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battery drain - life span of an fsu?

4122 Views 12 Replies 8 Participants Last post by  skeggy
since we had the snow here in the uk i havent used my car for about 2 weeks, when i can to do so the battery was flat and had to just start it. took it for a long drive to charge it back up, next day car was fine. havent used car for 3 days and car is dead again (getting click click)

New Battery 12 months ago and Fsu was replaced 16 months - is there a likely hood the fsu is playing up again? what are peoples experiences with having to change them?

Ive read the other threads on battery drains - got to get myself a multi meter to check currents, but dont leave phone plugged in, etc
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same thing happen to me... i replaced battery, then fsu and battery...still looking for the cause, i use the car everyday, so no time to see what happens after 3 days of sitting, curious to know what your issue is.
I replaced the FSU twice in the past 55k miles on my '02.
It's quite possible to the FSU to go bad within a year! However, check for other common causes of current drain :

- The Phone TCU module, not the phone itself, this is the control box in the boot.
- The Traffic Master system in UK spec cars, again the module in the boot.
- The Nav computer not powering down, this can be caused by a dirty or scratched map disk.
- Third party iBus devices, iPod interfaces, StealthOne etc. If these do not go to sleep correctly they keep the entire car awake.

It's quite hard to check the current draw on the E39 as when the boot is open the car will not fully go to sleep for about 15 minutes. You must leave the boot open with the ammeter connected up, then wait until the boot light goes out. Now check the current reading, it should be significantly less than 100mA, usually about 10mA. You'll need an ammeter that will take at least 10A as that will be the draw when you first connect it up, unless you can manage to connect the meter without breaking the circuit this can be done if you are careful or with a clamp meter.
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I have a similar issue, flat battery after two weeks of snow covering the car. Absolutely no life at all, no dash lights, absolutely sod all. Plan is to change FSU as a matter of course, and follow threads detailing removal/disconnection of TrafficMaster, and see how it goes from there. Reason for is FSU is I suspect it to be iffy, while driving along, I can suddenly get a massive blast of red hot air through the vents for seemingly no particular reason. Will never use the TrafficMaster and I understand it can cause problems by just being there. Had issues with screen on Nav turning itself off during the Xmas season, so want it out in case it's causing issues now.
ive only covered 10k with the new FSU - no other devices plugged in - but will check the phone, tm and nav system
Si, as said above the TM system can and does play havoc regarding current drains.

Mines ok at the minute but when the weather gets a bit better it will be going in the bin thats for certain
blonde moment - is the fsu under the drivers side or passengers side of uk cars? anyone got any idiot proof links?
sorry it was late / early and got 2 different guides from the search which then frazzled my brain! LOL

Change the FSU today and so far so good. Car is, as was always running at 13.2v-13.7v on running and with ignition off 11.4v-11.6v

so to clarify looks like an fsu can only last 14 months and less than 10k.
Have you thought about a trickle charger. My previous owner was kind enough to include a BMW trickle charger with the car.
I make sure to hook the charger up via cig lighter anytime the car will be sitting for more than a couple of days
i thought that i had one - but on more investigation it appears that its not way near powerful enough to keep the battery topped up. What size / power is yours?
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