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I'm looking to the community to help with this one - I've searched the web for answers, and even enlisted the help (via phone) of a friend that's a BMW tech. But I can't seem to fix this problem. Seems like it shouldn't be a big deal to fix - the battery in my 2004 325ci dies when it sits - almost always if it sits for 3 days, sometimes in 2 days, and occasionally overnight. Here's the story, I'll tell all, in case there's a chance something here is a clue:

Bought the car in March of this year. No Navigation (business CD), 75k miles, leaked a little oil and apparently the sunroof leaked (noticed that AFTER I bought the car, of course), and the heated seats only work sometimes (they go on and turn themselves back off within a few seconds). When I first got it, the car would sit for a week or two at a time and always started right up. Once I noticed the roof leak, I did the following:
- pulled the seats out, front and back
- pulled up the carpet
- pulled the rear pillar covers
- pulled down the headliner a bit
- re-connected the sunroof drain hose that caused the leak
- ran a fan to dry out the carpeting, this took about a week (the padding is THICK!!)
- made the mistake of starting the car with the seats out, and the airbag light came on.
- used my Autoenginuity code reader to reset the airbag light.
- reassembled everything and all was fine
This was back in April/May. No issue with dead battery until August.

Right after that, the rearview mirror leaked. This is the auto-dimming mirror with the SOS clown nose on the bottom. I went on ebay, bought another one just like it for $30, and installed it. As luck would have it, THAT one leaked a week later. This time I bought a conventional mirror (manual tilt, NO WIRES) and put that on.

Then I changed the Vanos oil line, as that was showing evidence of leaking.

Went to the dealer and got a new key, as the car only came with one, and the remote in the original key was dead.

Those were the only jobs done on the car, then one day in August, the battery dies after the car was sitting a few days. Jumped it, started right up. Drove it, the battery charged, all seemed fine. I thought maybe the interior lights were left on. Went to use the car a couple days later, it was dead again. This repeated a few times, and I figured that maybe the battery just was shot. It looks like an original BMW battery, with some code like 27 04 on one post, so I was thinking it's probably original. So I bought a new battery, a Bosch battery that was almost $200...

But that one keeps dying too. Sometimes it'll die overnight, sometimes its fine for 2 days.

So I googled and it seems the FSR is a common point of failure for these cars. Easy and cheap enough, I bought a new FSR, OEM one not a cheap one... I removed the old one, which was original. I left the car for 7 days without an FSR installed at all. The car still would die! No sense in installing the old one as they commonly fail, I put the new one in. Still dies.

Unplugged the flashlight in case that was a problem.

Problem not yet solved, but the car was leaking oil still a bit, so I went and did the oil housing gasket job, and the belts while I was at it. Car has a clutch fan, not electric. Job done, no more leak.

OK, now for some real troubleshooting. I'm an electrical engineer, I should be able to figure this out, right??! I connected a fluke ammeter. The car pulls about 2 amps with the interior lights on, drops to about 400mA when the lights go out, then drops to 10 to 12 mA when the car goes to sleep. OK, that's well within the 36mA that I read is "normal" for these cars. I put the meter on "peak hold". It would take hours to happen, but it records spikes of 125mA. One time it recorded 250mA, and once 450mA. In the 100 times that I went to go look, it was always at 10-12mA, I never caught it with the current any higher when I walked over. I did this for 2 days, but in those 2 days the battery didn't die. so it's quite possible that whatever is killing it didn't actu up in those 2 days. I can't explain the spikes - I don't think this car has any of the modern systems where it would wake periodically to sync up with a server or anything.

OK, so I put the car back together, and remembered that when I did the roof leak fix, there were 2 modules on the rear pillars that may have gotten wet... maybe one of those is damaged. So I pulled the covers off, and unplegged them both. Looks like the one on the driver's side is for FM, AM, and remote entry antennas, and the right pillar is for the rear defroster. Well, the car died with those unplugged, too.

And that brings us to today. Car runs perfect. No check engine light. I have an advanced code reader (Autoenginuity with BMW advanced package) and it's not flagging any codes. Heated seats still don't work 95% of the time. Every once in a while it'll actually stay on. Battery still dies. Quick jump and the alternator does the rest, it's fine after running for 10 minutes.

My thoughts:
- are there any modules under the carpet, as those would be suspect from getting wet?
- any chance that REMOVING the auto-dimming mirror has anything to do with this?
- any particular circuit I should isolate (pull fuse, unplug a module, etc?
- any particular ground connections that are common to corrode, that I should go clean up?
- could it be that the new battery is just plain defective?

I'll try anything at this point. My wife wants me to bring it to BMW, but I'm afraid of getting a $2000 repair bill for all the time troubleshooting, for a car that cost me $4000...
 

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OK, now for some real troubleshooting. I'm an electrical engineer, I should be able to figure this out, right??! I connected a fluke ammeter. The car pulls about 2 amps with the interior lights on, drops to about 400mA when the lights go out, then drops to 10 to 12 mA when the car goes to sleep. OK, that's well within the 36mA that I read is "normal" for these cars. I put the meter on "peak hold". It would take hours to happen, but it records spikes of 125mA. One time it recorded 250mA, and once 450mA. In the 100 times that I went to go look, it was always at 10-12mA, I never caught it with the current any higher when I walked over. I did this for 2 days, but in those 2 days the battery didn't die. so it's quite possible that whatever is killing it didn't actu up in those 2 days. I can't explain the spikes - I don't think this car has any of the modern systems where it would wake periodically to sync up with a server or anything..
See? It just needs a little caring :)

You measured the current on the battery negative terminal, right?

I would just keep going with these measurements, takes a lot of time but bulletproof.
Just create a tree of supply voltages based on the wiring diagram and follow the branches.
http://www.bmw-planet.net/diagrams/release/en/

Other than checking under every carpet for water leaks I would suspect the trunk lid cabling at the right hinge.
 

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- are there any modules under the carpet, as those would be suspect from getting wet?

check the walls under the A pillars in the front footwell for water

- any chance that REMOVING the auto-dimming mirror has anything to do with this?

no

- could it be that the new battery is just plain defective?

i don't think so
 

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There are no electrical components under the carpet. No, the swap out of the mirror won't cause this problem. Likely the final stage resistor is bad. It's a common issue.
 

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If you find out please let me know too. My car has the same issue. I go thru a battery a year and its about the same time as the fall season starts. If the car sits for more than 2 days the battery is wasted. As long as I drive it everyday its fine. I have 4 cars so I dont drive mine everyday. I just keep the negative off the battery for now until I drive it. I want to find out the problem.
 

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To diagnose a parasitic electrical power drain you need a digital volt/ohm/current meter.
- disconnect the ground/earth/negative cable from the battery
- set up the meter to read current (amps)
- connect one meter lead to the battery post
- connect the other lead to the ground cable
- allow the car to go to sleep (~15 minutes)
- read the meter

Anything over 80 milliamps (80ma; 0.08 amps) is too high. My 2001 330Ci reads about 55ma. The first suspect is the final stage resistor (FSR). The FSR is a cluster of resistors that the climate control uses to provide different fan speeds. I'm talking about the fan for the interior heating and AC! They go bad. The FSR is located in the dash on the passenger side (LHD) of the dash. Check YouTube for vids.

If the FSR is ok the next step is to start pulling fuses one at a time. That is, check fuse map and pull an individual fuse to see if the meter reading drops. If it doesn't drop reinsert the fuse into its proper slot and move to the next one.

Happy hunting.
 
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