Auxiliary Battery Failure

[Glasseyefong]

I have a 6 year old S350d that has done just 13000 miles. The above error message came up today while waiting at traffic lights. I can see why stop/start no longer works but the Hold function is also not working now. I regularly trickle charge the car overnight but don't know if that also charges the auxiliary battery. I have noticed that a couple of times recently when starting from cold, the brake pedal has been very hard to depress but don't know if this is related.

I guess that it will have go into a garage again for yet another fix but any ideas as to whether this might be something other than battery failure?

Martin

 

[Big Cheese]

I have just changed both my batteries in the last two months, have had them coded to the car but I still get auxiliary battery malfunction coming up on the dash.
I know the batteries are good so I am ignoring for now.

Sent from my Pixel 7 Pro using Tapatalk

 

[malcolm E53 AMG]

You really need to buy a multimeter set it to DC and check the voltage of both batteries they should be registering around 12.6 volts engine off and 14.8V engine running any reading below 12.2V will likely cause problems with the electronics - even new batteries can be problematic especially if they are not fully charged when fitted or just plain faulty

 

[Glasseyefong]

Thanks for the responses.

Malcolm - I looked on line at assorted manuals and Youtube videos but am no clearer as to where the aux battery is located. Is it in the boot on the right hand side behind the lining?

 

[malcolm E53 AMG]

This might help!

 

[Glasseyefong]

Thanks for that. Not the easiest access. Hopefully my local MB garage will already know where it is.