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Thanks melzonk! Replaced fuse 448 started car, no more malfuction flashing! What can I do about my hair that I pulled out in the last fortnight🤣put you on my Christmas card list.
Auxiliary Battery Malfunction
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Fuse box under tailgate floor cover. Should be printout in fuse box, spare fuse are not inc, need 10 amp fuse, on my vevhicle only 1 10 amp fuse colour. Red in the box, hopes this helps. Robbie
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My 2016 GLC has just started with the auxiliary battery malfunction error message. I intend to check the fuse 448 first. The vehicle has always had issues with the eco stop/start function with the battery replaced under warranty in less than 3 years. I trickle charge the battery now if the vehicle is not used for a period of 2 weeks.
Tony Mac - can you advise if the Auxiliary Battery Malfunction Error has been resolved on your vehicle?
Tony Mac - can you advise if the Auxiliary Battery Malfunction Error has been resolved on your vehicle?
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Thanks for the information, I will check fuse 448 first. 👍🏻
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Same issue. I reinserted the fuse 448 which was not blown 5 months ago and the aux battery malfunction message remained. The vehicle has functioned without any issues whatsoever covering approx 1500 miles.
As I drive infrequently a trickle charger was connected 24 hours a day for the past two months (in winter) when not using the vehicle. This maintains the battery voltage level and the aux battery malfunction message no longer appears!
I have concluded that a low charge in the main battery may be causing the voltage regulator (auxillary battery) to set the Auxillary Battery Malfunction message. So that replacing the voltage regulator may not be the root cause of the problem.
Will continue to tricke charge in winter and will have to see what happens over a period of time?
My error message has now disappeared without any intervention other than driving the vehicle more.. I think it is safe to assume that in many cases the error message is a result of lack of vehicle use resulting in low main and aux battery charge states. Except that for Auxiliary, that gets charged during over-run. That is where your foot is taken off accelerator and the vehicle coasts. I guess that's one way of squeezing more economy out of the car.
You can see how it charges by scrolling down to the fuel consumption section ( charge is displayed on the left)
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i looked at the fuses in my trunk and didn't see any numbered 448? can anyone advise? i am in the US maybe that makes a difference? found it - resetting it didn't work
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found it and reset it with help from someone with a tool. still getting the error message. is it worth it to first try a new fuse?
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can anyone send a link for purchasing a new fuse?
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Hello Everyone! Just wanted to share my same experience with Auxiliary Battery Malfunction fault... GLC 2016 250D 4matic, left hand drive, 115 000 Km, 6 years old (just over a month of the extended warranty!) "Start/stop" feature stopped working even if the function turned on... not that it's the end of the world (normally I switch off... like a muscle reflex) I haven't found any other unusual behavior... I drove only 20km after the fault and replaced the unit on the second day. The original manufacturer is Hella, it is the same part number as MB's part number: A 205 905 28 09 
Talking to the main Mercedes dealership spare part department and an independent spare part dealership (one of the biggest chain in the country) there is no replacement part (don't get confused to noname Chinese un-labeled parts), only original manufacturer part... the new part number is: A 205 905 34 14 
and here is the fault: 
The electrolyte leaked from the capacitors on the PCB which caused shorting... nice burn smell after opened the casing.... No needed to replace any fuse or clear any fault code (for me) Good luck everyone!
Talking to the main Mercedes dealership spare part department and an independent spare part dealership (one of the biggest chain in the country) there is no replacement part (don't get confused to noname Chinese un-labeled parts), only original manufacturer part... the new part number is: A 205 905 34 14 and here is the fault: The electrolyte leaked from the capacitors on the PCB which caused shorting... nice burn smell after opened the casing.... No needed to replace any fuse or clear any fault code (for me) Good luck everyone!
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Hello Everyone! Just wanted to share my same experience with Auxiliary Battery Malfunction fault... GLC 2016 250D 4matic, left hand drive, 115 000 Km, 6 years old (just over a month of the extended warranty!) "Start/stop" feature stopped working even if the function turned on... not that it's the end of the world (normally I switch off... like a muscle reflex) I haven't found any other unusual behavior... I drove only 20km after the fault and replaced the unit on the second day. The original manufacturer is Hella, it is the same part number as MB's part number: A 205 905 28 09
i had a guy circuit check my fuse and he said it's fine. i am still getting the error message. i haven't changed out the part since i hurt my hand and it's in a cast and i'm not paying 2 hours of labor plus a part to fix something that appears to be irrelevant...
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