Auxillary Battery Malfunction

[Ovlov440]

Hi all

I have had the message 'auxillary battery malfunction' pop up in the display on my 2014 CLS250 a couple of times in the last week. Car is running fine, no issues with the start/stop system. Battery is reading 12.87v (without the engine running) so would appear to be healthy. I have a generic code reader and that is showing no codes at all.

Assuming the battery is good, are there any other things I should be looking at as the source?

Ta

Ade

 

[Diesel Benz]

I guess you have the motorcycle size aux battery for start/stop? My W222 has one and the aux battery does not seem to survive much more than 3 years. Voltage is perfect and no internal leak. But the diagnosis tool reports too high internal impedance at the battery (voltage drops too much when loaded).

Odd if stop/start still works fine on your car, mine drops even distronic cruise (no connection to the battery fault but this way the owner will take care of the fault to keep emissions ok).

 

[geoffus]

Put the battery on a smart charger for a few hours, if the message stays away for a few days then the battery is at fault.
I had the same problem, after charging the message has now disappeared and not returned.

Auxilliary Battery | Electronics and Audio

I had a warning stating "auxiliary battery malfunction" come up on my display, as you do, googled it & decided to replace the battery itself (located in boot, so easy job to do). Started to look around for costs & found on Europarts for £138.00, closely followed by another part supplier for...

forums.mbclub.co.uk

 

[KillerHERTZ]

Battery is reading 12.87v (without the engine running) so would appear to be healthy. I have a generic code reader and that is showing no codes at all.

That reading will be your main battery, not the Aux.

 

[Ovlov440]

That reading will be your main battery, not the Aux.

I did take the reading diretly from the terminals of the aux battery in the boot.

 

[Diesel Benz]

My W222 AUX battery had a very good voltage but I test-loaded it with a 21 W bulb and the voltage dropped below 11 V. The battery is supposed to handle really much higher load. If the voltage is good, I'd try to load it if the battery is easy to reach (not so easy on the W222).

 

[Ovlov440]

My W222 AUX battery had a very good voltage but I test-loaded it with a 21 W bulb and the voltage dropped below 11 V. The battery is supposed to handle really much higher load. If the voltage is good, I'd try to load it if the battery is easy to reach (not so easy on the W222).

Will give that a go, thanks for the advice.

 

[John]

You will need to take the boot lip centre trim off to then be able to access the right hand side behind the trim where the aux battery is.

From memory, I don't think removing the trim at the front of the boot (so behind the rear seats) was necessary to access the aux battery.

I took the opportunity to wire in some terminals so they could be threaded through the fuse hatch.

Now I fully charge my aux battery every 3 months to keep it ticking over.

Main battery is on a trickle whilst I am not using the car much at the moment.

 

[Muckypaps]

You shouldn't read to much into the battery voltage it is showing, mine was reading 13 volts but the capacity was just about nil.
Fitted a new battery and the problem was solved.
The electronics on your car is telling you the battery is knackered, so maybe it is.
It isn't an expensive item to replace, you'll spend more time overthinking it when it's a very easy fix.
Have faith in the advice the car is giving you.

 

[john b]

can anyone tell me where the aux battery is on my 2012 cls 350 cdi, if it has one!, it is not in the dash where wis/asra states

 

[KillerHERTZ]

can anyone tell me where the aux battery is on my 2012 cls 350 cdi, if it has one!, it is not in the dash where wis/asra states

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[john b]

to my own question, this battery is on the drivers side of a right hand drive car. Remover the side panel of the dash and remove the panel below the steering column, there is a 6 mm bolt that is behind the side panel, undo this and the battery and attachment bracket will fall down.
Just as wis/asra states, but they show a left hand drive, it is exactly the same for the right hand drive but on opposite end.