[aorrdalca]

I have an otherwise perfect 2004 E320 wagon. A few months ago I left the key in the ignition, came out to find the car dead, boosted it, no sweat ... since then, however, big problems. The battery slowly drains over 24 - 36 hours, and the car then won't start. It is not the alternator. It is not the battery. When the current is measured out of the battery, it has a minimal draw. It's as if some computer wakes up in the middle of the night, draws a lot of power, and sucks the battery dry. One wonders whether the initial event, where the battery was drained by the key in the ignition, caused some software problem that has produced my current woes. I have a very good, experienced mechanic who is also stumped.

I've read of other people posting similar problems, but little in the way of answers ... anyone have any suggestions?

 

[Twobig]

Sound like a short ciruit causing a continuous drain on the battery, check for loose, broken or faulty wires in the charging circuit. I know you checked the cables. How old is this battery and did you check the electrolyte in the battery?

 

[baddsm]

pull a bunch of fuses like radio fuses and other items like interior light fuses, etc. Let car sit and see if problem reoccurs. If it doesnt add one fuse back at a time each night until the battery goes dead. Ding!

 

[keyhole]

If it's the original factory-fitted battery, it will be 6 years old now and coming to the end of it's useful life.

I have found car battery behaviour can be deceptive... you think that you have charged it, but it does not hold the charge. Typical sign of a battery that is dying.

Don't waste any more time on it. Buy another.

 

[Twobig]

If it's the original factory-fitted battery, it will be 6 years old now and coming to the end of it's useful life.

I have found car battery behaviour can be deceptive... you think that you have charged it, but it does not hold the charge. Typical sign of a battery that is dying.

Don't waste any more time on it. Buy another.

I agree with Keyhole on this, get a new one and go from their.

 

[aorrdalca]

It's not the battery ...

The battery was replaced with a brand new one; the problem did not go away. With respect to the suggestion that there's a short circuit, as I said, the current draw on the battery when the car is off is very low - milliamps. Something seems to happen in the night with systems turning themselves on. It would be nice to have a device that could monitor power useage over a period of time but I don't know if this exists or not.

 

[Diesel Benz]

The battery was replaced with a brand new one; the problem did not go away. With respect to the suggestion that there's a short circuit, as I said, the current draw on the battery when the car is off is very low - milliamps. Something seems to happen in the night with systems turning themselves on. It would be nice to have a device that could monitor power useage over a period of time but I don't know if this exists or not.

It should be extremely unlikely that the current drain increases suddenly at night but there are several issues that more or less randomly cause additional current drain. You might follow the "plug off fuses" approach or since you can measure the quiescent current, you might do that (without interrupting power towards the car) a few times and you might find once the current is too high. Then you could again pull out fuses to figure out when the current drain stops.

If you have power seats, you could plug off the control units, these are a common source for the power drain.

 

[Streetglower]

dealing with some draws on these cars can be hard. at the dealer we now have the SD scan which hooks into the can network and monitors a list of the control units in the car and the machine is left hooked to the car overnight and if one unit wakes up the tool catches it and records it.

but when your mechanic checks the car what is the reading when the car has gone to sleep????

 

[aorrdalca]

Sleeping battery draw

When the car sleeps, the draw is ~ 20-30 mA. I'm not sure whether my mechanic, who is very good and has lots of experience with MB, has an SD scan, but is this something that can be done in '04 models? I seem to remember that MB recently beefed up the on-board power diagnostics, probably in response to complaints like this.

I have seen a number of other posts like mine, and many seem to have as a precipitating event the inadvertent flattening of the battery.

dealing with some draws on these cars can be hard. at the dealer we now have the SD scan which hooks into the can network and monitors a list of the control units in the car and the machine is left hooked to the car overnight and if one unit wakes up the tool catches it and records it.

but when your mechanic checks the car what is the reading when the car has gone to sleep????

 

[keyhole]

OK - we belatedly learnt that you have a brand-new battery.....

Let's ask another question. Do you have COMAND with Nav?

 

[aorrdalca]

Not the battery, no COMAND

The initial post did say that it wasn't the battery, but I should have stated explicitly that I'd replaced it.

I do not have COMAND with Nav.

My mechanic says that some of the circuitry in the car (mainly computers, I gather) is unfused and capable of draining the battery overnight.

OK - we belatedly learnt that you have a brand-new battery.....

Let's ask another question. Do you have COMAND with Nav?

 

[Streetglower]

When the car sleeps, the draw is ~ 20-30 mA. I'm not sure whether my mechanic, who is very good and has lots of experience with MB, has an SD scan, but is this something that can be done in '04 models? I seem to remember that MB recently beefed up the on-board power diagnostics, probably in response to complaints like this.

I have seen a number of other posts like mine, and many seem to have as a precipitating event the inadvertent flattening of the battery.

20-30ma is well within spec. on your car when everything is asleep you should see between 10-80ma, if you see over 100ma then something small is staying on. usually main computers that arent going to sleep draw over 500ma to several amps. now everything in the car is fused. there are no control units that arent fused. all units have a power supply and that power supply is fused which comes from a main fuse box. now if the car dies after a day or so with a new battery then the draw shouldnt be hard to catch. sometimes you have to keep watching the meter as the readings will jump. this is where the sd scan comes in it does the monitoring for you so you can do other things. more then likely an indy mechanic wont have the software, in that case he will need to watch the meter for a jump in the readings. but again 20-30 ma is a good reading.