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Roger
Roger, BMW Master Tech
Category: BMW
Satisfied Customers: 3037
Experience:  10 yrs. experience as BMW Master Technician, shop foreman and dealer.
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Bat light came on while driving so i checked voltage at the

Customer Question

bat light came on while driving so i checked voltage at the bat. with it running. was on only 11.2 so i replaced the alternator but light still on and volt at the bat is the same
JA: Have you done a battery test? Has there been any change in headlight brightness?
Customer: no change noticed no issues with bat till this one night driving home
JA: What is the model/year of your BMW?
Customer: 1997 528i
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: told you what i did
JA: Anything else you think the mechanic should know?
Customer: after reassembly car ran rough i unpluged the mass air flow sensor and i improved
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.
Customer: it improved
Submitted: 5 months ago.
Category: BMW
Expert:  Chad Farhat replied 5 months ago.

Hi, I' m Chad. Welcome to JustAnswer. I' m reviewing your question now, and I will be post back with your reply ASAP

Expert:  Chad Farhat replied 5 months ago.

If the volts are still 11.2 we definitely not charging, we need to be 14.2 and above with all loads on .

1- was the alternator new ?

2- Can we check the battery , but under load , out of the car or you can disconnect both battery cables and test where it sits , but you need a load tester ?

3- If a alternator is good and still not charging

THEN

1- we either have a defective alternator but yours is new , unless you got a bad new one

4- the battery is not taking a charge , needs replacement if the under load test failed

5- or we missing a ground on the alternator , did you replace it yourself , can you check the ground wire on it ?

Please let me know

Thank You

Chad Farhat ( aka -Customer)

ASE Certified Tech

Customer: replied 5 months ago.
The alt only has a bat lead and a plug for the other 2 wires all on
Expert:  Chad Farhat replied 5 months ago.

it is one of 2 wires color is black ?

Customer: replied 5 months ago.
No 1 yellow 1 light blue
Expert:  Chad Farhat replied 5 months ago.

ok thats fine

hook up a test light on the positive side of battery terminal then check both wires while car running does any of them makes the test light lite up when u touch, you can back probe it by inserting test light from behind the wire thru the rear of connector ?

Expert:  Chad Farhat replied 5 months ago.

we are testing of any of these wires have ground

Customer: replied 5 months ago.
Can't test now what will the show me
Expert:  Chad Farhat replied 5 months ago.

if you getting ground , u need ground on one of these wires , if you don't have it follow the wire and see if there any break in it or touching the frame somewhere

i m assuming all fuses been checked ?

Customer: replied 5 months ago.
What fuse would affect the charging
Expert:  Chad Farhat replied 5 months ago.

Bmw online manual i have is not listing fuse labels / ID , just location

I sent you the location of fuse box in the car, just check them with a test light , should not take but few minutes , make sure all good

Expert:  Chad Farhat replied 5 months ago.

fuse box locations

Expert:  Chad Farhat replied 5 months ago.

1