Battery drained overnight?

2014 MERCEDES BENZ GLK 350

235,256 MILES • V6 • AUTOMATIC

BLESSING EWOBOR

MEMBER
754 POSTS
FOLLOW

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.

Feb 9, 2025 at 5:05 AM

STRAILER

CERTIFIED EXPERT
53,872 POSTS

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.

Feb 9, 2025 at 5:07 PM

BLESSING EWOBOR

MEMBER
754 POSTS

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.

Feb 14, 2025 at 12:09 AM

STRAILER

CERTIFIED EXPERT
53,872 POSTS

Okay, did you try removing fuse # 151 to see if the drain stopped?

Feb 14, 2025 at 10:53 AM

BLESSING EWOBOR

MEMBER
754 POSTS

Yes, I removed the fuse but the draining didn't stop.

Feb 14, 2025 at 12:36 PM

STRAILER

CERTIFIED EXPERT
53,872 POSTS

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?

Feb 15, 2025 at 9:52 AM

BLESSING EWOBOR

MEMBER
754 POSTS

Thank you, sir.
I will do as you said.

Feb 15, 2025 at 11:26 AM

STRAILER

CERTIFIED EXPERT
53,872 POSTS

When you connect the battery do you get a large spark?

Feb 17, 2025 at 8:39 AM

BLESSING EWOBOR

MEMBER
754 POSTS

Yes, there is large spark.

Feb 17, 2025 at 6:47 PM

STRAILER

CERTIFIED EXPERT
53,872 POSTS

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.

Feb 18, 2025 at 9:32 AM

BLESSING EWOBOR

MEMBER
754 POSTS

I will check and revert.
Thank you

Feb 18, 2025 at 4:18 PM

BLESSING EWOBOR

MEMBER
754 POSTS

Hello,

The following are the codes that were present when scanned.

Images (Click to enlarge)

Feb 26, 2025 at 8:26 AM

BLESSING EWOBOR

MEMBER
754 POSTS

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?

Image (Click to enlarge)

Feb 26, 2025 at 8:35 AM

STRAILER

CERTIFIED EXPERT
53,872 POSTS

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?

Feb 27, 2025 at 10:10 AM

BLESSING EWOBOR