Battery drained overnight?

Tiny
BLESSING EWOBOR
  • MEMBER
  • 2014 MERCEDES BENZ GLK 350
  • V6
  • AUTOMATIC
  • 235,256 MILES
Hello, the vehicle is 2014 GLC 300. The vehicle always was noticed that the battery is been drained overnight. When the ammeter is connected in series with the battery, it was reading 12A which is very high for a vehicle that the engine is not running neither the accessories. The fuses was removed one after another to know the circuit pulling high current, none was found to pull such voltage. With all the fuses removed the reading on the ammeter was still high.
How could this diagnosis further?
Could I have the power distribution for the vehicle?

Thank you very much.
Sunday, February 9th, 2025 AT 5:05 AM

16 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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A 12 amp draw is a lot, you should be able to hear something running or a component will be hot/warm. Did you allow the modules to "sleep" before doing the testing?

Here is a guide that can help:

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

I would feel the alternator, should be cold. I would also pull fuse # 151 in the fuse panel under the hood which runs the HVAC system. Please go over this guide and get back to us.
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Sunday, February 9th, 2025 AT 5:07 PM
Tiny
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Thank you very much.

It was observed that the alternator is supplying up to 15.1V with the air conditioning running and the heads lights on.
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Friday, February 14th, 2025 AT 12:09 AM
Tiny
KEN L
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Okay, did you try removing fuse # 151 to see if the drain stopped?
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Friday, February 14th, 2025 AT 10:53 AM
Tiny
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Yes, I removed the fuse but the draining didn't stop.
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Friday, February 14th, 2025 AT 12:36 PM
Tiny
KEN L
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At a 12A draw you should hear something running or the accessory will be warm. I would start pulling up the carpet to check the modules und check for water as well. I have seen water get into the car and cause all kinds of problems. When you connect the battery do you get a large spark?
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Saturday, February 15th, 2025 AT 9:52 AM
Tiny
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Thank you, sir.
I will do as you said.
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Saturday, February 15th, 2025 AT 11:26 AM
Tiny
KEN L
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When you connect the battery do you get a large spark?
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Monday, February 17th, 2025 AT 8:39 AM
Tiny
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Yes, there is large spark.
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Monday, February 17th, 2025 AT 6:47 PM
Tiny
KEN L
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Yep, that will be a large draw. Something should be running or warm. I would check it for water damage under the carpets, this is where many modules are.
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Tuesday, February 18th, 2025 AT 9:32 AM
Tiny
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I will check and revert.
Thank you
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Tuesday, February 18th, 2025 AT 4:18 PM
Tiny
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Hello,

The following are the codes that were present when scanned.
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Wednesday, February 26th, 2025 AT 8:26 AM
Tiny
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I observed that the relay clicks sometimes even when the Engine is off, and the doors are looked. I don't know what it is controlling. Is it how it supposed to be clicking sometimes?
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Wednesday, February 26th, 2025 AT 8:35 AM
Tiny
KEN L
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With all these codes it seems like a module is not working correctly, I would clear the codes and then turn the system on without starting the engine and then run the codes again. I believe the relay is for the start stop function, does the battery draw stop when you remove the relay?
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Thursday, February 27th, 2025 AT 10:10 AM
Tiny
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I have not removed the relay. I want to know what is controlling.
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Thursday, February 27th, 2025 AT 10:53 AM
Tiny
KEN L
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Here is the layout for the fuse panel. Check out the images (below). Please let us know what happens.
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Friday, February 28th, 2025 AT 8:42 AM
Tiny
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Thank you.
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Saturday, March 1st, 2025 AT 8:46 AM

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