Hey all, I'm new to posting on MB world, but am a frequent reader recently due to a current draw issue.

In short:
- 3A current draw when the ignition is off
- Have done current draw test by removing fuses one by one, and no noticable current drop
- AVR shows that battery, starter and alternator are working properly
- Have done AC voltage test on alternator
- Have unplugged seat modules and draw is still there

Details below:

My problems started 3 weeks again when my car wouldn't start and I needed a boost, I thought maybe it was just a really hot day. The problem persisted the next day. In checking out my battery, it was the old stock battery from 2003 so I figured it was time to replace it.

After I replaced the battery, it drove fine for 2 days, and it wouldn't turn over. So got a boost and started to investigate what was wrong.

The following day, I got an AVR test that showed everything (alternative, starter & battery) was in working order, but as expected they said that the battery was low and just needed charging.

In reading all the posts, I noticed that the 2 biggest culprits for current draws were the seat modules and interior lights. One night after knowing that I had decent charge in the battery (because I drove alot that day), I double checked all my interior lights and unplugged the seat modules. The next day, same current drain.

So I decided to do a current draw test on the car, as per suggested in several posts. I connected a multimeter in series with the battery, and noticed a current draw of 3A, which from what I've read is really high. So I started pulling fuses from the 3 fuse panels around the car (under the hood, side of teh door and in the trunk). removing them one by one while montioring the current draw. There was minimal change (by 10-20 milli-amps change only) occuring when fuses were removed one by one.

I then double check all the interior and exterior lights again and noticed that the glove box wasn't able to close all the way, leaving the glove box light on (I can see from the cracks). So I removed the bulb thinking that was the problem.

The next morning, the battery was dead again.

I then read that another culprit was the leaky or faulty diode in an alternator. So I did the test for AC voltage across the battery when the car was running and when it was off. I didn't show any AC voltage in either scenerios.

I'm in a bit of a loss right now. Not sure what is going on.

- Could my current draw test conditions been non-ideal? I've done it twice, with the battery almost dead, and with the battery about 50% charged, and no noticable current drop (from 3A)
- Is there anything else connected to the glovebox that would stay on if the door wasn't closed all the way. I just thought of this, and will monitor current draw when physically pushing the button that gets pushed when the door is fully closed.

Any other thoughts?? I'm trying to avoid taking it to the shop until I can isolate the issue. I've read the horror stories of mechanics that just replace stuff with a trial and error mindset without true diagnosis.

JesterBoy (bummed out and frustrated)

 

FYI, the car is completely stock. I'm the second owner of this car, and am not aware of any after market additions to this car.

 

If you could buy, beg or borrow a clamp-on DC (Hall effect) current meter, then you might be able to chase the 3A current through the harness without having to disassemble everything.

The meter would have to be one with enough sensitivity to provide a usable scale (e.g. 10 or 20A full scale, not 1000A). Absolute accuracy wouldn't much matter so long as you can distinguish the amps and where they're going.

if not that approach, then you'd have to start opening up circuits by disassembling the connection points. Use a binary search pattern to hone in on the leak. You'd have to be very careful to avoid disastrous shorts with all the loose cables.

 

Jeffy,

I'll look into obtaining a clamp on DC (Hall effect) current meter, any idea how expensive they are?

Once I get one, where should I start??

From your experience, any idea where the 3A can come from?? That's a pretty big draw. Another thing that I'm also contemplating is what kind of condition the charge should be on the battery. I've done the currrent draw test twice, and both times, it was with the battery at a very minimal charge. Should I do being the test with at least 50% charge?

 

If you have 3A current even with a minimal charge on the battery (how many volts?), then the current will almost certainly increase in proportion to the voltage. Let's say, for example, it's about 5A leakage current with the battery at full voltage (about 12 to 13 volts). That's about 60 watts going up as heat somewhere. Geesh, can you borrow an infrared thermal imaging camera? If the car was cool, then a 60 watt hot spot should show up easily. Or just follow the smoke. :-(

I can't recommend a particular clamp meter. Good ones are probably too expensive and cheap ones are unknowns. Cheap and good ones might take many weeks to arrive.

If it was me, I'd be reading magazines in the dealer's waiting area while they sorted it out. I assume a good pro (with the right gear and documentation) would only need a few hours labour to find the problem.

But standby in case others have better advice.

 

Jeffy, are you suggesting that perhaps my battery is losing charge or not being able to hold charge?

I've currently got my battery out of circuit right now and is trickle charging. From my experience a week ago, I had charged the battery for about 14 hours at 2A charge rate. And from the digital display it said 62% at 12.7V. This seemed rather low given the time of charge, as I've read that typically you can charge a battery to 100% or close to it over night.

I had considered the fact that it might not have been a system current charge at all, but rather the inability for the battery to hold a charge. However, the battery is practically brand new (2 weeks) but I know that between now and when I bought it I had drained it a handful of times before I found that teh glove box light was on. But at 3A, you're right, there would be smoke across a 12V battery.

Something else that I've noticed on the charge cycle is that my charger will tell me a particular status of the battery, but once I pull the plug, and replug it in, the status is a number that is lower than when it was charging. Can I attest this to it getting to steady state? Another thing is that while monitoring the battery (not charging), it seems to be counting down a little bit in % charged (I noticed from 42 to 25%), that's almost showing me that the battery isn't holding it's charge? Or again, is this a steady state issue?

Thoughts?

 

Your car shouldn't be drawing 3+A current once it's totally shut down. If that measurement is true, then your battery hasn't got a chance - it would be pretty much flat each morning.

 

3A draw is definitely happening, as I've done a current draw test. I'm just not too sure what could cause such a draw. As I mentioned before, I've done the current draw test by setting up a multi-meter in series with the battery, while monitoring the current. One by one, I've removed each and every fuse and relay that's visible in the 3 fuse panels, and nothing reduced the current more than a 10-20 milli-Amps.

 

Go ahead and get that battery charged to 100% before testing. If still hooked to the vehicle charge at 10 amps. Your 3 amp draw is taking it out faster than your 2 amp charger will supply. If you think about it your alternator is charging your system at a lot faster rate than this (60 amp+).
You say you have pulled the fuses 1 at a time, do you have more than 1 fuse box? I know mine does.
This is why it gets expensive to have a mechanic do this, It takes alot of chasing to locate the issue some times.
You can't take anything for granted, and some systems like the one going to your starter are not fused!
Good luck!!!

 

Quick update. I got my battery checked out (bought 3 weeks ago), and it apparently had a bad cell in it. So I got it replaced. Ater installing it, the current draw was still there at 3.4A.

I did the current draw test again, now with a fully charged battery and removed every fuse one by one in all 3 fuses boxes (engine compartment, cabin and trunk) and nothing reduced the current draw beyond a 10-20mA. So the draw (3.4A) is still there.

Any other thoughts?

 

When a multicell battery (like a 6-cell car battery) is discharged way-too-far, if one cell has slightly less A-hr capacity than the others, then the others will continue to drive current through the circuit even after the weakest cell has already reached zero. So the weakest cell can be driven past zero into polarity reversal. That's not good for it.

Given your 3.4A leak, left draining overnight, it's very likely that this problem killed the cell.

Perhaps you should get one of those quick disconnects for the car battery + terminal so that you can disconnect your battery when you're parked.

The battery dealer is going to be very suspicious if you show up a second time. As is likely to happen unless you take steps to avoid it.

 

Have you checked your car's alternator? The reason I ask is that there's no fuse between the alternator and the battery. Maybe a bad (leaking) diode.

 

I've checked that with a mulitmeter. I've checked that it's charging properly (over 14V) and I've checked for AC voltage (what a diode leak would look like).

 

It is built in the Alternator and you would not spot it doing a voltage check most likely. When you disconect the heavy gage wire on the alternator, check for a draw between that terminal and the heavy gage wire. This is what feeds power back to your battery normally. Good chance this is your draw.

 

Dan explained it. You wouldn't see a 3.4A leaky diode except as he described.

If the alternator is bad, then find a good local alternatir rebuilding shop. I've had them fixed (rebuilt) for well under $100 and less than an hour, keeping the same unit.

Good luck.

 

I read somewhere that you can detect a leaky diode or faulty diode in an alternator by checking the AC voltage across the battery terminal, as the leak would be in the form of AC voltage. I did that an did not detect any AC voltage at all.

So you are suggesting that I check for current from the heavy gauge wire on the alternator to the negative battery terminal?? If not, what terminal are you referring to?? Sorry for the ignorant question. I'm not very knowledgable on cars. Would a simpler test be to disconnect the alternator circuit and do a typical current draw test on the battery?

 

Yes.

Disconnect the battery first.

Then disconnect the alternator and make sure the cable is protected from shorting to ground.

Then re-run your same old battery leakage test to see if it's still there or not.

This is like 'pulling' the alternator - same as pulling all those fuses.

 

I think this test is out of my abilities. I'll take it to the shop to get this done.

Jeff, from what I've posted thus far, is it safe for me to assume that it's not an electrical subsystem (seat module, fans, computer, etc) that's causing the problem because I've essentially eliminated that from the fuse currrent draw test.

Which leaves either some bad wiring, alternator or starter?

Wyler

 

It's safe to rule-out any circuit where you pulled the fuse. You probably got all the fuses, but we can't be certain.

Keep in mind - if the alternator is the cause, rebuilding might be very cheap (depending on your local alternator shop).

Good luck - hopefully it won't cost too much to fix.

 

The best way to go about tracking down your draw would be to use an amp clamp as described above (ex: Snap-on EETA308A or equivelent). Also as stated verify it is a low amp probe. You can then place this probe on each terminal of the front backup fuse box (F32) and the cable going to the starter/alternator.

A few notes regarding quiescent current draw:
-An acceptable current draw for a 203 chassis is 50-60mA(or lower)
-Before testing be sure all door pin switches are closed
-Be sure that the CAN is asleep, or that it is going to sleep(this could be the issue if it does not sleep)
-Anytime you unplug a fuse or component the CAN wakes up
-A 203 chassis can take 15-45min to sleep, which means you can not draw test until after that time
-When performing quiescent current draw testing you want to be as least invasive as possible, hence the amp clamp
-For testing draw of individual circuits, rather than unplugging fuses(very invasive) measure voltage drop across the fuse, and then use ohms law to compute the actual current flowing through that circuit. (to do this procedure you will need a DVOM that measures µV, micro volts, ex: Fluke 189) you will also need to know the nominal resistance of the fuses available from StarTek info

F32 distributes battery voltage to interior fuse box (F34), Front SAM (N10/1), Rear SAM N10/2, and engine fan M4/7. When you have found the cable causing your draw, you know you can now focus on that area. You can now use the procedure mentioned above. if none of the fuses show a draw, it could be the alternator, or internal draw from one of the SAM's.

If you can understand this procedure and have the tools to do it, this is by far the quickest way to track down a quiescent current draw. There are further ways to test draw utilizing CAN testers, but as you can imagine these tools are not readily available and are not cheap. (CAN testers are integrated in to the Star Diagnosis Compact 4 with SDconnect multiplexers)

 

I have a 2002 Mercedes C320. My battery is dead after seating overnight. Took the car to the Austin MB dealership to diagnose the problem. I was told that the power seat motor is draining my battery. Both seats. Come to find out that many other people have experienced the same problem.

I called Mercedes USA and they said that since the car is out of warranty, there is not much they can do. That is bull!! Obviously since so many people with this car model have the same problem, it has to be a manufacturer fault.

I was wondering how many people need to experience this problem before Mercedes will admit that they have a bad component on this model.

I figured,if enough people call and tell MB that they have this same problem, they will realize that this is a defective part and they will issue a recall and pay for necessary repairs.

Please call Mercedes USA and report this problem. 1-800-FOR-MERCEDES (1-800-367-6372) or 201-476-6200

 

As soon as I got home from buying a used 2003 C320 3.2 L V6 EFI Sport Sedan 4D yesterday, I looked up forums such as this, as the battery was dead even before I drove it off the lot ! I was scared to see that MANY people have this problem, draining power from the seats - or who knows where. It was also dead this morning when I went to drive to work and had to call AAA. They re-charged the battery so I was OK, but for it to be drained two days in a row is more than worrisome!!!
Is there a class action suit that could be organized from here on this model, or should I just return it to the dealership since this problem has occured twice within 48 hours and be protectedby the "Lemon" clause? PLEASE ADVISE! Thanks a million!

 

Same thing happened to me I have 2001 MB C320. I changed the battery and the brand new MB battery got empty in 3 days. After jump-starting the car driver seat stopped moving. I unplugged the wires under the seat and after I reconnected them, the seat moves again.

More than one person said that I should rebuild the car alternator.

 

The C320 has a problem with faulty design on the seat controller modul , hope enough people will call 1-800-FOR-MERCEDES (1-800-367-6372) or 201-476-6200 , To ask for a recall to correct the problem in almost every car including mine .