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  #1  
Old 05-20-2019, 10:39 PM
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Location: West Virginia
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Gretel is on a distinguished road
Elusive battery drain

Hello all,
This is my first post, but I am stumped after about 60 hours of diagnostic searching for a battery drain on my 2007 4.8i with most options. I was hoping I could list what I have found and someone might see a clue as to what it might be. So here goes:

No records of battery drain once everything goes to sleep (from Ista+ energy diagnosis)
Drain appears to be on terminal 30g (relay on rear power supply gets warm).

Things I have unplugged that did not stop the drain:
-not ignition key fob receptacle and start button
-not IHKR console
-not Nav DVD unit
-not CCC
-not CID
-not CA module in rear
-not trailer module
-not front hood switch
-not Rear HVAC control unit
-not Rear DVD display (FD)
-not Rear DVD unit
-not Stereo amp (rear/left cargo area)
-not driver door at all (unplugged entire door at jam)
-not other 3 door handles (unplugged CA plug)
-wire loom under passenger seat by sub woofer not pinched or compromised
-not TCU module
-not parking brake switch
-not any module in driver/rear cargo area - all unplugged
-not IBS
-not hazard button or central lock button
-not front center a/c vents
-not rear center a/c vents
-not FRM (although driver/rear hatch tail light corroded and not working)
-not RFK (rear facing camera)

Now, when I unplug fuse 39, the drain decreases. That is the only fuse that affects it. But that plug powers the CAS, which signals many other modules, so I found that inconclusive.

When I unplug the 41 pin connector on the CAS module, the drain decreases. (but the CAS controls so many other modules, I didn't think it was significant, or at least conclusive.

I checked continuity to ground of every wire coming off the 41 pin connector on the CAS to see if there was a power wire shorting. Here are my findings (by pin #)
1 - (signal-terminal 30g) - 42.4 ohms
2 - (brake light switch signal) - open circuit
3 - (driver's seat occupancy mat) - 15.6 M ohms
4 - (passenger's seat occupancy mat) - 5.1 M Ohms
5 - (crash safety module) - 75 k ohms
6 - not used
7 - (DME control terminal 15) - 91 ohms
8 - (Relay terminal 15) - 141 ohms
9 - not used
10 - (AUC sensor-terminal 15) - open circuit
11 - not used
12 - ground - .5 ohms
13 - not used
14 - (FRM - footwell module) - 166 M ohms
15 - (OBDII socket-terminal 15) - not used
16 - not used
17 - not used
18 - not used
19 - (terminal 15 wake-up signal) - .9 k ohms
20 - (DME control unit-vehicle immobilizer) - 10 k ohms
21 - (fuse 39) - open circuit
22 - (signal - starter-terminal 50) - 1.5 ohms
23 - n/a
24 - not used
25 - ground - .6 ohms
26 - (can-bus connector-low side) - Open circuit
27 - not used
28 - (DME control unit - signal engine start) - open circuit
29 - (hazard button/central locking button) - open circuit
30 - (PA bus connector) - open circuit
31 - (DSC - passenger/rear wheel speed) - open circuit
32 - (brake light switch signal) - 10 k ohms
33 - Aerial tuner with remote control receiver) - open loop (fault AO6C present)
34 - (fuse 10) - open circuit
35 - (CAN-bus connector-high line) - open circuit
36 - (DME control unit-terminal 15) - open circuit
37 - (TCU - on signal) - open circuit
38 - (bonnet contact) - open circuit
39 - not used
40 - not used
41 - (transmission control signal parked position) - 6 k ohms

Here what happens in terms of the time line:
system wakes up - 7.5 amp current drain
45 seconds after system wake up - 4.5 amp current drain
2 minutes after system wake up - .95 amps
3 minutes after system wake up - .666 amps

One last bit of info:
ISTA+ indicated 3 k-bus line non-communication fault codes:
RFK (rear facing camera)
FD (rear DVD display)
CID (Central Info Display)

Now, I checked the high and low bus line wires for voltage as well as continuity with ground (which they shouldn't have). The RFK, FD, and CID all function. Here are my results:

RFK (fuse 108)- high line - .5v (should be about 4.5v); .84 k ohms to ground
low line - .01v (should be about .5v); open circuit to ground

FD (fuse 107) - high line - 4.5v (within spec); open circuit to ground
low line - .49v (within spec); open circuit to ground

CID - high line - 4.47v (within spec); open circuit to ground
low line - .58v (within spec); 30 ohms to ground

Question: could the RFK be shorted enough to cause this large current drain?
The RFK bus line wires look shielded in the harness, so I am not sure
how.

