ML350 W164 2010 Auxiliary Battery Malfunction

[pikeface999]

I recently had the message "auxiliary battery malfunction" come up on dash. So I have replaced the Mercedes aux battery with a YUASA NP1.2-12 12V 1.2Ah F4.8. However I still get "auxiliary battery malfunction"after a few seconds. I have checked the connections and battery voltage {12.75v).

I also checked the battery I took out and it looks ok 12.75v.

checked stats with scanner and that reports either defective or not connected.

Disconnected aux battery and exactly the same message, so it appears as if the battery is not being checked

Any ideas where to look next please.

Jeremy

 

[LostKiwi]

Here's a diagram of the layout.
Hopefully that may help.

Benz 164 Battery Control and On-board electrical system components

www.micro-tronik.com

 

[pikeface999]

Thanks, this looks like it might be the charging of the aux battery that's the problem. will give it some thought

might hook up a meter to the aux battery and start car and see if it changes, if not nmanually charge aux battery and see if the temporarily fixes it.

 

[pikeface999]

Found this very interesting

The DC converter that they offer to install is a fix for charging the aux battery, it is normally not present in any car.
The aux battery is normally charged from the N10 - front SAM and monitored by the same module, but if you happen to drive a lot of short trips, the front SAM can't keep up with the charging process so MB offer to install the DC converter, which is connected directly to the aux battery terminals in parallel to existing leads for plus and minus.
The DC converter is basically a small battery charger that feeds the aux battery with 13,2volts at 100mA (float charge level of battery), while your car is driving. it is important that the battery is not charged with higher voltage or current at this stage, otherwise it will cook the battery.

You may need to cut and past this url to see video

 

[LostKiwi]

Found this very interesting

The DC converter that they offer to install is a fix for charging the aux battery, it is normally not present in any car.
The aux battery is normally charged from the N10 - front SAM and monitored by the same module, but if you happen to drive a lot of short trips, the front SAM can't keep up with the charging process so MB offer to install the DC converter, which is connected directly to the aux battery terminals in parallel to existing leads for plus and minus.
The DC converter is basically a small battery charger that feeds the aux battery with 13,2volts at 100mA (float charge level of battery), while your car is driving. it is important that the battery is not charged with higher voltage or current at this stage, otherwise it will cook the battery.

You may need to cut and past this url to see video

Nice info there.