Strange intermittent electronic issues & battery draw - fixed!

[jrich4411]

I've been fighting with a couple issues in my '06 ///M roadster for a year and a half now. It started in the fall of 2012. If I let my car sit for more than 2 days I would wake up to a dead battery. I still had the OEM battery that was 6 years old by that point so I wasn't too concerned, and it was almost time to put her up for the winter anyway. So, spring 2013 I purchase a decent aftermarket battery from NAPA. All is well for a month or so & the issue returns. Bring the battery back to NAPA, they tell me it has a dead cell and give me another one. Again, a month or so goes by & I wake up to a dead battery. Again back to NAPA. This time they swap it out for one of the premium batterys.
I take the car down to my local indie who works on my domestics. He confirms that there is a 2 amp draw coming from the battery at all times, but he doesn't have the right equipment for BMWs to troubleshoot any further & recommends a German car specialist (VW's & Audi's) across town. 10 days & 3 hours of labor later all he finds is that the center console light is staying on. Well, we all learned here that issue is a broken tab or faulty switch, but the fix is simple - pull the bulb.
A couple days later I'm driving over to a friend's house when the NAV screen suddenly shuts down followed by the airbag lights (both dash & console next to shifter) illuminating. My stereo was still playing but the controls weren't working. I pulled over, restarted the car, and still no NAV, now no stereo at all & airbag lights still on. I continued on towards my friend's house & about 15 minutes later suddenly my NAV popped up, my stereo came on & the airbags went out.
I dealt with this for the rest of the year - in addition to these problems, sometimes my windows would stop working, sometimes my roof wouldn't operate, once even my wipers wouldn't work. Other times I could go a week with no issues.
I finally took the car out of winter storage about 6 weeks ago (it was a late spring here in New Hampshire). My local indie wanted one last crack at it as he had a new tech that was supposedly great at troubleshooting electronic problems. Again, he gave up.
I struggled with the decision on where to bring her - another local indie about an hour north of me who IS a BMW specialist, or the dealership an hour south. I decided on BMW.
The battery draw issue was figured out fairly quickly - it turns out my stereo wasn't going to sleep & pulling a constant 2 amps. And of course, the other intermittent issues weren't happening for them. It took them a month to get the correct stereo (4 tries) - even had one come from Germany.
after the stereo was replaced, the service writer is on the phone with me & telling me that everything is working great. He is outside, has the top down, music playing etc. Then I hear "Oh @#$@!" The top would not go back up. Finally! they duplicated the symptoms.
So, 3 more hours of diagnostic time. The end result? I have a Gap-Tech roof control module that I installed into the car shortly after I purchased it in 2009. The power to the module had been cut off previously as part of troubleshooting, but it was still connected to the ECM. Apparently it was killing some, most or all communications in the K-bus - sometimes. Very strange. So, the fix was quick, even if the troubleshooting was not!
I know this is a long post, but I hope that some time, someone doing a search on weird electronic issues is helped by my experience.

[Walkurie]

Wow. Those were some scary symptoms.

As a general rule, the electronics on these cars are pretty complex. And sensitive. When we start making any kind of mods, there is no telling what will happen. Often it is mostly a battery issue, and it can be dealt with sometimes by just a good charge. Had to trash my OEM battery in just 3 years, but the replacement is almost 5 years and still good.

However, it still has ongoing modest problems that might be related to the HVAC which I cannot diagnose. I just put up with it, as it usually just wipes out the computer memory and nothing else. Not worth the expense or stress trying to fix.