Battery Drain, PLEASE HELP...
 

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

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.

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

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.

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?

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?

The battery is brand new, because of the drain. He checked the alternator and he said its fine. I am sure he looked at the starter, but i will ask him. He thinks it might be somewhere in the wiring, and that a mercedes dealer might have more of wiring diagrams.

I just dont trust going to dealers because they will charge you for everything they can possibly charge , and since we cant pinpoint the problem, i dont want the dealer to come back to me with an enormous bill telling me to change this and that , before diagnosing the exact problem.


I have my finger crossed, someone has gone through this, specially with a w140, and can help give me a good lead.

I apprecaite everyone's advice and help.

You didn't address what a couple of us have told you, that the mechanic can't do a "quick" resting current draw test, it takes awhile to do properly.
Also, since the battery was replaced, does the car still need to be jumpstarted? How long can you leave the car off and it will still start? Does it have to be shut off overnight, or just an hour, or how long??
Gilly

Gilly:


My mechanic waited for an hour or so, and he was still getting the drain.
Therefore, he unhooked the new battery after the test, so it wouldnt drain as well. So i cant answer the questions on how long was the car shut off, before needing another jump, etc....

Maybe the drain will not completely disable the starting power once the new battery is compeletly installed, and the car will function properly again. But that theory doesnt make sense to me.

I have an appointment with the MB dealer monday (Gilly that would be zimbrick, which i am sure your familiar with). I will post again what they find out.

I would remove the battery first,

then measure the resistance of the car circuits both ways from the main cables that go on the battery (with the batttery removed),

then remove one by one the fuses and sort out which circuit is draining.

May be you simply one light which is permanently on, and try to find it.

Be carefull, If you do not know how to do it don't do it.

good luck

Did you do a search? There are MANY threads on the subject of "Battery Drain".

Mike

Gilly, correct me if I'm wrong, but what I think you were saying is that you need to wait 1/2 hour with the battery connected to allow all systems to charge up their keep-alive memories and such. At that time, you need to test without interrupting power to said systems. Is that about right? If so, it's very much like we had to do at Cadillac back in the early 1990's. I've still got the multimeter test leads I jury-rigged that allow me to do that.

battery drain
 

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

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.

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