I have reprogrammed the CAS with updated software ISTA-P 3.65.No change.

It looks like the dealer has done some rewiring from JBE to DME (wrapped with vinyl tape instead of cloth).

Anything that pops that I overlooked? I am about to give up.

I am very thankful for any expertise shared.
James
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  #2  
Old 06-01-2019, 11:31 AM
ard ard is offline
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Sorry I have nothing to add.

But what a fantastic first post!

Any suspicions about the IBS system?
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  #3  
Old 06-01-2019, 11:52 AM
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Join Date: Aug 2016
Location: Brooklyn, NYC, NY
Posts: 336
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Don't know about the 4.8 but the 35d does have a big drain for a few minutes when you open the doors because the e70 was programmed by a moron to run things that aren't needed without key in.
This was observed on a friend's e70 35d too. It's only for a few minutes like you have observed.
Friend's e60 doesn't drain this much and doesn't complain so much despite being barely driven..

My battery drain turned out to not be the drain but the ibs being OCD about voltage on my normal flooded battery. If you look up the ista diagnosis for battery charge level histogram, you will see that this is what it's complaining about, not an actual drain. The stupid thing is that I too was chasing a drain which ista showed didn't exist, but in fact was complaining about voltage/charge level. Flooded batteries have a lower resting voltage level than agm.

It was happening for me even with a brand new flooded battery that tested well. It was less often but it still happened. Crazy...

I think they never programmed the proper expected voltages for flooded batteries even when it was coded as such. So if you are not running an agm, this could be your issue. I replaced with an agm battery, coded to agm 90ah and haven't had messages since.
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  #4  
Old 06-01-2019, 09:00 PM
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Join Date: Jun 2016
Location: West Virginia
Posts: 2
Gretel is on a distinguished road
Solved.
Ard, I unplugged the IBS and noted no change.
Thanks Robnitro for the helpful info. Knowing that it should be drawing that much current for the first few minutes after waking up is helpful. So I began to look for a smaller drain while it slept, even though ISTA energy diagnosis showed no occurances of it. So, with all doors closed, and the rear hatch latch latched two clicks (so it thinks it is closed and goes to sleep), I put my known good battery from my e53 in the e70 and did some more testing. Watching battery voltage, I removed fuses, looking for increased voltage drop. I unplugged the CA go module, and the battery voltage stopped falling.
With CA go module plugged in, I removed all four door handles again, and voltage continued to drop. I unplugged the CA go module again, and voltage stopped dropping. I left the CA module unplugged overnight, and battery stayed charged. I plugged it in, and the battery went flat. So there it is. The CA go module is shorting out and draining the battery. It is too slight to register in the ISTA energy diagnosis, but enough to kill a battery. I missed this the first time because I was looking for a reduction of current the first 3 minutes of wake up. Ideally, I should have measured voltage drop across each fuse (with the fuses in place) while vehicle was sleeping and then using a voltage drop to current chart, determined the parasitic draw. The thing that threw off all my diagnosis was the 7amp initial draw. I thought it was too much, but apparently it is correct. I will be getting an AGM battery. I believe you are correct, robnitro, about these electrical systems being too much for a lead-acid battery. I hope the figures in my first post will be helpful to someone in the future who wants to compare their numbers to those of another car. I do still want to ferret out the 3 broken/grounded k-bus wires, but that is for another day.
Sincere thanks,
James
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  #5  
Old 06-02-2019, 10:46 AM
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I don't get why ibs doesn't see a drain overnight through CA. It's designed to see loads of 70ma (iitc) and report that to the dde when you start up (after battery shutdown reset) .
Again these cars are done badly because a load that brings the battery to danger zone overnight would be way more than 70ma or whatever ibs reports as maximum safe drain!

You got it reported as a drain, but really it was just looking at voltage and tripped on that, despite it having the ability to read tiny currents and tell you. It's programmed badly and the e60, etc don't have this issue.
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