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JayPutelis, Shop Foreman/ BMW Master Tech
Category: BMW
Satisfied Customers: 866
Experience:  12 yrs Experience; ASE Master Technician; ASE L1 Certified
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I have a 2010 750i. Yesterday I was driving home and I

Customer Question

Hello, I have a 2010 750i. Yesterday I was driving home and I started to get messages on my screen about my battery being discharged. The car started to shut down non essential equipment first like radio and I thought I would make it home when then the car started pop up all kind of warning messages and to shut down just about every equipment in the car like my suspension damping, steering, transmission until the car finally would not even accelerate. I was able to pull to the side of the road and turn the car off but I didn't even have enough power to turn my emergency flashers on. So basically my battery got completely drained. When I got the car home, I tested the alternator and I got 14.4V at the terminals under the hood, so if the alternator is charging why it wouldn't prevent the battery from discharging and provide the electrical power to run all the equipment in the car like it should. I don't understand. Any idea what is going on?
JA: Have you checked the fuse?
Customer: what fuse?
JA: What is the model of your '2147481646 BMW?
Customer: 2010 750i
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: yes. tested battery
JA: Anything else you think the mechanic should know?
Customer: he/she can ask me anything more
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the BMW Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: BMW
Expert:  Kevin replied 1 year ago.

Hi im kevin so can you confirm if you run car today that everything is normal?

Customer: replied 1 year ago.
ifyes everything seems normal when I start up the car. I'm just afraid to drive it because I don't know if it will die again.
Expert:  Kevin replied 1 year ago.

The only real explanation is that the alternator was not charging the battery .now its likely that the alternator is the underlying cause but until this reoccurrs its difficult to say 100% .

Customer: replied 1 year ago.
I pull the codes and found code 210901 alternator no communication and a bunch of low voltage codes. What does this code mean?
Expert:  Kevin replied 1 year ago.

This code refers to a comms issue between the engine e u and alternator does code clear down ?

Customer: replied 1 year ago.
it says that in order to clear that BSD code I have to take care of all the other BSD codes first. what does the no BSD communication fault with the alternator mean?
Expert:  Kevin replied 1 year ago.

The easiest way to explain is that your car is fitted with a smart charge type system .so the voltage can change as the battery needs more or less with the intention to inprove fuel econemy and efficiency .this means that the alternator is switched on by input signal rather than the old type of straight voltage .the car is basically saying ive asked for an increase in charge voltage but no change so a no comms code is logged as the car believes the alternator hasnt recieved this message

Customer: replied 1 year ago.
does this mean the alternator is bad?
Expert:  Kevin replied 1 year ago.

In most cases the only way to 100 % confirm would be to use an oscilloscope to check signal input from the engine control module but you would need the fault to be present at the time .

Expert:  Kevin replied 1 year ago.

Please remember to rate my service and let me know if you need anything else at all

Customer: replied 1 year ago.
i read that i could me a ground issue with the alternator BSD wire. is that possible
Expert:  Kevin replied 1 year ago.

That is possible thats why you would need to scope when fault occurrs to confirm signal

Customer: replied 1 year ago.
I can see the BSD wire plug on the alternator. how can I check the ground connection for this wire to make sure is tight
Expert:  Kevin replied 1 year ago.

I dont have a wiring diagram on your model so i cannot confirm this test .your first port of call would be to ensure the connections on alternator are clean and tight

Customer: replied 1 year ago.
that's a bummer. I expected to help me with the ground connection schematic
Expert:  Kevin replied 1 year ago.

Il opt out of the question another tech may have scematic and will be able to assist further

Expert:  JayPutelis replied 1 year ago.
Do you still need assistance? If so, can you provide the VINof the vehicle so I can pull up the wiring diagram? Thanks, Jay