I am fixing up a troubled R60 S All4, so I don't have much history nor driving miles on it.

While fixing it up (turbo related stuff), I had to keep it on a trickle charger or battery would discharge to the point of no start every couple of weeks.
Now, out of nowhere, when I start the car after the battery is fully charged, I am getting discharge warning (red battery light) and fault codes for alternator mechanical malfunction and alternator electrical malfunction.
The voltage on the battery with the car idling and headlights on keeps dropping to 10V. I just shut off the engine at that point.
It has rained here heavily and I found some moisture on the alternator, which dried up, but its still giving me the same issue after full recharge of the battery.

My question: is this a slam dunk alternator replacement needed OR is it possible that a bad battery would cause charging malfunction as well?
I know that DME controls altetnator charging, so I wonder whether it's possible that a worn battery (I have no history on it) would cause DME telling alternator not to bother charging it?

i already spent a ton of money bringing this one back from dead, so I hope I don't have to replace the alternator. And I just had the front in service mode, so the thought of doing it again just wears me down!

Is it worthwhile trying a new battery first?

Thanks.

 

Yep, battery is the easy one to change. Might be a bad cell in the battery. You could have a shop load test the battery to rule it out.

 

I put in a new battery today, cleared the fault codes, started the car and the dreaded red batyery light came back on again within 30 seconds along with the same alternator faults. :(
Sounds like I cannot avoid replacing it.
I will try a used one from a local junkyard and see if that does the trick.

I'm really not looking forward to putting the front end to service mode again after putting it all back together just last week. Arrrggh.

P.S. I wish I could tell the date of the old BMW battery I took out. There is no sticker or stamp indicating its date. Sometimes it's stamped on one of the terminals, but nothing there either. 😕

 

Double and triple check all of the connections. Since you had the car in service mode, something could have easily become disconnected.

 

Good advice.
I will check, but the terminal and control plug weren't touched and both are plugged and seated. i will try removing them and replugging.Belt seems to be turning fine too.
​​​too.Also, I had the car started at least 2-3 times and running for a while without these faults as I tried to burn off the resudual oil in the exhaust.
The alternator does look covered in oil from the valve cover leak I fixed, so maybe that finished it off.
It just seemed to happened out if nowhere and I haven't even driven the car yet. 😞

 

Well, I replaced the serpentine belt and cleaned up all the oil on that side of the engine from the valve cover leak (which I replaced as well).
The belt has been changed before (NAPA belt was there), and it was in good condition.
I reset codes, started, and got the charging malfunction again. The alternator lead is sending only 5.6V to the battery at idle. So, the alternator diodes seem to be mostly gone and I have to replace it. :(
The money pit continues.

I will see if I can replace the alternator from the top without putting the front end into service mode again. I'm not sure if it's possible, but I will try.

 

Something to keep in mind is that the alternator is computer controlled. So the output may be the result of the computer telling it so. These vehicles need the new battery to be registered with the computer so the system understands how to charge.

 

That makes sense, but would the alternator behave "badly" the same way with old and new battery?

In other words, would my DME know that the battery was going bad, so it stops charging it, but instead if saying "bad battery", it says alternator electrical and mechanical malfunction?

I can register the new battery and try again, but I don't understand why a good alternator would give me fault codes about it malfunctioning. I think DME should be smarter than that if it controls the voltage signal.

 

I am having the same issue (the red battery sign/charging malfunction message) on my 2016 R60 All4S. it started with dead battery every now and then, I started putting it on a tender. Car would start and drive no issues. After a night without tender I got this message above, the car started nd died on me in 5 minutes, all the systems shutting down one after another. ... is this the alternator? May car has 160K kms on the clock, serpentine belt was replaced right before I bought it last November ... thanks in advance