Auxiliary Battery Malfunction Nightmare
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Joined: Aug 2020
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2012 ML350 Bluetec
Auxiliary Battery Malfunction Nightmare
Hi, been a long time lurker but never really posted until now to get some help. I've the Aux battery malfunction on my 2012 ML350 Bluetech with 119k miles. I inherited this car from a family member who says that this warning has been showing for several years and they never addressed it as it did not bother them. I went ahead and got a new aux battery from dealer and did the swap but the aux battery malfunction still pops up. I checked the battery and it shows about 12.6-12.7 which is where it should be. The only other thing that I could think of were the connectors which I've replaced and the message still shows up a few secs after the car is started. What am I missing here? Is there a fuse for this thing? Anyone else experience this issue?
Out Of Control!!
Joined: Sep 2018
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From: unbegrenzt
2017 GLE350 4MATIC
Hi, been a long time lurker but never really posted until now to get some help. I've the Aux battery malfunction on my 2012 ML350 Bluetech with 119k miles. I inherited this car from a family member who says that this warning has been showing for several years and they never addressed it as it did not bother them. I went ahead and got a new aux battery from dealer and did the swap but the aux battery malfunction still pops up. I checked the battery and it shows about 12.6-12.7 which is where it should be. The only other thing that I could think of were the connectors which I've replaced and the message still shows up a few secs after the car is started. What am I missing here? Is there a fuse for this thing? Anyone else experience this issue?
Thread Starter
Newbie
Joined: Aug 2020
Posts: 8
Likes: 7
2012 ML350 Bluetec
@immi08 Can you please provide more information on the connectors you replaced? Also, how old is the main battery? I would replace it, if it is older than 4 years. Less than perfect batteries and Mercedes vehicles don’t play well together.
here is the breakdown of what I did in order.
1. got new battery from dealer
2. replaced new battery and Aux malfunction light didn’t go away
3. Had dealer swap the battery thinking issue would be with battery and same outcome after 2nd new battery swap.
4. Searched forum and found out battery should be around 12.6-12.8, tested new battery and it’s at 12.7.
5. found a post suggesting issue with quick disconnect connector so replaced those and same outcome
6. here looking for help and suggestions on next steps.
Out Of Control!!
Joined: Sep 2018
Posts: 14,666
Likes: 4,568
From: unbegrenzt
2017 GLE350 4MATIC
Hi, I replaced the quick disconnect connectors that connect the wires to the Aux battery terminal. Also I did get a brand new battery and replaced it. First I thought I was given a bad battery so I had it switched out for another new battery and same issue. I couldn’t find any fuse for Aux battery either. What feature uses the Aux battery in 2012 ML Bluetec so I can make sure that the battery indeed isn’t working.
here is the breakdown of what I did in order.
1. got new battery from dealer
2. replaced new battery and Aux malfunction light didn’t go away
3. Had dealer swap the battery thinking issue would be with battery and same outcome after 2nd new battery swap.
4. Searched forum and found out battery should be around 12.6-12.8, tested new battery and it’s at 12.7.
5. found a post suggesting issue with quick disconnect connector so replaced those and same outcome
6. here looking for help and suggestions on next steps.
here is the breakdown of what I did in order.
1. got new battery from dealer
2. replaced new battery and Aux malfunction light didn’t go away
3. Had dealer swap the battery thinking issue would be with battery and same outcome after 2nd new battery swap.
4. Searched forum and found out battery should be around 12.6-12.8, tested new battery and it’s at 12.7.
5. found a post suggesting issue with quick disconnect connector so replaced those and same outcome
6. here looking for help and suggestions on next steps.
@immi08 Thanks. Can you post a photo of the quick connectors that you replaced, and describe the type of connector purchased and describe how the connectors were replaced? Thanks.
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Newbie
Joined: Aug 2020
Posts: 8
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2012 ML350 Bluetec
@immi08 Thanks. Can you post a photo of the quick connectors that you replaced, and describe the type of connector purchased and describe how the connectors were replaced? Thanks.
I used the standard quick disconnect connectors. I don’t see how they would be any different. Stripped the end/ran the wires through The connectors and crimped them down.
Out Of Control!!
Joined: Sep 2018
Posts: 14,666
Likes: 4,568
From: unbegrenzt
2017 GLE350 4MATIC
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Thread Starter
Newbie
Joined: Aug 2020
Posts: 8
Likes: 7
2012 ML350 Bluetec
@immi08 I would double and triple check the new connectors you added. Did you give a reason for needing to change them? Soldered joints are best practice for vibration-prone wiring.
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