I was sure I had it figured out. Battery voltage was dropping to 11.8v overnight. After going through all the major culprits, I found a 3+ amp drain that went away when I pulled fuse 64, for the COMAND head unit. Without that fuse, the battery would hold at 12.4 ish for 5 days. I went ahead and jumped a wire from the cigar lighter fuse over to the load size of 64, which gives me radio back by effectively moving the power over to the 15R circuit, which is off when the key is.

Battery has been holding fine, until one day I parked the car on the open, upper deck of our parking structure, vs. a couple of floors lower, which is under cover. Battery went down to 11.8v in under 24 hours. Recharged battery, drove car for about an hours, put it back in the covered spot, and it held 12.4 for 5 days. Parked it on the top floor again, and again, down to 11.8v in under 24 hours. Recharged, drove it again, and put it back on the lower level 24 hours ago, and it is holding at 12.4v.

So it would appear that I have something else that is either powering up, waking the CAN BUS, or some combination thereof. Since the only change (other than about 30 ft of altitude) is being open to the sky. I'm thinking either something to do with the light sensor, or maybe the Tele Aid (being able to see the sky for GPS, or get cell signal, or something).

I looks like fuse 40 in the cabin feeds the tele aid, so I'm going to try pulling that. It also appears that leaving it pulled will give me a malfunction light(s), but I'm not sure if being pulled while the vehicle is stationary and not running will cause any issue...thoughts?

Not sure how to approach the light sensor, but that one seems less likely, as I only see that changing state once, when it gets dark, and if that starts the process, it would mean that the battery is draining in something more like 12 hours, which seems excessive.

No codes related to either system are present on the dash or via scanner.

Any other thoughts are welcomed

Toby

The tele aid is on the MOST loop, so is a good shout as may be getting a signal and waking the MOST system up. To bypass it without message you can delete it using STAR SDS and put a fibre link on the MOST cable

 

Thanks for this...I have read a few posts along these lines. If I unplug the module, and install a fiber loop to test my theory, before getting the SDS delete done, will I have any other issues than the malfunction indicator?

Now for my next dumb question...where is the Tele Aid module in my convertible? I've read that it is in the trunk, the console, under the seat...

Toby

 

I believe the teleaid is part of the most system, it is definitely in the r230 and w211, as well as others. Removing it requires looping the most cable around the unit. I would also check your alarm siren, these have been known to cause a large drain. On all of my mercedes of this era, the siren has failed and drained the battery. The w211 e55 I have had a drain that was caused by the amplifier not turning off.

 

Whether its on the MOST, or not, if it's trying to phone home, or something like that, it has to be using power. Once I figure out where it is, I will see what it takes to disconnect it...

And I already eliminated the alarm siren, along with the seat modules, AC, and a whole bunch of other stuff.

 

Another document about rain/light sensors.

A diagnostic scanner may help to test if it works, but wont help with if it causes power drain.

 

Well, looks like it's back to the ammeter...

For over a month, since I moved the COMAND power over to the 15R circuit, the car could sit for days at a time, without the battery dropping below 12.4v, as long as it was parked in the covered space.

Drove it yesterday afternoon, parked in the covered space, and the battery has dropped to 11.9v this morning.

Almost a love / hate thing...I really do love the car, and fortunately, the BatteryBrain makes this much less of an issue...but I sure hope I can sort it out.

Since it seems to be a moving target, I'm wondering if a larger component, like the front SAM could be the culprit.


Toby