Battery drain 1999 740i

**MrChrysler** · 01-17-2016, 06:40 AM

I got 1999 740i with current drain which is killing my battery. Previous owner has installed a switch on the ground cable because he had the same issue, he could never fix it, and that allowed him to switch off the car after each journey. After 16min the current leakage drops to approximately 0.34A and it stay like that for hours. Ammeter was connected between ground cable and ground on the battery for a test.

At once I have removed all Fuses in the glove box, all fuses in the box underneath the steering wheel, all fuses + 2 relays which were in the trunk where the battery is. The battery drainage did not change significantly only by 0.01A.
Then, underneath the bonnet I have unplugged ABS/DSC module, then DME + 2 other ECUs which are located "under window" on the passenger side, in the same place underneath the ECUs I have found some relays which I have also disconnected. Then I have disconnected the phone, and then I gave up.

Can someone tell me what else is left for me to check that is not protected with a fuse and could cause the problem?

Rain sensor? Is alarm unit fused in the trunk? Gearbox?

**xlr8tin** · 01-17-2016, 08:44 AM

This is a great question...Both 740's I've had did this. I learned that it was whenever I tried to lock it with the key fob. So I stopped using it and put the key in the door everytime. I haven't had the issue since. I think it has something to do with the EWS

**MrChrysler** · 01-17-2016, 11:53 AM

Do you remember how many amps did your cars drained? was it similar to my value of 0.34A? Did you do anything to try to fix it?

**Mayorchuck** · 01-17-2016, 01:04 PM

If it's .34A and not .34mA, you have quite a drain.

Edit: I would check the second info first.

I would suggest pulling the RH seat, drivers seat for you, passenger in US. You will find this:

F107, X13030

inside RH frame side member

F107	Fuse F107
X13030	Cable shoe Output, fuse F107

That is fed from the Fuse 100

F100, X819

in rear RH side of luggage compartment

F100	Fuse F100
X819	Cable shoe B+ supply fuse carrier, luggage compartment

These are fuses 100 to 106. If it drops by removing Fuse 100, I would then move on to the fuse block under the seat. Each of these lead to a large group of blade fuses.

**MrChrysler** · 01-17-2016, 04:51 PM

I didnt know that there are more fuses in the car, I only knew about the fuses with "pretty colours", how many is there?

**Mayorchuck** · 01-17-2016, 05:07 PM

Those should be the only ones you had not checked. The ones under the seat are often a victim to water from sunroof drains leaking.

It should look like this:

**MrChrysler** · 01-17-2016, 05:51 PM

If those fail, are there any replacement fuses available? Is it under the carpet?

**Timm** · 01-17-2016, 06:00 PM

Don't forget the alternator - that is often the source of large drains - you would need to remove the B+ cable - but this must be done with the battery disconnected, just too dangerous to do it live. Also - something I came across recently was a method that BMW use to trace current drain WTHOUT removing the fuses:

http://www.meeknet.co.uk//E64/Fuse%2...20Readings.pdf

**psjr** · 01-18-2016, 01:16 AM

Originally Posted by Timm

Don't forget the alternator - that is often the source of large drains - you would need to remove the B+ cable - but this must be done with the battery disconnected, just too dangerous to do it live. Also - something I came across recently was a method that BMW use to trace current drain WTHOUT removing the fuses:

http://www.meeknet.co.uk//E64/Fuse%2...20Readings.pdf

That is very neat, thanks!

Replacement fuses should be basically free since there are tons on any parts car. But usually the wiring/connectors not the fuses that go bad.

**MrChrysler** · 02-07-2016, 12:24 PM

I found the problem. It seems like F103 is draining power. 4th from the left side...

What is it?

**Mayorchuck** · 02-07-2016, 12:54 PM

The ones in the truck of below the seat?

**MrChrysler** · 02-07-2016, 01:19 PM

Luggage compartment

**Mayorchuck** · 02-07-2016, 01:33 PM

Fuse 103 shows it's only used in diesel engines. If that's what you have, it shows it feeding the DDE relay, maybe even two depending on which set up you have.

K2003, X2085

rear RH side of engine compartment in electronics box

K2003	DDE relay
X2085	Component connector (9-pin, Black), DDE relay

**MrChrysler** · 02-07-2016, 01:52 PM

I dont have diesel... the title and then first post is saying that.

It's a picture from e39, but it's the same in my e38... On this picture is listed as F102 and it is wired in my car, showed on the picture.
I was counting the big one as well. So what is the 103.jpg

**Mayorchuck** · 02-07-2016, 02:03 PM

All I can find is going back to the '98 model and it's for the trailer module for RHD cars. It's used for the same thing on the '99 E39's. Could be the WDS is wrong. Wouldn't be the first time.

A6, X609

in RH side of luggage compartment

A6	Trailer module (AHM)
X609	Component connector (15-pin, Black), Trailer module (AHM)

**MrChrysler** · 02-07-2016, 02:36 PM

Any other ideas? So what is the fuse number that I have highlighted on the picture above... Is it 102 or 103?

**Mayorchuck** · 02-07-2016, 02:50 PM

The fuse you have the highlighted line going to is 103. All I found is in Post #15 above.

**Timm** · 02-07-2016, 03:42 PM

I think the counting of the fuses is extremely confusing - possibly the PO take a picture of his car! I think the fuse is 102 - which connects to a number of smaller fuses in the rear fuse box next to the battery. And of those, I reckon the one that connects to the alarm siren is the most likely - the fuses are:

Fuse 55 = General Module
Fuse 56 = Alarm Siren
Fuse 57 = Fuel Pump Relay
Fuse 58 = Rear lock, Tilt Sensor, Rear Mirror, Interior Protection Control
Fuse 59 = Rear Defogger Relay

Try measuring the current across those

**MrChrysler** · 02-07-2016, 04:10 PM

After removing them nothing happened, the current stays the same 0.33A.

When I disconnected the F103, F102... I dont know it's name... the car starts normal, and I could actually not find anything wrong with the car inside or outside... everything seems to be working fine.
Although I want to find the problem and fix it.

Timm... Could it be a fuse F103 not 102?

When I followed the cable from the fuse... it goes towards a rear seat, where it disappears from my vision.

**Timm** · 02-09-2016, 10:06 AM

Take a picture - it will life a lot easier!

**MrChrysler** · 02-09-2016, 06:19 PM

I need to take the front seat out. The cable from the fuse goes somewhere to the front of the car together with two very thick cables. They run next to the door but on the floor, underneath carpet.

**rudeboyE38** · 02-10-2016, 02:49 AM

Originally Posted by xlr8tin

This is a great question...Both 740's I've had did this. I learned that it was whenever I tried to lock it with the key fob. So I stopped using it and put the key in the door everytime. I haven't had the issue since. I think it has something to do with the EWS

I tried the same thing and it helped me out. What would be the problem?

**MrChrysler** · 11-08-2018, 03:32 PM

BTW... since noone knew what is the point of that cable, and because the cable disappears in the thick cable loom under the driver seat... I have simply removed the fuse. Everything works as usual. I still wonder what the cable is for.