Massive parasitic current leak (4 amps!)

[Multibeemer]

OK, I think I understand now. While I haven't ever re-connected my negative battery cable to its post at any time during my procedure, what I've been doing amounts to the same thing. I've been leaving the cable disconnected from its post, but then connecting a 1 ohm resistor in series between the cable and its post, and then measuring the voltage drop across the resistor. The problem has been that I had to disconnect the resistor after each test, because the current draw is so huge that it generates 16 watts (I-squared-R, where I = 4 amps, and R = 1 ohm), and the resistor is only rated at 10 watts, so if I had kept it connected long enough for everything to go to sleep, it would have burned up the resistor. This meant that I had to disconnect and re-connect the resistor every time I checked a fuse, so I inadvertently "woke up" the systems every time I tested a fuse.

So, here's what I just did:

- Removed the connectors to both of the rear hatch interior lights
- Pulled fuse 27
- Closed all the doors
- Connected the 1 ohm resistor in series between the negative battery terminal and the cable
- Measured the voltage drop across the resistor to be 0.4 volts, which equates to 400 mA
- Waited about 45 minutes
- Checked the voltage again - it had dropped to 0.038 volts, or right at the target 38 mA

So, I've established that my current drain is located somewhere in the circuits protected by fuse 27, and nowhere else (I've checked every single fuse in the vehicle, including the three that protect the blower, ruling out the FSR). Unfortunately, this one fuse, according to the label in the glove box, protects three separate circuits (glove box light, passenger compartment/trunk lights, and windshield washer system). I've ruled out the windshield washer pump by disconnecting its connector, so maybe it's one of the lights (other than the hatch lights, because I've already determined that I get the same 4+ amps flow with the hatch light connectors disconnected if I keep fuse 27 in place).

Thanks again for all the advice - I'm definitely learning a lot about how to troubleshoot this type of problem. Any tips on how to track down the actual source of the problem? I guess I'll start by disconnecting the glove box light.

[X-cellent]

I'm sure there are other things within the lighting system to check, but do all interior lights work properly when opening the respective doors? Perhaps you have a bad door switch that's causing a problem and can find it by its malfunctioning. Then i guess you need to look at how they tie into the unlock feature (I can't remember as my e53 has been gone for so long) as the lights come on with a remote unlock correct? you can do the same with glovebox switch and maybe check to see if the flashlight charger in the glovebox works properly too. Does yours have auto wipers? There might also be an issue with the windshield sensor if so....lot's to look at...electric gremlins are always the worst.

[TerminatorX5]

Check the boots covering wires going from the car to the trunk lid. Check the one on the right first. You may have a chaffed wire that either grounds or touching another wire...

[Multibeemer]

Trader4,

There's nothing fundamentally different between my methods, other than the fact that I kept the leads connected across the resistor for a much longer period of time after removing fuse 27 in the most recent test I described. So, I'm 100% convinced that the problem lies within one of the circuits that this fuse protects. It's also possible that my actual parasitic current leak is much less than 4 amps, if in fact the systems can go fully to sleep with fuse 27 in place. But that's by no means a certainty. And it's academic anyway, since I've established that when I remove fuse 27, the current drain drops to a very normal 38 mA after a few minutes. So, for the short term, I could drive the car without fear of it leaving me stranded, as long as I keep fuse 27 out, but of course that's not a solution.

X-cellent and TerminatorX5,

Thanks for the suggestions - yes, there are a lot of things to check. I believe the auto wipers are working normally, but here in drought-stricken central Texas, I haven't had much opportunity to use them in awhile. I'll start with the glove box light, since that's probably the easiest, and go from there. It probably isn't the wires going to the hatch lights, though, because when I disconnect their connectors, I still see a 4 amp draw if fuse 27 is in place.

[Multibeemer]

In response to the other thread I recently started (about the weak search feature on this site), somebody suggested a better way to search through google, so I tried it, and found a thread where someone had exactly the same problem as me, right down to fuse 27 being the culprit:

http://www.xoutpost.com/bmw-sav-foru...er-system.html

The OP of this thread ended up tracing his problem to an "LCM in the footwell". What's an LCM? Lighting Control Module maybe? And which footwell is it in? Can anyone describe what it looks like? Thanks - hopefully I'm starting to zero in on the root cause.

[TerminatorX5]

LCM is the light control module, in the passenger side footwell, attached to the right side of the car, behind carper and the plastic cover. you might not need to remove the glove box cover to get to it but the LCM is one of the very important modules in the car, controls all the lights, keeps track of the odometer mileage. the guy in the other thread had moisture problem in the LCM... you might or might not have moisture issues...

[Multibeemer]

Well, it isn't the glove box light (that would have been too easy). I found the LCM (very easy), and there's no sign of water around it. Nice and dry and clean in there, actually. So, my next step is (potentially) to disconnect the LCM, but since it controls the odometer mileage, is there any risk of getting a warning light if I disconnect it? In other words, will disconnecting it be interpreted by the system that it's been tampered with, and give a red dot which will cost a bazillion dollars at the stealer to turn off? And for that matter if it is the LCM, can I buy a used on off eBay without messing up the odometer? These things are extremely expensive new. Thanks.

[TerminatorX5]

Removing and putting back original lcm is no problem, driving without one for over 200 miles is bad for tamper dot. Getting another lcm is bad for tamper dot... take out light bulbs for trunk, see if that improves anything

[Multibeemer]

Thanks; it's a relief to know I can disconnect the LCM without generating a tamper dot. I've already tried disconnecting the hatch light connectors - no improvement. I'm thinking of doing the same with the other interior lights, but may try disconnecting the LCM first. From what I've read, I hope it's something else, as it seems like replacing an LCM is a big deal.

[Multibeemer]

Another thing to check off the list - thankfully, it isn't the LCM - I disconnected all three connectors to it, and checked the current draw after each disconnection, and got the same 4 amp current draw each time, even with all three disconnected. So I've dodged a $400 bullet.

I'm running low on things to check. I'd like to disconnect the connectors to the front and rear dome light modules, but I'm not having any luck prying the clear plastic cover piece off of the rear one. I can see a pair of indents at the ends of the long side of the clear plastic cover where it would appear you'd have to insert your screwdriver blade and pry, but it isn't coming out, and I'd hate to break it. Is there something else I have to do to get this cover off?

And any other ideas of things to look for that are protected by fuse 27?