[W126 Coupe] Update on Battery Drain
Gregory Tchilinguirian
GT320i at aol.com
Tue Feb 21 00:40:18 EST 2006
Hi Vance,
First I would check out the starter and solenoid. Next I would check out
the fuse box again with a slightly different strategy; I would remove all of
the fuses and check the condition of the battery with a volt meter. I would
do this both when you remove them (which should occur when you normally park
your car for the night), and once again in the morning (before you normally
leave). After you have your readings then replace the fuses and go to work
(or jump-start the car and skip ahead a paragraph).
If the battery hasn't lost its charge by the next morning with all of the
fuses removed, then each night you can add fuses bank by bank until the
battery experiences a sudden drain. You can then narrow it down by adding a
fuse each night until you find the suspect(s). The answer should be in the
numbers. It is entirely possible that it could be a number of circuits
contributing to the large intermittent drain.
I would also do this with the battery completely disconnected. Assuming
that temperatures are within the same range both nights (or better yet, park
it in a garage), you should be able to verify a number of things about its
condition; like an intermittent internal short for example.
If all of the above efforts fail, you can assume that the drain is a device
that connects directly to the battery. I have no idea how many of these
exist or were added to your particular car, but you should be able to spot
any aftermarket stuff and disconnect it pretty easily. Be through. Once, I
found an Audiovox CB radio that must have had some kind of remote control or
another component (which was nowhere to be found) under the dash of one of
my cars. It was a plain looking black box which blended in pretty well.
Its removal was warranted due to the fact that it was still plugged in and
totally useless and could potentially cause problems. So check everywhere
and make sure you get all of those types of items disconnected. The factory
installed unfused battery connections can be discovered through a review of
the ETM, schematics or something else along those lines.
Greg Tchilinguirian
83 380 sec
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From: "Vance Rowley" <vance.rowley at tiscali.co.uk>
To: <mbcoupes at mbcoupes.com>
Sent: Monday, February 20, 2006 8:17 PM
Subject: [W126 Coupe] Update on Battery Drain
> Hi Guys,
>
>
> I am almost at a loss on this one. I contacted my local Meta dealer and
> spoke at length with him regarding the possibility of my alarm/immobilizer
> being the problem. Basically the answer is 99.9% chance it isn't. I also
> looked on some forums and found the backup battery is built into the alarm
> sounding unit. I have already run a test with this disconnected, but this
> intermittent current draw was still there, so there goes the theory of the
> backup battery taking the current.
>
> I have tried replacing all the fuses that are "hot at all times" with 1amp
> fuses. Left them in overnight, but all were still OK next day, but the
> current draw had obviously happened overnight as the engine only just
> turned over. I even went to my local car accessory place and did another
> drop test on the battery, hoping that although my last tests showed the
> battery was OK, that maybe I was mistaken somehow. It tested perfectly and
> yes it's charging perfectly too.
>
> It looks like something that must be connected on "the other side of the
> fuses" that must be taking this intermittent current draw, comming
> directly from the battery. The factory alarm is disconnected completely.
> This was done when the Meta system was fitted and this problem, although
> has being going on for years, it hasn't always been there. I have had the
> car parked up (shortly after I bought it) for two weeks with the alarm
> armed and when I returned and started it, it was as if it started on a
> brand new battery.
>
> I have even completely had the after market stereo system disconnected in
> case for some reason this might take an intermittent current draw. No luck
> there either. The normal current draw at the battery terminal is at
> between 85ma and 90ma with the alarm / immobilizer armed and everything
> connected. But something is taking this intermittent 6amps or so now and
> then. I even stood watching the meter (connected between the battery and
> terminal) for nearly an hour today, but didn't even see this once within
> this time period. In the past I have seen it, but it's so intermittent,
> you have got to be very lucky to be in the position to measure and see it.
> Even then, because it's not there all the time, what chance is there of
> finding out what it is?
>
> As you know from previous posts, I have ruled out the vacuum pump that
> feeds the central locking system and all of the normal checks have been
> made, but there is nothing in the archives (at least not until now) on an
> intermittent problem like this one. I am basically out of ideas. Am I the
> only one with a 560SEC that this has happened to? I welcome any ideas and
> I am at a stage where I would not consider any idea a stupid one. The only
> idea I have myself is to just drive it every day, which is what I used to
> do, so that idea is ruled out at the moment. And yes, the other idea is to
> disconnect the battery when not in use. This I was doing, but by ideas and
> suggestions, I mean to find the problem, not just cure the symptoms.
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