How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Lou P. master tech Your Own Question
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 6656
Experience:  20 years Master Certified excellent fix rate and have access to factory wiring, and instructions.
Type Your Mercedes Question Here...
Lou P. master tech is online now
A new question is answered every 9 seconds

Mercedes mechanic.... Battery red light warning comes on

This answer was rated:

Mercedes mechanic....
JA: What is the model/year of your Mercedes?
Customer: battery red light warning comes on after 1 minute driving and no more access to other features in dash...changed main battery, changed auxiliary battery and alternator seems to work fine because wheb i turn on AC voltage is over 14
JA: Have you checked the fuses? The dashboard bulbs?
Customer: Its a 2016 GL450
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: I m trying to fix it myself
JA: Anything else you want the mechanic to know before I connect you?
Customer: Nothing else if its a fuse or relay issue maybe he can help me locate it

Hello my name is Lou.
I am going over your request now and will reply back soon with some info OR a few questions, Lou

May I have your vin number?

also do you have a mercedes scan tool to check codes?

or a meter to check the charging voltage?

Customer: replied 6 months ago.
I have the code reader device isoft but i couldnt find any code maybe you can help me with how to do it. When i turn off the engine the warning wont show up until i start and i drive for a minute then it shows up

ok, can you send me a photo of the display?

Customer: replied 6 months ago.
Customer: replied 6 months ago.

ok so if the battery is in fact charging when this message is displayed then the issue can be related to the battery sensor on the negative cable.

what needs to be done is a mercedes scanner needs hooked up so they can read the actual voltage and compare it to the voltage read with a meter.

the battery sensor has caused many issues in our cars.

I am willing to bet that is the issue,

but you need a accurate diagnoses with a scan tool

if your scan tool can read that it should be in the sam control unit

Customer: replied 5 months ago.
Ok but how can i change the battery sensor in the negative terminal. I am willing to just change it and see how it goes. Do they sell it separately ? Any advice will be much appreciated.

ok I will get you the part number

also if memory serves me on this module you need to code the new battery to the sam so it knows how to charge it


that is the part number for the sensor with the negative cable.


Customer: replied 5 months ago.
i bought it few minutes ago.
But what do you mean when you say the battery has to be coded.

you need to tell the sam module that the battery was changed.

here are the instructions you can see the last step

Customer: replied 5 months ago.
But how do i tell the sam that the battery was changed ? So bot***** *****ne could that be the problem ? And i dont need to change the sensor or i have to change the sensor most likely

you need a scanner that can perform this changing.

and i dont know about the battery sensor until we check the actual values of what the sam sees for the voltage.

i carsoft can read the info but cannot change the data so i am not sure what to tell you to do because it sounds like you want to fix it yourself but you dont have the proper equipment.

so maybe check to see if the coding of the battery helps first and then change the sensor or have the shop that codes the sam check the sensor as well or use your scanner to read the data when the fault appears on the dash.

Lou P. master tech and 4 other Mercedes Specialists are ready to help you
Customer: replied 5 months ago.
Thabks much.
One last question before i rate you.
Warning for 5 seatbelts is on.
Same car was involved in accident.
4 seatbelts was fixed by safety restore and the driver seatbelt will need replacement. After they fixed the 4 seatbelts i was hoping warning would go away for theae 4 seatbelts but they still remain on.
Will isoft get then away or how would they go away ?
All airbags have been replaced.

i need to see the codes in the icarsoft scanner for the srs airbag module

i do not believe in this rebuild service i have not seen them work so far.

but the connectors to the airbags usually need replaced after an ignition.

but yes the icarsoft can tell you the code and erase them but obviously if the code is not repaired then the fault will return.


Customer: replied 5 months ago.
Ok lastly what is the last software for the isoft ? For the GL i get the inpression i have an outdated version because the air bag code does not come up.

i dont know that info

sorry you would have to link to icarsoft and see if they can update it for you

there might be a fee i am not sure

Customer: replied 5 months ago.
Ok thanks for all.