Mystery 3 Alternators BLOWN

I have a 2004 BMW X5 ( E53 produced 1999-2006) inline 6 cylinder automatic AWD w dual sunroof (no heated seats)

Have replaced 2 Alternators in a row, they lasted about 3 days each … blown Voltage Regulators

Car History : In October replaced the spark plugs and 1 bad coil and 1 headlight bulb
Note : The inner headlights do not work
(probably needs alight control module that you have to drop the bumper to replace and costs 300 bucks
so don’t want to have to replace it unless it is causing the alternators to blow)

PROBLEM: In December replaced the battery (from Batteries Plus ) and then replaced the 140 AMP alternator
A week later replaced the 140 AMP Alternator (under warranty from OReillys) and 2 days later battery light on
Tested voltage with headlight OFF at 11.96 volts and with headlights on at 11.39 volts
SO NOW NEED 3rd Alternator ! PLEASE HELP
Note both times the iphone was plugged into the 12V outlet and noticed the close proximity of the HOT to the GROUND for the Fusible Link on the battery

I’d probably look for an Original Equipment alt.

These are OEM remanufactured … made in Mexico … installed when new from the factory

the BIMMER guys LOVE these made in Mexico FACTORY Alternators lol

Are you checking the voltage after the alternator replacement and which should be in the 13.5 volt range?

Are the blown (bad terminology IMO) alternators KNOWN to be faulty?

The odds of getting 2 bad alternators in a row are not very high IMO so this points to a diagnostic problem and/or a fault in the circuit between the alternator and battery or a power to ground fault which is causing the alternator to charge at near full bore.

When you have an issue like this, and a know other electrical problem, you cannot assume that they are not related. Your problems with the inner headlights could be causing a large load that causes the alternators to overheat.

Is the battery at a full charge prior to putting the new alternator into service?


My guess is that you have an intermittent short to ground. Since the inner headlights don’t work, you might want to start there.

Running car produces 12v so tech says alt is blown? He is saying it is not generating voltage. I took off my alt to change water pump. Put it back and did not work. Turns out the 4 pin plug on alt is touchy. I have a shim jammed into side of plug to force it sideways about .060". Alt works now.

When you had your battery replaced did they reset it? These cars will charge the battery more as it ages and when you put in a new battery you don’t want it to get over charged.

@steveng; Quote; “When you had your battery replaced did they reset it?”

News to me…what would they reset. This must be something new!!!

I have a feeling that when both alternators were installed, the battery was so drained from the previous bad alternator, that starting the car and forcing the alternator to charge the depleted battery was just too much to ask.

Charge the battery overnight and exchange the alternator for a new one the next day. Then you will be asking the new alternator to only maintain the battery.


When you change a battery in a BMW you have to register your new battery. They reset it so the computer knows not to over charge it.

@steveng: I know German manufacturers are all about “profiling” the battery so the charging rates can be customized, but isn’t a 2004 too old to have this “feature”?

That’s a good point, not sure when they started that. I have had very good luck with my BMW’s but when they go bad time to unload.

@Steveng; is this a feature that the owner can do “resetting the computer” or is this something that you will need high priced equipment to do.
I sometimes do a few repairs on a friends BMW.


Some BMW’s require the battery to be registered to the car. I don’t work on BMW’s but from what I understand if the battery is not registered many issues can result, I have also heard that there is a module that may have to be replaced after 3 battery replacements. I avoid German cars because of issues like this. Your best bet would be a well established BMW specialist or a dealer.


Registering a battery to the car? Sorry if my skepticism is showing.



He’s not making this stuff up

I don’t work on Bimmers, but I’ve heard about registering the batteries, and not on this forum

Personally, I would not replace a battery on a late model Bimmer, because I don’t have a factory level euro scan tool. If you’re not set up to do the job properly, pass on it

Anyways, this isn’t something unique to BMW

Vehicle manufacturers have recognized that it’s not necessary to go all out, charging the battery at 14.5 volts 100% percent of the time. There is logic involved, so that the alternator puts out what’s needed. No more and no less

Indirectly, I believe it’s because of emissions and fuel economy. If the alternator isn’t going full blast, there is slightly less fuel being consumed. Which means less emissions

Sorry if I didn’t explain it very well

Any theoretical fuel savings because of bunk like this has been eaten up (depending) by repeated trips to the auto parts store, the shop, and the tow trucks… :slight_smile: