Monthly Battery Drain

I dont know what else to do. My battery has been changed once every month or two for the past 4 months, because it drains completely after a few months. I cant figure the problem out. Ive had the car for two years, and this problem has just started this winter. The alternator is pretty new, and the car runs fine when jumped. If anyone can provide any help or experience with this it would be greatly appreciated.

fsu.. search it. need to do mine as well.

common e39 problem. how likely is this to be the problem?

Originally Posted by bluescholars

common e39 problem. how likely is this to be the problem?

do you poop? yep... it's that common.

Originally Posted by chivas

do you poop? yep... it's that common.

Same problem ... am hopeful the FSU I just ordered will solve this embarrassing situation ... see helpful links posted by doru

Originally Posted by bluebee

Same problem ... am hopeful the FSU I just ordered will solve this embarrassing situation ... see helpful links posted by doru

doru has posted some very good info.

A symptom of a bad FSU is that your A/C or heater fan appears to be possessed, i.e. it begins to operate (or not), at varying speeds, with no regard to the actual fan setting. And it is as common as pooping! If you remove the FSU and the problem goes away, then you have the source of your problem.

Originally Posted by Fudman

A symptom of a bad FSU is that your A/C or heater fan appears to be possessed, i.e. it begins to operate (or not), at varying speeds, with no regard to the actual fan setting. And it is as common as pooping! If you remove the FSU and the problem goes away, then you have the source of your problem.

not always. OmarMc had his go bad by draining his battery.

mine is going flat after sitting around for 5 days, not dead, just flat.

[quote=chivas;3876320]not always. OmarMc had his go bad by draining his battery.


+1. That's what happened with my car too.

Originally Posted by chivas

not always. OmarMc had his go bad by draining his battery.

mine is going flat after sitting around for 5 days, not dead, just flat.

My car is having a very similar problem, except it goes dead about every 2 weeks. My car show no signs of a bad fsu (possesed ac/heat) but are you saying that my problem could still be the fsu?

Originally Posted by amerritt74

My car is having a very similar problem, except it goes dead about every 2 weeks. My car show no signs of a bad fsu (possesed ac/heat) but are you saying that my problem could still be the fsu?

are you driving it or just letting it sit for 2 weeks?

Driving it.

Mine is showing two problems, which, after careful thinking, I think I can workaround the dead battery until my FSU arrives from UPS.

The interior A/C & heater fan was always a bit wierd. It quit on me for two weeks once, and then just came back to life on its own. It's generally a bit wheezy upon startup, for at least a half hour or so, and then goes quiet.

But, the wierdest of all is sometimes, when I shut off the engine and pull the key out, I can still hear a faint blowing of the interior motor. This sound is so faint I have to be in a quiet spot to hear it, but, I can hear it somewhere deep in the dash. I can not feel air coming out of the vents, but, I can hear the motor ever so slightly.

My workaround to the dead battery (until I get the new FSU), is to listen each time I shut down the car for this slight motor sound. When I hear that, I start up the car again and I futz with the settings on the heater or A/C. I change fan speed, automatic settings, heat settings, etc., until when I shut down the E39, I no longer hear the fan.

Generally it takes two or three tries, but, I can type like a monkey and get it to finally shut down. Then I park the car.

So far, the battery hasn't died with this workaround .... but I'm not really sure if I'm doing anything or if this is just voodoo medicine.

fsu is a common problem, but it is very possible that your car has a draw. I have an 01 e39 530 and my battery died after 2 days of not driving it (battery was depleted, wouldn't even unlock the doors.). I knew my fsu drew power intermittently because sometimes it would act strangely turning on and off. My tech friend found a draw in one of the fuses, which was the interior general computer module (controls all electronics inside your car) ($450). It sucked because i didnt have my car for a week and a half (yes it took then that long to find where the draw was coming from). The worst thing about this job is that it takes forever to find where the draw is in the car. it could be anywhere (for example, if you have two wires touching, that will create a power draw on your battery. My whole job for fsu ($100) and general module was 900 with labor since my tech friend got me a deal from his boss. Don't take it to a dealership if its not the fsu, because it will cost A LOTTT of money to find the draw if that is the case. good luck.

I have had it to a guy's shop that i know, and he said that it was my ipod dock, but i had checked that before. About a week and a half later it was starting to go dead again. I just don't want to have to take it to the stealership.

Originally Posted by amerritt74

he said that it was my ipod dock

Luckily for me, I'm replacing both my "iPod dock" (i.e., the DICE Silverline) and my FSU at the same time ... so if my monthly dead battery finally goes away ... it would have been one or the other (I hope)...

Originally Posted by bluebee

Mine is showing two problems, which, after careful thinking, I think I can workaround the dead battery until my FSU arrives from UPS.

The interior A/C & heater fan was always a bit wierd. It quit on me for two weeks once, and then just came back to life on its own. It's generally a bit wheezy upon startup, for at least a half hour or so, and then goes quiet.

But, the wierdest of all is sometimes, when I shut off the engine and pull the key out, I can still hear a faint blowing of the interior motor. This sound is so faint I have to be in a quiet spot to hear it, but, I can hear it somewhere deep in the dash. I can not feel air coming out of the vents, but, I can hear the motor ever so slightly.

My workaround to the dead battery (until I get the new FSU), is to listen each time I shut down the car for this slight motor sound. When I hear that, I start up the car again and I futz with the settings on the heater or A/C. I change fan speed, automatic settings, heat settings, etc., until when I shut down the E39, I no longer hear the fan.

Generally it takes two or three tries, but, I can type like a monkey and get it to finally shut down. Then I park the car.

So far, the battery hasn't died with this workaround .... but I'm not really sure if I'm doing anything or if this is just voodoo medicine.

