W166 Battery Discharge Issue
Thread Starter
Newbie
Joined: Jul 2022
Posts: 8
Likes: 3
2014 ML350
W166 Battery Discharge Issue
Hi everyone,
I'm brand new here and hope have searched older threads without luck. I have a 2014 Ml350 BT. Couple weeks ago, the red battery alarm came up on the dash. I measure on the battery and boosting posts while idling and saw that there didnt seem to be a charge coming from the alternator. I had the alternator replaced but still have the same issue. Further investigation using the Dyno menu, i found:
UB : 11.5 - 12.2 on idle and car off, increases when to various values and max is around 14.6V
IB: -8A when off, -30A when idling, goes to various positive values while driving but returns to a negative value when I stop.
I have also swapped the big battery under the seat and have the same scenario.
Any ideas or assistance on what could be causing this?
Thanks
Avi
I'm brand new here and hope have searched older threads without luck. I have a 2014 Ml350 BT. Couple weeks ago, the red battery alarm came up on the dash. I measure on the battery and boosting posts while idling and saw that there didnt seem to be a charge coming from the alternator. I had the alternator replaced but still have the same issue. Further investigation using the Dyno menu, i found:
UB : 11.5 - 12.2 on idle and car off, increases when to various values and max is around 14.6V
IB: -8A when off, -30A when idling, goes to various positive values while driving but returns to a negative value when I stop.
I have also swapped the big battery under the seat and have the same scenario.
Any ideas or assistance on what could be causing this?
Thanks
Avi
MBWorld Fanatic!
Joined: May 2021
Posts: 2,524
Likes: 2,041
From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
Get a scanner to pull out some DTC, likely a damaged alternator or voltage regulator (mounted on the alternator), but the codes before changing any other components. Diagnosing the source will save you $$ and frustrations
The voltage on the cluster should be @14.2 on idle.
The voltage on the cluster should be @14.2 on idle.
Thread Starter
Newbie
Joined: Jul 2022
Posts: 8
Likes: 3
2014 ML350
Would a faulty aux battery cause such a drain? I measured it as i was able to reach the + terminal. Measured 12.5V. Just wondering if maybe it has a current load issue and is therefore pushing load to the main battery.
I'm most probably going to get a scan done tomorrow and will share the findings.
Thanks
I'm most probably going to get a scan done tomorrow and will share the findings.
Thanks
Out Of Control!!
Joined: Sep 2018
Posts: 14,666
Likes: 4,568
From: unbegrenzt
2017 GLE350 4MATIC
An 8 (or 9 depending on build date) year old car should be on its third batteries at this point. If the batteries are over 4 years old, change both the main and aux. And read codes.
Thread Starter
Newbie
Joined: Jul 2022
Posts: 8
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2014 ML350
Update: Had the scan done at a dealer. While most systems complain about low power supply, the stand out error is "The alternator has a malfunction. There is an open circuit" Fault code : P065B13
I will have to take it back to the mechanic that did the alternator repair and take it from there.
I will have to take it back to the mechanic that did the alternator repair and take it from there.
Thread Starter
Newbie
Joined: Jul 2022
Posts: 8
Likes: 3
2014 ML350
Update: Had the scan done at a dealer. While most systems complain about low power supply, the stand out error is "The alternator has a malfunction. There is an open circuit" Fault code : P065B13
I will have to take it back to the mechanic that did the alternator repair and take it from there.
I will have to take it back to the mechanic that did the alternator repair and take it from there.
So after attempting to have my alternator properly repaired got me frustrated due to lack of spares locally, I eventually had to settle for a used part that came of an accident damaged vehicle. Had it changed and all is well. Display on cluster showing a consistent +14V and current on idle is around 8.5 A.
Now back to my next big issue... oil cooler leak
Thanks again!
MBWorld Fanatic!
Joined: May 2021
Posts: 2,524
Likes: 2,041
From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
Glad to hear you got it working again 
. Nothing wrong with an adopted part. You are giving it a new home, and longer life to it.
Since your alternator already failed, I would try getting your original fixed over time (no rush) and have it as a spare
. Nothing wrong with an adopted part. You are giving it a new home, and longer life to it.Since your alternator already failed, I would try getting your original fixed over time (no rush) and have it as a spare
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Out Of Control!!
Joined: Apr 2019
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
good & bad charging... all at the same time!
The one thing to keep in mind is the dynamic voltage is ECU CONTROLLED... and may go bad after extended driving period.
So drive with the instrument cluster showing your battery vitals is a pretty safe practice.
The ALT itself is 100% okay... it's the controlling ECU that is amazing 🙄
Do not assume a good charging system now is going to keep working well after 50mn... It may go nuts and drain battery below 12V without any CEL warning light, no DTC code, nothing !
In a pinch, restarting the vehicle should temporarily clears that issue to get back on the road.
Last edited by CaliBenzDriver; Jun 7, 2023 at 08:53 PM.
