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Battery Drain - An interesting one...


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I have an interesting battery drain. I noticed that when I leave my car stationary for two weeks, it's enough to drain the battery. I Installed a CTEK Battery health indicator and noticed that it's rarely ever green.


For those of you interested: the Ctek Health Indicator uses 2 mA.So today I started my investigation with a multimeter. I pulled all lamps (trunk, glove box, left and right door and made sure no other lights are on and waited till the speedo was off.


B1 pulled 167mA (Cluster Tiptronic, Diganosis and Power Top)

C3 pulled 123mA (CU Alarm System, Central Locking, Power Window)

D1 pulled 103mA (Power Window)

D8 pulled ended at 100mA (Radiator Fan 2)


So even after all fuses pulled I have still double the standby current left that it should have. At this point I have no idea where to look for as I have no accessory installed that are not going through the fuse box. The different accessories I have all end up in one fuse that I take power from (seat fuse).

Do you guys have any idea what I could try next?



Edited by fedmax
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The car should have a normal draw in the 40-60 mA range when the car is fully powered down (everything off, then wait about 5 min. or so), anything beyond that is a problem. I would start looking for any aftermarket installs (radar detector, phone charger, iPod, etc.) that is connected to an "always hot" circuit like the cig lighter. We recently had a similar problem car in the shop, and found two small electronic device chargers hardwired into the system buried up under the dash by a previous owner; as soon as they were removed, the car showed a normal draw.

If you do not find any aftermarket devices, you then need to start checking the OEM stuff one at a time as they sometimes also can crap out and start an unexpected drain.

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Thanks JFP, I know the car quite well because I took a lot of it apart the last two years. All aftermarket stuff I did myself and that is wired to the fuse box, so...I have the work ahead that I don't want at the moment :-( So bring it to the shop most likely.

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You need to wait much longer before measuring the drain, and you need to do it with the car locked. Use a screwdriver to latch the front lid, so you can leave it open while you do the test.

attachicon.gifload drain table.jpg

Thanks Richard - very good list. But still my question: with all these fuses pulled (relating to all these consumtions listed in the document) what is still draining the battery i.e. which parts are not controlled in that fuse box?

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There are several timers which cut out after locking the car at vaious intervals. For example, the DME holds power onto the oxygen sensors for about 15 minutes. I guess you could pull the DME fuse to eliminate that one.

Was the car locked when you did the test? As the load table shows, you need to lock the car and wait 61 minutes before all the timers time out, and measure the drain at that point.

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If you have little or no results with the advice already given by several members of the board, disconnect the alternator as well and check again, often it's in the diode bridge of the alternator, a loss of 0,1 Amps. is much with an empty fuse box.

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If you have little or no results with the advice already given by several members of the board, disconnect the alternator as well and check again, often it's in the diode bridge of the alternator, a loss of 0,1 Amps. is much with an empty fuse box.

Interesting, I was just thinking the same thing...................

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