Battery drain 740 iL - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 05-31-2011, 07:07 AM
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Battery drain 740 iL

740 il , 1998 :
Ammeter reads 12 amps drain when positioned between battery Neg terminal and Neg cable terminal.

Systematically removed fuses in trunk above battery . Still 12 amp drain.

Systematically removed engine bay fuses one by one , including the 2 fuses labelled 40 amp. Still 12 amp drain.

In doing SEARCH , I see that the front passenger seat has a fuse for power seat.
Plan to find/pull that fuse .

Anything else to consider ?
If the seat fuse removal does not isolate issue, what next ?

Any other fuses to consider?
If relays are at fault, wouldn't they be neutralized when I pulled all fuses?

What am I missing ?

Last edited by stilllearning6; 05-31-2011 at 07:08 AM. Reason: car data
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#2 (permalink) Old 05-31-2011, 03:22 PM
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Is the drain occuring without the key in the ignition?
The reason I ask is that the seat would only move with the key in and at 1st pos...
If your key is out and the drain is still there then I would suspect the battery and/or alarm etc... Stuff that doesn't require your key !!


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#3 (permalink) Old 05-31-2011, 07:36 PM
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The 12 amps battery drain occurs with the key removed from ignition and hung up inside house closet.

Can you clarify what else would drain battery ?

Is the alarm a separate circuit not passing through the E fuse box nor the trunk fuse box?

I do not know where else to explore .
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#4 (permalink) Old 06-01-2011, 05:47 AM
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Welcome to the Werkz.

Not really a definite direction, but check what happens when you disconnect the positive lead to/from the alternator. Also check if there are any Anti Pollution apparatus that could be drawing a current.
The diagnostic process you are following is sound, it's going to be something fairly large to be drawing that sort of current, so it should also be generating a fair bit of heat. I don't suppose you have any infra red camera equipment of night vision googles?


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#5 (permalink) Old 06-01-2011, 12:09 PM
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While researching other sites, I read that some folks experienced a drain attributed to the amplifier .

I am speculating that the amplifier is located in the trunk , driver side next to CD changer.
Has anyone the knowledge about the amplifier and its connections and possible battery drain ?
Is there a fuse associated with the trunk amplifier ?
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#6 (permalink) Old 06-01-2011, 02:24 PM
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Removed CD Changer and the Amplifier.
Still have 12 Amps draining thru ammeter .

Looking for sites that can drain off battery.
Seats ??
What to look for under passenger seat ?
Any pics?

I read the post about alternator positive lead , have not touched that area.
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#7 (permalink) Old 06-01-2011, 06:58 PM
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Another website advised to disconnect the engine bay positive lead from the at the engine block terminal black plastic box . The other end is attached to the alternator positive " B" terminal .
I believe that the idea was that it might be possible for the cable to have damaged insulation allowing a short to engine block ground.
My result : 12 amps still draining with the engine block positive cable disconnected and wiggled . I tried to run my hand along the entire cable length to clean / interrupt any possible short to ground . Did not solve 12amps drain .

I double checked pulling all fuses again just in case I had missed one . Still draining 12 amps.

I did a continuity check on the battery positive cable after disconnecting the positive battery terminal end and also the jumper positive terminal end in engine bay . I was hoping to find a short to ground / chassis. Showed infinite resistance , thus eliminating a shorted cable I believe.

Next step : need a listing of all relays so I can pull them . Perhaps one is shorting to ground ?? Can anyone lead me in the right direction ?
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#8 (permalink) Old 06-02-2011, 05:32 AM
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Just a stupid question, but maybe worth asking given that its a 12amp drain. You do have the multimeter on current not voltage, and do you need to change the connector that the lead plugs into on your unit? Not dissing you at all here, but I do make that style of mistake ocassionally, and then laugh at myself later.


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#9 (permalink) Old 06-02-2011, 02:05 PM
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Here's another stupid one... Does the trunk light go off when its closed ? LOL


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#10 (permalink) Old 06-03-2011, 08:16 AM
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I do not feel that any of the questions are not stupid .
I appreciate all the help.

The trunk light is out .
Re: the multimeter setting-- I have also made the setting error several times .
I will redo today to double check .

Other posts say that the amplifier and/or the radio are often the culprits.
Since both Amplifier and CD Changer are removed, I am discounting those as to possible issue.

This battery drain appeared in January and resolved itself after charging.

The trunk area that contains the CD changer and amplifier looks very clean , no water seepage detected.

Any input is appreciated.
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#11 (permalink) Old 06-03-2011, 09:47 AM
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In the rear left corner of the engine bay there is a sealed electrical box which has a lead directly from the battery, see what you can find in there.


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#12 (permalink) Old 06-03-2011, 12:21 PM
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I removed the 4 torx screws from the rear left corner of the engine bay.
It revealed 2 more fuses of 40 amps each .
Pulling those 2 fuses did not stop the battery drain.
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#13 (permalink) Old 06-05-2011, 12:59 PM
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Borrowed a better ammeter from a local guy .
Ammeter has a clamp which encircles the neg battery cable w/o requiring a disconnect -- very convenient. Digital to .00 readout.
Ammeter drains at approx 3 amps .

In past few days, kept recharging trickle charge overnight to keep battery up to voltage .

This morning it was down again even though I left the car at 4 PM yesterday with approx 00.02 amps drain . To get this low level, I had removed 2 trunk lights, 1 glove box light , trunk yellow fuse # 53 ( Rear seat adjustment , 20 amps per label on trunk battery cover ). Also, had reinstalled the Amplifier and the CD Changer . Removing them did not eliminate the drain. Also, removing
Thinking that seat motor might be an issue.

In the midst of doing isolation steps, the following has ceased to work:
both rear passenger windows: neither local door switch , nor driver master switch will power the rear windows
Central Door Lock System not function
Interior Lights , glove box light , 2 trunk lights not work

What would cause the many malfunctions?
How are these circuits related ? They appear to involve may fused circuits.
Is General Module #3 involved ?
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#14 (permalink) Old 06-06-2011, 08:15 AM
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Besides the original battery drain issue , I am now investigating the lack of functionality in :
rear power windows
central door lock
rear trunk open /close
interior lights
perhaps other systems which I do not know have failed .

The forums lead me to believe that the General Module 3 located up behind glovebox may have issues : it seems to contain several relays that control all of these functions .

Do not know how to test the functionality of the General Module 3 , nor if relays are easy to pull out and plug in a replacement .

Can anyone kindly educate me ?
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#15 (permalink) Old 06-06-2011, 03:14 PM
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You will find that all the Modules are owner-friendly and plug 'n play except for the ECU and Gearbox modules as these need matching to the car by the stealers...
Could just be a "dry connection" on one or more plugs... Give it a go mate, nothing to lose !


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