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Anyone get this error yet? Seems this needs to be replaced every 3 years and I've had my car since 2017.
Where can we buy this part and price? (looking for Mercedes genuine part)
Where is this battery located? (I think it is in the front passenger foot area)
Just got the error within the last month (at 5 years and 25K miles).
I've read that it's not really a battery but a capacitor / voltage converter, and should be replaced whenever the battery is.
I'm surprised that, at 5 years, I still have the original battery, especially in Texas.
I learned from my BMW-owning friend that spending $20 on a headlamp vs. $400 at the dealership, if an error in judgement, would have to be made 20 times before it cost as much.
I'm still haven't decided if I'll apply the same thinking to one involving my C300's electrical system.
I followed the instructions from the video, and replacement was pretty easy.
I'm handy, but car work is a pain if it's not your everyday, and it only took me 45 minutes total.
I had some different experiences with my 2017 C300 coupe from the video I'll share here, and post more about the damaged unit.
Generally:
- I also found only 1-T15 screw, like the video. It may not be uncommon.
- All of the nuts are 10mm, including the one that holds the aux batt / voltage converter. No 8mm socket was needed.
- Deep sockets and an extension are helpful. The studs are set back far enough to be annoying.
- After loosening with a socket, I removed the nuts by hand to avoid having to dig for them.
- The connector to the aux batt isn't very clear on the video. I have a pic below to help explain it.
The error message that first comes up red, then annoyingly pops up every 20 seconds or so until it's fixed.
There was only 1-T15 screw, and it's on the right side. It's worth checking the left side for a screw, but it's tucked up pretty well, so don't be surprised if there isn't one.
The video says to "press down," but it doesn't say what. The correct action is to pull the white tab out (away from the unit, as shown), then push down on the tab (toward the wires) and pull the connector loose. If you look at a new unit, you'll see a triangular tab on the socket, which should give you an idea of what you're trying to get free of.
Oh yeah, the circular thing behind the aux battery mount is the bass speaker. If only it was the singular issue for the car's audio quality...
I took the old unit apart to see what kind of "battery" this thing is. It's not, it's a board with capacitors.
4 of them are 2.7V 50F, so I'm glad I didn't touch the contacts and discharged them before handling *.
I still don't know why there's a core charge if you buy it from Mercedes. There, it's $137+tax+core, which is about $152.
I got mine from eBay for $40. So far so good.
The first thing I noticed when I removed it was that the part number is different: A205-905-28-09.
Fortunately, research shows that the 205-905-34-14 is a suitable replacement.
The YouTube video says to check the replaced unit for dark brown or black marks from overheating or burning.
I didn't see anything significant, but upon opening it *, it's clear that the board was burned.
You can see a slight dark circle in the middle image, so more detailed inspection may be necessary.
In the last pic, you can see that one of the capacitors is popped.
I checked fuse 448, labeled "Automatic Transmission" in the fuse allocation chart.
It wasn't blown, but I think I'm going to check for others in the next few days.
I also don't know if the error will clear itself or if I'll have to take it to the dealer (not tested yet).
I'm due for regular maintenance anyway, so it shouldn't be a big deal.
The old aux battery, the bottom, and with the bottom removed. *
Note the left front white capacitor is popped. Not sure if that was cause or casualty. They're 2.7V 50F each -- not kid stuff. *
*DISCLAIMER: Like a car battery, charged capacitors can kick your butt or even kill you.
If you don't know what you're doing, you probably shouldn't be doing any of this.
My actions are my own, and yours are yours.
Hi Antigeek, thank you for your detailed post. I am going to try not geeking too much.
I side with the bulged shorted cap killing its charging circuit.
Charging 50Farad is nearly like driving a short circuit with a high current. I guess the limitation circuit is not smart enough to enforce any limits
-Or the module gets killed by the unfiltered voltage spikes (radiator fan, fuel pump) 2.7Volts is a very narrow limit to work with.
We know the OEM design is cutting it short. To play around with fixing this module, I would increase capacitor Max voltage to 3.3V and decrease capacity to 40F for size fitness... before it gets all coocked!
as seen on eBay...
Last edited by CaliBenzDriver; 10-29-2021 at 04:08 PM.
Reason: pic
06-14-2020, 12:21 AM
