80stech:

just went through this problem with my X. It wasn't the battery. It started after my alternator went out. Replaced it and then started having dead battery problems. thought it might be old battery so I replaced it. All good for a week. Then dead battery. Jumped it and drove for a while. All good for a week. then dead battery. Jumped it again. All good for a week. this went on for two more weeks. Then it started happening every day. All of the interim times the TCU was going to sleep, except when it wasn't. then when it kept draining the battery on a regular basis, tracked it down to the TCU.

Now, the really interesting thing. Before I started driving this car my wife's grand daughter had it in Denver. Come to find out, she had an alternator go out on her. they replaced it and then not long after that the battery kept draining. the mechanic disconnected a bunch of stuff including the TCU. After reconnecting it all was good, no more problem. Until the alternator crapped out on me above.

The poster above has disconnected and reconnected and now doesn't have a parasitic drain. Sound familiar? I suspect there is a problem with the TCU's when the alternator dies. Disconnecting the TCU seems to solve the problem.

Ok, we are missing something then, you guys should be saying that you are trying to reduce the draw BELOW 40 ma. or are you trying to find a bigger draw that you suspect is intermittent and just don't want to tell anybody ? That's a lot of posts to get where we are now.

All I'm saying is that it isn't "simple." Especially when it comes to the TCU. The problem with it doesn't seem to be consistent. difficult problem to chase.

OK, would have been nice to know more information at the start

Yes it is very difficult to pinpoint. I still do have the parasitic drain problem however. As I said at the beginning they seem to usually come down to the TCU or FSR. My vehicle does not exhibit the other symptoms of a bad FSR (surging, not shutiing down after turning off etc) so I thought I would concentrate on the TCU first. I did not not know much about that system and thus the numerous posts regarding it.

The normal mA draw the vehicle has when it finally goes to sleep exacerbates the problem because I have no abnormal circuit draw to chase. In fact fuse 74, which was looking good for 8 days, now seems like it wasn't the problem/cure. The battery was dead today and would not start. Back to square 1. Something is either slowwwwly killing it by either 'waking up' intermittently enought times to kill it slowly, or perhaps something intermittently comes on every 7 days or so that has a big draw (FSR turning on fan?) and kills it quickly then overnight? I don't know.

And from all the different threads and posts on this subject it would appear I am not alone. It seems there are many, varied causes....

Try pulling the fuses for your Nav and radio. I've been told that is another source that sometimes doesn't go to sleep.

With my radio still plugged in (30amp fuse) the car doesn't sleep. That's why I get the drain

Another thought.....
 

Another thought might be a ign s/w going bad and keeping a few things energized as the contact does not return all the way to off on some points. Would be interesting to see if wiggling the key on none shut downs changes the draw.
I have come to the conclusion that those who store for long periods of time would be better off disconnecting the battery than leaving the systems waiting for a door to open.

thanks for the latest posts - will try them all eventually! Just got back from local BMW dealership to pick up some window regulator clips and while there I was able to get ahold of the shop foreman and talk about this drain. They surprised me - he came out and talked with me for a good 30 mins even though it was fairly busy there. Excellent customer service! Not sure if that's a BMW trademark or just this local dealership but I was impressed.

At any rate he listened to all I had done so far and said I was doing all the right checks and that the first thing he was going to mention was the TCU as well. Long story short - the bottom line was he was certain that the TCU does NOTHING else on the vehicle that I personally need (ie it only does the Bluetooth stuff, cell phone, BMW Assist etc - all telephone related basically) and since I don't use that, I asked him why don't I just disconnect the dang TCU at the connector and eliminate it totally from the picture. He said they often end up doing just that and the problem goes away.

He said also that even though my HVAC isn't exhibiting any of the classic symptoms of a bad or failing FSR (surging etc) I should swap out mine as well (i picked 2 up at a U-Pull off a couple 2003 X5's).

So that's my next path. Gonna get the battery fully charged again and retested (at a different shop this time) just to make sure it is really good, then do both the TCU disconnect and FSR swap. Fingers crossed... will keep you all posted and thank you for all the help!

Of course, the cumulative effect of the battery being discharged often is that the battery life will be compromised... it may self-discharge faster than before all this, as well as deliver less short-circuit current.

Once the actual drain issue is resolved, you may well be left with a weak battery, that gives the appearance of being a drain issue! :confused: