Mystery 3 Alternators BLOWN

To me it’s just a way to get the owner away from doing even the simplest repairs in his own garage. No more helping out a sister or Mom or a good friend, and replacing their battery for them so they can save $ 50 + .


I try warning people about what can happen when power is lost to the vehicle due to a battery exchange or charging system failure.

Look at what can happen with a BMW!

This ain’t your early 90’s Toyota anymore!


Hondas use their ELD (electrical load detector) to switch the voltage on the battery between about 12.8 and 14.0 volts. When I put a plug-in voltmeter in my first Civic years ago and saw it doing this I took it to the dealer and they replaced the alternator under warranty! When the voltage boogie kept up, I found the reason and sent the dealer a write-up on it.

No BMW experience, but w/my Corolla the battery voltage (independent whether the headlights are on or not) would read between 13.5 and 14.5 volts when the engine is idling, and about 12.6 volts with the engine off & everything including the headlights off. The voltage will decrease to around 12.2-12.4 volts overnight w/the car parked.

I think you’ve got something putting a big drain on your electrical system for some unknown reason. As said above, it is very likely the headlight module, since you say your inner headlights don’t work. Your mechanic needs access to the proper test equipment to measure how much current is going in the main high current circuits. And from the alternator to the battery. With the engine running, both with lights on and lights off. If the battery is fully charged and the lights & everything (except the engine) are off the output current from the alternator shouldn’t be more than 40 amps, probably less.

I purchased an inexpensive device for this kind of measurement from Sears years ago, that’s what I use. It’s just a small meter that is deflected by the magnetic field in the wire. The more current, the higher the magnetic field strength, the bigger the needle deflection. It can measure up to 100 amps. You hold the wire in the channel of this device, and it shows how much DC current is flowing in the wire. There’s another channel if you want to only measure to 15 amps. It’s very simple, needs no batteries, I don’t think it cost more than $5-$10 at the time.

Check your battery cables. Given many manufacturers have turned to China to save a dime, many problems are associated with the lack of quality coming out of that country. The problem with Chinese battery cables is internal corrosion. You can’t see it unless you split open one or both of the cables. The amount of resistance realized as a result of this corossion is enough to make an alternator work its *ss off trying to keep up, thereby coming to an early demise.’

Thanks for all the replies !
It’s a new battery and I agree that their most likely is a short in the headlight circuit or possibly a loose connector pin
I found a used light control module and will repair the headlight circuit before doing anything else then I will check the loose connector pin and check for a bad ground between the alternator and ground will update results ASAP thanks to all ! John

Ps the battery reset is only for the newer x5s

I would still suggest that you check the voltage at the alternator and the battery while the engine is running.
If the alternator is showing 13-14 and the battery is showing 11ish then there is an issue with the circuit between the alt. and battery; possibly a failed fusible link.
If so, an alternator can fry itself while operating like this.

Steve, the reprogramming needed for BMWs is for when switching from an AGM battery to a wet cell battery. Batteries don’t come with serial numbers or microchips and they are all 12.6 volts. AGM batteries have a different charge profile.

OK4450 hey I will do that … I checked the voltage at the front of the X5 using the Hot from the battery and the frame as a ground…ang got the 11ish reading … so I can try rtesting / replacing the fusible link

I looked up the wiring diagram for the charging system for your vehicle, and there is no fusible link between the alternator and the battery.

The wiring to the battery is from the alternator, to the starter, and then to the battery.

So you might want to check those wires and connections.


@Bondito; if you checked the voltage at the positive battery post or the cable clamp…you did nothing but checked the voltage at the battery. If you have a fully charged battery and only got 11 volts, running or not , it’s time for a new battery.


I’m in agreement with Yosemite about the condition of the battery. A fully charged battery should show 12.6 volts to 12.8 volts; all depending.

@bondito, you stated earlier that you have a loose connection going to the alternator. There should be a blue wire going to it along with a green one. Both of the wires should be close to the battery voltage while the charging system is working. The blue wire is for the battery warning light and also provides power to the exciter inside the alternator. I suspect that wire has the bad connection and if so that will cause the alternator to not function if there is a bad connection on it. The green wire is for the regulator circuit. It tells the alternator if the battery requires more or less charging current.

You don’t have a short causing the trouble otherwise a fuse would blow. Another good test to make is to check the voltage difference between the alternator output lead and the positive battery post while there is a good load on the charging system. You should see less than .3 volts if the wiring is good between those points.

SILICONED the O ring and NO problems since !
Thanks for everyones help and I recommend and thanks for troubleshooting this !
Presto Auto Electric for anyone in Carson City NV area

I didn’t used to be able to afford a BMW, now that I can, they have become so complex that I no longer want one. I don’t want Idrive or touch screens of any kind to scroll through. I prefer simp;e dedicated controls that let me keep my eyes on the road. Things like needing a brand dedicated scan tool to replace a battery would make me angry enough to set fire to the thing.

So where was the antifreeze dripping that caused the alternators to blow?

Ugh… The guys are definitely on the correct path… You need to be looking at that battery HARD… BMW Alternators are usually pretty SOLID… I cringe knowing you yanked the original and used one from O’Reillys… But whatev… The guys have already led you to look beyond the alternator…and I would be doing that as well. Battery’s can kill alternators EASILY… Methinks your issue lies there…with the Batt