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Possible battery drain issue?

Tiny
BHAMDOC1973
  • MEMBER
  • 2010 MERCEDES BENZ ML350
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 133,000 MILES
My uncle has had this car for years. I installed a new battery for him when I bought it for him 5 years ago. One day 2 weeks ago it would not start so my cousin checked the battery and found it dead. Bought another, not an AGM and installed it. 5 months later the same thing happened, he said. He trickle charged it and it started so he replaced it under warranty. Doing the same thing. He believes it may have a parasite drain. It will start now. How can I tell if it has an initial drain first before digging into pulling fusee. Can I do some type of voltage test on the battery while it's off to see first if anything is pulling current?
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Wednesday, January 8th, 2025 AT 11:36 AM

20 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,983 POSTS
Hi,

If the vehicle calls for an AGM, that is what you should be using. They have a longer lifespan, are more resistant to vibration and shock, recharge faster, and produce less gas. These vehicles place a heavy load on the electrical system and often, a traditional lead acid battery won't keep up.

Now, you could check to make sure the alternator is doing its job. That is where I would start. It may not be keeping up.

Here is a link that explains how to check it. It's very easy.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Also, make sure there are no lights in the trunk, glove box, or other hidden ones that may be staying on. If it has a CD player, remove the CDs to make sure the unit isn't staying on.

Take a look through this link:

https://www.2carpros.com/articles/car-battery-dead-overnight

Let me know if that helps or if you have other questions.

Joe
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Wednesday, January 8th, 2025 AT 7:37 PM
Tiny
BHAMDOC1973
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Definitely not the battery or a drain or an alternator issue. Symptoms are in line with the ISM module on these. But hard to know for sure, but that's what it seems like. I went to start it again and got nothing. Codes are attached. Delete them and I get some back. Am almost sure it's not the ignition itself.
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Thursday, January 9th, 2025 AT 12:51 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

It could be the ISM, but it could be an open in the can-bus. No signal is usually the result of a breakdown in continuity (broken wire, connector pin, corrosion). Have you been able to inspect any of the CAN wiring or connections?

Joe
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Thursday, January 9th, 2025 AT 7:09 PM
Tiny
BHAMDOC1973
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No.
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Thursday, January 9th, 2025 AT 7:35 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,983 POSTS
I suggest you do what you originally asked, check for a draw.

To do that, disconnect the negative battery terminal. Connect a multimeter between the neg cable and the neg battery post.

Allow the vehicle to sit for a few minutes and ensure everything electrical is off and the key is not in the vehicle. Have the multimeter set to Milliamps. You shouldn't see much more than a 50-milliamp draw with everything off. Anything beyond that amount will likely cause the battery to fail.

Let me know what you find.

