Battery Drain, PLEASE HELP... - PeachParts Mercedes-Benz Forum

chytaan · #1 10-28-2006, 12:11 AM

Hello:

I own a 1997 Mercedes S600. The last few weeks, my battery would need to be jumped everytime, i need to start the car. Then when i turned ignition off, i couldnt start the car again, unless i jumped my car.

I took my car to my mechanic, he said that my battery was completely gone. I purchased a new battery, but before my mechanic could install it, he checked for a drain and found one.

He put the ammeter to the negative wire, to see if there is a drain, before installing the new battery, and there was a reading of 0.1 or something to that affect. He told me that it should be around 0.01, but not that big of a draw like i am getting.

Then he did the usual, pulled out each fuse, to see what is causing it, but nothing came out definitely. He even tested the aftermarket stereo, but it was only getting out around 0.02 . There is something that is drawing around 0.1, and its not the fuse according to him, and that a lightbulb should not draw that much.

Can someone suggest what might cause this?

I did some search, and read that something in the alternator components might be the cause, other suggested a corrupt positive terminal wire, some suggest alarm system or climate control..

Any other suggestion on what would be causing such a large drain????

ANY suggestion appreciated.

Thanks in advance

wbain5280 · #2 10-28-2006, 12:22 AM

Remove each fuse one by one, put your amp meter, actually a digital voltmeter or an analog one for that matter, and put the probes across the contacts. Measure the amperage and write it down. Look at the resulting table and see which one has the most current. See what systems are on the circuit in question. You can post the results if necessary so we can help you. Modern cars use lots of electricity for things like engine computers, climate control computers, transmission computers, instrument computers, body computers, stereo systems, which are little computers... You get the idea.

Gilly · #3 10-28-2006, 06:40 AM

He has to wait on a 140 car about 1/2 hour or more to wait for all the consumers to go into an idle mode. This is tough to do properly on a 140. If you are OK with it, I'd take the car and see how it does in "the real world". I assume he's saying .1 amp resting current draw, which (other can check me here) is 100ma (milliamps)? 1000ma = 1 amp right? On a 140 it's not uncommon to be as high as 30-40ma, but on most other cars it's maybe 10-20ma, 140's have alot of computers.
If your mechanic needs a few details on doing that test let me know. Or is he an MB guy and should know? Also, if he's doing the test right, have him make sure all the various interior lights are off, although 100ma seems low to be a bulb.
Gilly

wbain5280 · #4 10-28-2006, 06:46 AM

Agreed. He should measure the current right after he turns the car off and then wait another hour or hour and a half before measuring again. COmpare figures.

he could have a weak alternator, needs a regulator, or a broken wire in the field wire or a fusable link somewhere.

chytaan · #5 11-10-2006, 01:17 PM

We still cant figure it out.

My mechanic checked all the fuses, the alternator, and waited over an hour when measuring the current draw, and is still getting 0.1.

Any more ideas, before i give up and take it to the dealer?

Two560Two · #6 11-10-2006, 04:47 PM

my friend had the same issue with his 560sel. Everything checked out ok, except mech found the starter to be grounded and alternator too old. changed both of those and the car runs fine. See if you have a ground anywhere, or maybe your battery just need replacing?

5cylnoplugs · #7 11-13-2006, 01:23 PM

I had a 300d with a battery drain. I unplugged the power antenna and fixed it. You might give it a try

chytaan · #8 11-13-2006, 02:39 PM

I did the search on battery drain. I actually showed my mechanic this thread at his shop. He is generally very good and technical, and usually can fix any problem with my cars with no issues, but this one he couldnt get to the root of it.

I am thinking it has to be something simple that was overlooked, whether it has to do with the actual procedure of the test or an item not tested properly.

Anyhow, the car is at the mercedes dealer right now. They are supposed to get back to me this afternoon on what they find. Hopefully, they can diagnose exactly whats wrong. Once i find out, i will report back here on the results.

Thanks for everyone's help and advice. Its truely appreciated.

Gilly · #9 11-13-2006, 11:10 PM

MoneyPit: You connect an ammeter between the neg post of the battery and the neg cable and watch the current draw. Accomplishes the same thing as leaving the battery connected, doesn't require and special wire-rigging. If you have a multiple scale ammeter you are accomplishing the same thing. The components should function just fine through the ammeter, up to a few amps.
Gilly

chytaan · #10 11-14-2006, 10:02 AM

Well, i picked up my car from the mercedes dealer and he basically said the same thing as my mechanic. He said he got about .1 draw, but he couldnt find a specific drain. He also added that its normal for some w140 to do this. (which i doubt, since i have owned several 140's and this is a first).

The advisor also added, that the battery will go to a low level if the vehicle is not started within a week. So he recommended regular start up.

Not the answer i was looking for, as my mechanic and I did the same test, and was hoping the dealer would find something we overlooked.

My mechanic suggested, that i leave my car for a day not started, and then try to start it, then for couple more days not started and start it again, just to see how long before we have difficulty starting it again.

Anyhow, thanks for everyone's help, much appreciated.

gmercoleza · #11 11-14-2006, 11:03 AM

Just as a suggestion, you might try installing a battery tender in the meantime, to avoid needing a jump every time this happens.

sixto · #12 11-24-2006, 02:54 AM

chytaan, if your S600 is anything like my 300SD, ahead of and above the battery is a distribution center. The positive cable splits into a couple of small cables and a big cable. One small cable goes to the fuse box above the battery. The other small cable and the big cable go the passenger footwell where there is another distribution center. From the front distribution center a small cable goes to the alternator, another to the starter, then there's a series of smaller wires I haven't investigated. I assume something goes to the ECU cluster and the front fuse box.

What's the point of this? Pulling fuses in a W140 might not localize a ground fault because the systems are interconnected. How the fuses even function as fuses is a mystery to me. Maybe your mechanic can isolate the circuit by disconnecting cables at these distribution centers.

In my case I'm chasing a draw that discharges my battery overnight. I localized it to the small cable that goes to the rear fusebox. I get the draw if any of a particular set of 5 or 6 fuses is in place. I haven't figured out what that set of fuses have in common (stereo, convenience module, and something else).

Sixto
93 300SD

Moneypit SEL · #13 11-14-2006, 11:21 PM

Quote:

Originally Posted by Gilly

MoneyPit: You connect an ammeter between the neg post of the battery and the neg cable and watch the current draw. Accomplishes the same thing as leaving the battery connected, doesn't require and special wire-rigging. If you have a multiple scale ammeter you are accomplishing the same thing. The components should function just fine through the ammeter, up to a few amps.
Gilly

Ahhh. I recalled a detail after I posted that. Caddys had an issue where excessive current draw would not occur until after the components were powered up. Disconnecting the battery reset everything and hid the problem. The jury-rigged test leads were to permit cycling the ignition key to power up everything without blowing the fuses in the multimeter.