2005 E320 CDI battery drain

[mb_e320]

I have had a problem with my battery draining twice. The first time the car was towed to one dealership and they replaced the battery. It just happened again a couple months later and I took it to my dealership. They said they measured a drain one day, but the drain stopped & they could not find the source. The battery was replaced again & vehicle was returned.
I am worried this will happen again as the source of the problem was not found.
Has anyone experienced this & what was done to fix it?
Thanks for the help.

 

[124coupe]

Eliminate after-market stuff first (e.g. do you have a 3rd party car phone kit as these are sometimes wrongly powered?).

 

[television]

95 % of battery faults are within the battery itself. In order to find a drain it is important that the circuit is not broken when inserting the ammeter, by using a meter with a double lead, a probe and a clamp, slacken the bolt on the clamp on the battery. Hold the probe onto the center pole on the battery,slide the clamp up,take the second lead with the clamp and fix to battery pole terminal, result,circuit not broken.
A fault in the networking Command is becoming common when the is a fault in the MOST bus that wakes it all up,and puts it to sleep.

Malcolm

 

[mb_e320]

Steve: There is no after market items on the car, and the cell phone only gets charged and plugged in when the car is running. (the cell phone also is not connected to the vehicle phone system.)

Malcolm: I am guessing that the problem is not with the battery as the battery has been replaced now for the second time.
I don't quite understand what you mean by "A fault in the networking Command is becoming common when the is a fault in the MOST bus that wakes it all up,and puts it to sleep." Are you suggesting that it could be an issue with one of the computers & not shutting down power to something?

Thanks for your input on this guys - I will check back in later to see if there is more input.
Matt

 

[mioba]

had a similar problem with my w220 soon after i got it, as soon as i got in all the aux electricals would turn off to save battery.

happened a few times so i went to the dealers,

they flashed some software and its been ok eversince.

 

[Captain Flack]

My C270CDI's flat battery was down to a faulty module under the drivers seat(controls seat/mirror adjustment). I don't know how the dealer discovered it but while we were waiting for the replacement part they just left it unplugged and it solved the problem. It won't do any harm to unplug it and see if it works.

 

[television]

Steve: There is no after market items on the car, and the cell phone only gets charged and plugged in when the car is running. (the cell phone also is not connected to the vehicle phone system.)

Malcolm: I am guessing that the problem is not with the battery as the battery has been replaced now for the second time.
I don't quite understand what you mean by "A fault in the networking Command is becoming common when the is a fault in the MOST bus that wakes it all up,and puts it to sleep." Are you suggesting that it could be an issue with one of the computers & not shutting down power to something?

Thanks for your input on this guys - I will check back in later to see if there is more input.
Matt

The Command and all of the bits and pieces around like the CD changer shut down 10mins roughly after the car is stopped and locked, these consumer bits have the" MOST BUS" This is another system like the CAN BUS, a built in self check sometimes it does not go to sleep and runs until the consumer battery where there are two, drops to 11 .5 volt and then the system turns off. You could sit in the car for 10 mins and listen for any clicks or fans starting, its a long shot and there is more things, but you have to start somewhere.
I would have checked with an ammeter, that tells all, then just take each fuse out one by one, and you come to it.

Malcolm

 

[mb_e320]

I will try those ideas this weekend - I will first see if the new battery has a drain, and then start with disconnecting the seat module first which should be the easiest item to start with.
Thanks for your input everyone,
Matt

 

[eric242340]

This is a common problem, try the telephone interface under the right rear seat. disconnect it and check for battery drain.