. They have confirmed that the diagnostic (£168) will be covered as a minimum, but no confirmation regarding any other costs.

Fingers crossed
 
Good point. Also would you recommend getting extended warranty? In all my years driving I’ve only ever had problems which are listed as being not covered by the warranty. What exactly am I paying £700 a year for?😅
Yes, I would recommend the extended warranty since the cars are getting more and more complex, requiring special parts and tools to repair if something goes wrong.

In my experience, the extended warranty was £850 for a two-year extended warranty from MB, so considerably cheaper than the £700 per year figure you quoted.
 
I'll let you know how I get on. They have confirmed that the diagnostic (£168) will be covered as a minimum, but no confirmation regarding any other costs.

Fingers crossed
Well good luck and please report back your results on this claim. Thanks
 
Quick update. Just driven to my office and back to pick up some stuff and the warning message has gone. Looks like I must actually have a battery and the longer drive has charged it sufficiently.

I'll leave my booking in place for a week to see if it happens again, but fingers crossed it was as simple as that!

Thanks all for your help
 
You definitely have what Mercedes calls a voltage converter, basically a big capacitor, in the passenger footwell attached to the prefuse box, I think you might also have the AMG computer down there somewhere so might want to be a bit more careful.
Changing that yourself is quite simple, just pull the plastic door sill cover panel (also the fuse box cover), unscrew one T20 from underneath the glove box, pry the glove box cover and then pull the carpet foam out.
After that use a 10mm socket to unscrew 3 screws from the protective plastic panel and you'll find what @GeeJayW linked, it should look something like what I've attached.
 

Attachments

  • P1050929.jpg
    P1050929.jpg
    247 KB · Views: 21
You definitely have what Mercedes calls a voltage converter, basically a big capacitor, in the passenger footwell attached to the prefuse box, I think you might also have the AMG computer down there somewhere so might want to be a bit more careful.
Changing that yourself is quite simple, just pull the plastic door sill cover panel (also the fuse box cover), unscrew one T20 from underneath the glove box, pry the glove box cover and then pull the carpet foam out.
After that use a 10mm socket to unscrew 3 screws from the protective plastic panel and you'll find what @GeeJayW linked, it should look something like what I've attached.
Thanks for the info, and as per my last update it appears to have sorted itself out, at least for now. How does that happen then, if it's a capacitor rather than a battery - i had assumed using it had charged the battery sufficiently but evidently not. Am I likely to have it happen again?

Cheers
 
Thanks for the info, and as per my last update it appears to have sorted itself out, at least for now. How does that happen then, if it's a capacitor rather than a battery - i had assumed using it had charged the battery sufficiently but evidently not. Am I likely to have it happen again?

Cheers
Exactly this happened to my W205 C300h - I have been in Hong Kong for an extended period (circa 9+ months). Left the C300h on permanent charger with a CTEK charger. Upon my return from Hong Kong, the C300h started up first immediately without any problems, but I got the dreaded Aux Battery warning on the dashboard.

Taking advantage of its remaining factory warranty (only two weeks left), I booked the car in with the local MB dealership. However, after driving the C300h around for two days, the Aux Battery warning cleared itself, and subsequently, the local dealership could not find anything wrong with it. The Aux Battery was therefore left unchanged and still working fine two years later to this day.

So certainly in my experience, the 'capacitor' takes considerable time to charge up.
 
Those capacitors will take quite some time to charge up, not sure on the hybrid but on the bog standard diesel when you switch your trip screens to the remaining mileage bit you'll have the green bar with Charge label underneath, it'll be full when cruising which means the capacitor is being charged, you'll want to keep it like this as long as you can to breathe some life into it.
If it works OK afterwards then you should be fine, although for the sake of at most £100 and 30-45 minutes work I would just change it to a new one rather than risk screwing with electrical system of an at least >£10000 car, way more in case of your C63.
 
Would you believe it, I started the car earlier and it's telling me I have an auxiliary battery malfunction again!!

I've driven the car, and the start stop icon is green, with the function working as it should do.

I don't want to take it into Merc for a diagnostic under warranty particularly as the car has an MSL map on it and I don't want to have to go through the process of swapping back to the original.

I suspect it will clear again in a day or two, can I just ignore it or should I really get it fixed??
 
Would you believe it, I started the car earlier and it's telling me I have an auxiliary battery malfunction again!!

I've driven the car, and the start stop icon is green, with the function working as it should do.

I don't want to take it into Merc for a diagnostic under warranty particularly as the car has an MSL map on it and I don't want to have to go through the process of swapping back to the original.

I suspect it will clear again in a day or two, can I just ignore it or should I really get it fixed??
So the error pops up when you turn the car on every time or it's gone again? If the error pops up the start/stop shouldn't be working.
I would check the voltage of your main battery if you have a multimeter, leave the car running for good 45-60 minutes, turn it off and check the voltage after around 5-10 minutes, if it's above 12.4V then that's OK.
If the problem persists I would just change the voltage converter with a new one, although not a big problem apart from the annoying pop up on start up and you could keep driving the car without it, I wouldn't personally want to take the risk as electrical systems in cars nowadays are a right pain to fix.
 
Hi, just had my aux battery (voltage regulator) as the dealership call it changed under extended warranty, problem is the dealership informed me it has not cleared the message fault, and if I want them to see what’s causing the issue they want £160 an hour to fault find, just wondering if it’s a good drive could cure the issue, anyone else had this sort of experience after changing the regulator.
 
Hi, just had my aux battery (voltage regulator) as the dealership call it changed under extended warranty, problem is the dealership informed me it has not cleared the message fault, and if I want them to see what’s causing the issue they want £160 an hour to fault find, just wondering if it’s a good drive could cure the issue, anyone else had this sort of experience after changing the regulator.
Mine is still showing the message even though the start stop is working and the symbol is green. My local dealership offered to cover the cost of the diagnosis under the warranty, but wouldn't confirm if that would also cover the cost of the aux battery. I think I'm going to have to book mine in again, although sod's law says that as soon as I do it will clear itself
 
If you have a W205 I can say you are covered under extended warranty for parts and labour my problem after swapping It out for a new one the fault message is still here lol
 

Users who are viewing this thread

Back
Top Bottom