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Intermittent battery draining

(2001 BMW X5)
in Kimberling City, MO on July 19, 2010
I have a 2001 BMW X5 the alternator went out had it replaced at my local shop and it was running fine then about a week later the battery died. After jumping it in ran fine for two weeks took it to the shop everything checked out. It will keep doing this. The shop has now replaced the alt 3 times and the battery twice both different brands and high end. They have checked all the fuses they are fine they have checked the alt and battery and they are fine. They have check for shorts and nothing. They even checked out the live leads when the vehicle is off and all under the amps to drain battery and all leading to radio computer etc. No after market stuff has been put on. The battery will die without warning in as little as 12 hours in the garage where we dont set the vehicle alarm but it all started after the alt was changed is there something you need to do different when you replace and alt or a battery on a BMW X5. Even the shop now is at a loss everything comes back good even the dome lights shut off automatically after the 20 min or so can someone please help us. Thank You in advance
Displaying 2 answers & 2 comments
Popular Answer
on July 20, 2010
There are two different types of alternators available for the M54 motors, a 90A or a 120A alternator. BMW can't simply look it up, the old alternator has a sticker on the housing indicating the amperage rating.

Also check to see if you have a "old style" fan speed resistor. The superseded resistor has around 40 heat sink poles, while the old one has less than half of that.
on July 20, 2010
Thank you so much i told my shop what you said a they think you nailed it because the two alts before were 90 then they went to the 120 which is on there now but getting to the point after turning the a/c or heat off the fan will kick back on for a while with the key out and it only lasts about a minute but it can be kicking on and off when nobody is in there. My only other question if you have the time is this all happened after putting the new alt on after the old one went out is it a fluke or could the new alts did this in anyway? Thanks again we appreciate it
on February 26, 2011
replace fsr /final stage resistor on for heater blower
on March 24, 2011
I hope you have fixed your X5 by now but if you haven't i might have the solution. I have also had that problem for months. Finally with the help of BMW sites and doing some troubleshooting i found it was a faulty fan speed transistor unit. My mechanics changed the Final Stage, Blower Fan and haven't had any problems.
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