I purchased the car a year ago. About 5 months ago got intermittent alternator light on - early in day, typically when car had been idle for a number of hours, and often with the A/C on. I’ve had the alternator replaced, Battery replaced. Still continued with the problem. I then had the headlamp indicator come on intermittently, with but not at the same time as the alternator indicator. At times, neither would be on. We checked and proper voltage at the battery when the car is running. I’ve had a brake switch replaced (computer code repeated error), and had the igniter replaced in one of the xenon headlight where the indicator lamp said i had a bad bulb. Since the ignitor replaced, no failed light indicator, but the alternator light still comes on. I’m very frustrated, not to mention spending too much money to attempt to fix what very much feels like a short. Any ideas?
Don’t know much about BMW, but the drive belt could cause the problem. I had a similar problem with the wife’s Windstar and it turned out to be the water pump that was binding up. Could no find that one until the blasted thing started running hot.
Very intermittent failures eventually becoming more frequent is a fairly common mode of alternator failure, so it could just be an alternator that’s on it’s way out. The lighting issue is probably just a coincidence.