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CarDoc, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 631
Experience:  IMI L3 Motor Vehicle Mechanic
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Fault related to the fact that my battery (new) keeps going

Customer Question

Fault related to the fact that my battery (new) keeps going flat, plus have an intermittent problem related to the radio/sat nav/ cd unit all on an ML Mercedes can you help?
JA: Have you tested the battery with a voltmeter? And can you see if it's leaking or not?
Customer: The Batt is Brand New for a Mercedes-Benz
JA: What is the model/year of your Mercedes?
Customer: 2007/8 ML 320 Cdi 4 Matic
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: No, apart from buying the new Batt at £175.00
JA: Anything else you want the Mechanic to know before I connect you?
Customer: Just sort the radio and the drain on the batt
Submitted: 18 days ago.
Category: Mercedes
Expert:  CarDoc replied 18 days ago.

Hi, How are you?
I'm Shabaz, one of the automotive experts, I'm sorry you're experiencing problems with your car, I will do my best to help you today.

Firstly, what is the issue with the multimedia system? This could well be the cause of the battery drain issue.

Customer: replied 18 days ago.
I can activate the system, the merc logo appears then after a couple of seconds disappears. Very occasionally the radio will without any prompting come to life, and will continue until I switch off the ignition and will not operate again, then out of the blue it springs into life.
Why I have not a clue?
The battery which is brand new goes flat if the car is not used on a daily basis or just for short journeys. Would be grateful if you could spread some light on the matter
VBR Eric
Customer: replied 18 days ago.
Looking forward to some input!
Expert:  CarDoc replied 18 days ago.

Sorry I am unable to take calls at the moment.

Have you tried to hard reset the multimedia system by pulling the fuse?

Customer: replied 18 days ago.
No And I would not know where the fuse is located, maybe you can direct me.
Expert:  CarDoc replied 18 days ago.

Fuse number 25 in the fusebox located in the boot is for the multimedia unit. Switch the car off, pull the fuse, turn the ignition on to verify that there is no power. Leave it for about 5 minutes and refit the fuse.

If you have a diagram on the inside of the the fusebox cover or in your manual, I would recommend referring to that, you're looking for COMMAND operating, display and control unit.

Let me know the results and I will also explain how the battery drain problem needs to be checked.

Customer: replied 18 days ago.
Hi, I did as instructed but it didn’t make any difference.
Where are you located and maybe I could bring the car to you ?
Expert:  CarDoc replied 18 days ago.

I am in the north of england. I actually work for a dealer and not my own garage. I would recommend finding an independant garage who focuses on diagnostics because your car needs to undergo a parasitic drain test as well as troubleshoot the multimedia system.

The logo turning on and off means that there is a problem with a component on the multimedia system which is connected via fibre optics. When the MB logo comes up, the head unit is doing a system check and if there is something wrong, the head unit turns off.

You can buy a fibre optic loop which you use to bypass each component connected via fibre optics; cd changer, navigation, voice control module etc.

The fibre optic cable is a twin orange cable that plugs into each component (it's easily visible), you unplug this, connect the loop and switch screen on to see if it boots up, you do this process for each component until the head unit loads up.

I hope you understand what I mean.

Expert:  CarDoc replied 18 days ago.

This image shows a simple male and female plug fibre optic loop.