Are you sure your not hearing the small fan behind the climate control unit? Its normal for that to stay on for up to 16 minutes after the car is shut down.

Originally Posted by dannyc9997

Are you sure you're not hearing the small fan behind the climate control unit? Its normal for that to stay on for up to 16 minutes after the car is shut down.

Oh. Uh?.... ... I didn't realize that. I don't even know what the "small fan behind the climate control unit" is ... uh ... um ... I don't even know what the "climate control unit" is .... (revision: Googling, I find that the CCU is the A/C-Heater control box thingey just below the radio) ...

How many temperature fans are there and which operate with no key?

1. Fan in front of radiator (I think this can stay on even if the E39 is off)?
2. Fan for blowing hot/cold air in the cabin (does normally this stay on when E39 is off?)
3. Climate control unit fan (apparently stays on 16 min even when E39 is off)

When we hear a 'fan' sound with the E39 key out of the ignition, how can we locate it to #1, #2, or #3 best?

Originally Posted by bluebee

Oh. Uh?.... ... I didn't realize that. I don't even know what the "small fan behind the climate control unit" is ... uh ... um ... I don't even know what the "climate control unit" is .... (revision: Googling, I find that the CCU is the A/C-Heater control box thingey just below the radio) ...

How many temperature fans are there and which operate with no key?

1. Fan in front of radiator (I think this can stay on even if the E39 is off)?
2. Fan for blowing hot/cold air in the cabin (does normally this stay on when E39 is off?)
3. Climate control unit fan (apparently stays on 16 min even when E39 is off)

When we hear a 'fan' sound with the E39 key out of the ignition, how can we locate it to #1, #2, or #3 best?

Donna, you should not hear #3 (sampling fan). If you can hear it, it means it is dirty. You will have to pull the whole unit out (hold in place only by pressure), and slowly dismantle it from the back. The amount of dust can be insane. Once cleaned and replaced, you should not hear any noise (very,very faint maibe). This fan works until the ECU shuts completely down (15-16 minutes after locking the car)
If that fan goes kaputt, in winter or in cold days, the warm setting will not work (a friend of mine X5 has this problem)

Originally Posted by amerritt74

Driving it.

how much are you driving?

i use to drive abotu 2 miles each way to the bridge and back for school. 2 miles is not enough to charge the battery for each start apparently so after 2 and a half weeks or so, the battery would start protesting; i wasn't driving it on the weekends either at the time.

Originally Posted by chivas

how much are you driving?

It's clearly something is draining the battery because whether or not it dies is not dependent upon the miles driven. Generally I drive only 20 miles to and 20 miles back from work; but I've been doing this ever since I got the E39 and it's working fine.

It's just that once a month, or so, the battery is so dead the lights won't even light, after leaving it overnight or during the work day. It's almost totally dead. Once I give it a quick jump, in ten seconds, it's good as new (yes, I know the battery needs to be charged for about 15 minutes on the highway).

I'm pretty sure it's something running that shouldn't be. Since the FSU is the main culprit, it's scheduled for an FSU-extraction when the new one arrives from UPS. Likewise with the DICE Silverline which is also being replaced this weekend (it's not charging my second-generation iPod touch).

If anyone has a good diagnostic procedure for which of the three fans is causing the noise after shutdown, let us know.

By this time next week, I'll have a new FSU and a new DICE Silverline so they will be eliminated as the cause of the battery drain disease.

Originally Posted by doru

Once cleaned and replaced, you should not hear any noise (very,very faint maibe). This fan works until the ECU shuts completely down (15-16 minutes after locking the car)

It would be interesting to find out typical battery-drain current figures for
1. Car turned off, but prior to the 16-minute ECU shutdown ... and ...
2. Car turned off, and after the 16-minute shutdown has occurred.

The presumption is the drain should go from a reasonable level to a much lower level after shutdown of the ECU.

1. Do we have those two drain amperage numbers?
2. What's a good way to measure this battery current drain?

Originally Posted by chivas

how much are you driving?

i use to drive abotu 2 miles each way to the bridge and back for school. 2 miles is not enough to charge the battery for each start apparently so after 2 and a half weeks or so, the battery would start protesting; i wasn't driving it on the weekends either at the time.

It is the only car i drive so... to high school, to college, then back to high school, then home, then to work, then back home or out, every day. So i drive it quite a bit. Oh ya, and it was dead today

Originally Posted by amerritt74

So i drive it quite a bit.

Me too. Today, while you guys were watching the Superbowl, I replaced my FSU in the hopes that the monthly dead battery will stop happening.

The FSU is very difficult to unclip but the rest is easy. Just one bolt, two panels, and that dastardly clip holding the FSU connector in place, and then an easy clip holding the FSU in place.

I ended up breaking the clip holding the FSU connector in place which was the only way I could get it out. Since that's OT, I'll put more details in the FSU thread but I can't see anyone ever disconnecting this just for fun.

I have the same battery drain problem and I replaced the FSU, but that did not help!
After replacing the FSU the car would not drain the battery for many month. What made me almost believe that the problem is fixed. But about a month ago it was dead again. The car usually needs to be untouched for two days until the battery might be dead. The fan also never acted up on me.
It looks like the dead battery is more likely to happen when it is really hot outside. This is probably the reason why I did not have any problems first after replacing the FSU as it was winter.
I was curious to see how big the current is that is draining the battery. On a hot afternoon I disconnected one battery terminal and feed it through a DVM back to the battery. I placed the DVM outside the trunk so I could close the lid to make the trunk light go off. After the 16min wait (for the car to sleep) the DVM measured a current of 0.9 A. In the following couple hours the outside temperature went down and the current dropped to 0.2A. I stopped the measurement here as I did not want someone to steel my DVM during the night.
What part could possibly cause this behaviour?