Joe
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Friday, January 10th, 2025 AT 7:27 PM
Tiny
BHAMDOC1973
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Yes, that is the procedure I was asking about, thanks. I will do it regardless, but I am sure it's not a battery issue as it's showing 12.2 off and 14.5 running when I received it. Next day when to scan it and volts while off was 12.2.
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Saturday, January 11th, 2025 AT 5:52 AM
Tiny
BHAMDOC1973
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I assume my settings are right like the picture. Between yesterday and today everything was dead when I went to start it but in doubt it's a draw, I put a jump box and it started fine without struggle, left it on without the box for 7-8 minutes, turned it off and on and it's strong. Checked voltage of battery and alternator and its charging 13.5. I don't see any numbers as far as a draw. Is this correct set up? Shows zero.
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Saturday, January 11th, 2025 AT 9:39 AM
Tiny
BHAMDOC1973
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Also checked codes again and it started several times no issues, but once or twice did the same where it won't go into drive or reverse initially that's why am thinking the ISM. Also, when you say test with the multimeter and make sure everything is off, well, the battery negative is disconnected so everything must be off. Also, these cars have a smaller battery next to the big battery, it's also new.
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Saturday, January 11th, 2025 AT 9:57 AM
Tiny
BHAMDOC1973
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Also have not yet gotten to the ISM to look at it but they are sold programmed for 200 so I may get one. But I noticed a small transmission leak. I am now thinking it maybe possible that it's also low on fluid and I know these would start having these issues where it won't even go into gear if it is or go into gear and goes back to park. But I doubt it here as the issue is that you won't even see it go to drive or reverse, won't make a sound and indicator won't move from park.
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Saturday, January 11th, 2025 AT 10:00 AM
Tiny
BHAMDOC1973
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Even with this other one same thing zero.
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Saturday, January 11th, 2025 AT 10:40 AM
Tiny
BHAMDOC1973
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Also noticed a bit of water residue under the fuse box in the back. Not sure if all these issues are related. Also dash says brake lamps are burned or whatever but they all work.
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Saturday, January 11th, 2025 AT 11:37 AM
Tiny
BHAMDOC1973
  • MEMBER
  • 1,719 POSTS
I think when I come back the next day to check it's not that the battery is dead but that power is post to the battery, that's why everything is dead. Next day when it's all dead I will measure battery and see if it's still full. But I'm not sure what feeds the power.
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Saturday, January 11th, 2025 AT 11:38 AM
Tiny
BHAMDOC1973
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I got something, not sure if this is 2 amps or what, but it's between 2.6-3. Whenever I touch the negative post I get noise from the cd changer and something else in the back. But it feels pike a magnet and that if I continue touching it that it may burn the multimeter.
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Saturday, January 11th, 2025 AT 12:28 PM
Tiny
BHAMDOC1973
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The noises I am hearing are from the cluster, it lights up part of it, and the rear gate switch, I think. All that when touching the negative post. Also removed the CD from cd player in case as I thought I heard it too.
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Saturday, January 11th, 2025 AT 12:35 PM
Tiny
BHAMDOC1973
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I found something making a noise under the hood and continued for a while, turned out the auxiliary water pump. Car isn't hot so I'm not sure why the small pump is running after. Unplugged it for now to see if it's what's causing the battery issue. Also deleted the ton of codes in front and rear sam. Also, found this code about the rear gate. Deleted it and now the gate works. No codes came back so far for anything.
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Saturday, January 11th, 2025 AT 1:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,983 POSTS
If the pump continues to run, it will drain the battery. The pump is actuated by a relay (see picture below). Switch it with a different one with the same part number to see if it stops the pump.

Let me know.

Joe

See pic below.
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Monday, January 13th, 2025 AT 5:26 PM
Tiny
BHAMDOC1973
  • MEMBER
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Turned out these run 30 minutes after the car is off if you select AC REST to keep the temp inside as chosen. Turned that option off and it's no longer on. The only thing I did was delete all the codes that were there, and the car is fine. The only thing I had that wasn't working was the back gate it would open but not close t had a code for the anti-pinch strip on one side. I think water getting in from the taillight seals caused some moisture, since it's been in the garage a week and dry, no issues so far.
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Monday, January 13th, 2025 AT 5:39 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,969 POSTS
Yep, I was going to say I would check for a stuck CD in the player. Also, the Electronic Stability Program (ESP) module seems like it is not working are there is a problem with it. Please check for water under the carpet. You might need to remove the seats, there are many modules under that if they get wet, they will stop communicating and have a battery draw. Check out the images (below). Please let us know what happens.
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Thursday, January 16th, 2025 AT 8:44 AM
Tiny
BHAMDOC1
  • MEMBER
  • 86 POSTS
Yes, I am familiar with water under the seats and on floor on these cars but none, only traces are by the rear fuse box. I let it dry for days inside the garage and all is good now. The rear sam on these is under the rear seat so that's good. I ordered the tail lamp seal to replace it. But most likely water in the rear got some moisture in the rear fuse box. No codes have come back at all so far.
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Thursday, January 16th, 2025 AT 9:21 AM
Tiny
KEN L
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Nice work, let me know if you need me for any other issues.
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Friday, January 17th, 2025 AT 11:35 AM

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