C-class battery drain
 

I'm a new owner of a 2002 C-320. The battery has been drained down twice. Battery and charging are super fine. Should the current go to zero after some wait on these cars???

Found some wierd stuff going on with key out, doors closed, display off:

Have a 1.2 Amp discharge and soft buzzing from overhead consol
Thought maybe the tempsensing pump running, but sound stops with sunroof, domelight fuse #9 pulled. Current drops maybe 0.1.

pulling the fuses helped by .1 or .2 per fuse for 5 or 6 fuses near the steering wheel, but can't eliminate the last .03 or so. These fuses go to the central locking system.

Need help, what am I missing!

Five or six fuses......
 

each drawing 200 ma or so would do it. Does that car use electrical power or vacuum for locking/unlocking? If electrical, sounds like the controller for the system might be at fault assuming that the fuses belong to that system.

That car has an interior network of computers.
Most likely 1 or 2 of them aren't going into the "sleep" mode.

Most common culprits are the seat modules & rear SAM (signal activation module)
Give at least 5 minutes after disconnecting to see if the rest of the network will go to sleep.

seat module is well known red flag for your model/year(s). have it checked...

http://www.mbworld.org/forums/showthread.php?referrerid=29694&t=91258

Sounds right. Can someone recommend a CD manual so I can find the modules?

Its a little tricky to trouble shoot. I had to block the drive door switch to get the car to go to sleep. Should it only take 5 minutes? I came out yesterday after about an hour and total current dropped to .1A

What should the sleeping current be?

Is it then good trouble shooting to pull fuses to see which one is still drawing current??

I'd be afraid to leave this parked for a week with .1A draw

If you're looking for the source of a 100mA rest current draw, try dis-connecting the front dome light. As previously posted, the seat control modules are one of the most common C-Class battery killers, but in my experience, the dome light is the second most common fault, especially when the rest current is in the neighborhood of 100 mA.

Thanks guys, where is this seat module? Since the majority of fuses are for the seat adjustments. I've just waited 2 hours and the current is still 1.2 A. And the dome light is still buzzing!!!

Who said they don't build them like they used to???

What is the right way to disconnect the dome light?? I've found the connector with 4 browns to it. Disconnect the grounds?

Is there a dome module that goes bad??

Gary

battery drain
 

Without solving the difficult short problem, you can always get a device called "PRIORITY START" . It hooks to battery and monitors voltage draw. If it senses remaining battery voltage level too low, it disconnects battery but still allows a minute volatge draw for locks, etc. Then when you get into car and turn key (or anything calling for voltage) the unit senses the draw and reconnects battery. Away you go. Handy little device so you never get caught with dead battery due to strange drain while parked.

A rest current draw of 1.2A is a good indication that both seat control modules are faulty. I don't know why, but for some reason they seem to fail in pairs, with a current draw of, you guessed it, 1.2 A. They're located beneath the seats.

Strange, been a few days no problems. Took a trip to Santa Barbara w/jumper battery in trunk. So Far, So Good. Mods must be going to sleep correctly.

Battery Drain
 

I had a 210 car with a .02 amp drain and it turned out that the AC blower motor regulator was bad. I checked everything on this car with a fine toothed comb and nothing else was causing the battery drain. I read on a forum in WorldPac that the bad regulator would cause a drain and that was the problem.