juanmor40

By any chance, do you have keyless go, or whatever that feature was called back in 2003?

Sister's 2012 ML 350 used to drain the battery, old and new in a night or 2 at most. When she locked it with a double-click, the car went to sleep and everything was OK. If she forgot to lock it, the car was dead in the morning. In her case, she removed the start push-button and uses the key for the start. The battery has been trouble free for 4 + years and counting. Asked her if she wanted to be fixed, and she declined.

You definitely have a drain. If nothing is obvious with the measurements, you can start by bisection of the fuses: remove a set of them, check in the morning. If it is OK put them back, and remove some others from the leftover set. If it drains, only put half of the removed ones, and repeat until 1 left. Brute force but bullet proof.

Good luck. We will be here waiting for your updates.

Plutoe

There is one very important lesson to be learned form post 75 and 76. That is just because your battery drains overnight or over a couple of days do not be brilliant and assume the battery is the fault. Most likely the circuit causing the drain can be found by removing front and rear fuses and with a meter locating the circuit or if you have MB XDOS diagnostics you can quickly find by analyzing the CAN

bigsquid

Hi,

No, my e500 doesn't have the keyless start, but thanks for the suggestion!

Update:
I charged up battery again, back past 12.6v (which it should stabilise at I think) - and have removed all fuses (apart from fuse #8 for alarm) in the rear left fuse box by the CD thing. I've locked up the car with alarm on, and will see what the voltage reading is in the morning again.... at least if it does drop overnight I can (hopefully) rule out anything in fuse box circuits 1-16 (apart from 8).

We did have a brainwave thinking that maybe the interior boot/trunk light was stuck on, so tested for this by leaving my phone recording a video from inside... alas it did turn off instantly on close.

bigsquid

I guess that if I still see voltage drop in the morning I need work out how to test and remove fuse #8 (alarm) without the neighbours complaining.. as that fuse seems to be the one that is set to trigger if the alarm ciruict breaks elsewhere, I guess to prevent people from cutting the wire to silence a break in.

That does leave me thinking about the siren as I did read in another post here, which I now can't find, about someone finding it was actually fuse circuit 9 to be the problem, and had to remove the wire from the back of the box on part of the alarm circuit to fix... also mentioning something about their being a battery actually inside the siren? Not sure. Surely the alarm has some kind of circuit that maps over to the 'other' battery

Anyway - if I have no change in the morning I'll move to a different fuse box I guess!

bigsquid

Couple more notes

Post #71 - Why remove seat modules if they are fused, are they? I'm confused here - if they are fused, what is the advantage to removing them physically rather than testing through removing the fuse?

Post #72 - This is a great theory - tailgate hook - How can I isolate the tailgate hook relay to test this? Which Fuse # is this one? The idea of using heat sig to test is genius. I have a IR camera, so may try this!

FYI I have been using this fuse list:
https://fuse-box.info/mercedes-benz/..._box_diagram-2

juanmor40

also, not a MB, but Ivan is great diagnosing battery drains. Worth watching some of his videos.

bigsquid

Thanks for the videos - oh man I feel for the guy in the 1st vid, saying he has 3 in his shop with the same issue right now and he's still got issues... 12hrs in...
Side not that he replaces the actual fuse boxes themselves, as they were causing issues. Too many variables!

Update from this end.

Manual removal
Removed all fuses from rear (apart from fuse 8, alarm) and then locked car as usual and left overnight, had a charged 13.2v battery when I left it (7pm) and by 9am it was at 12.1v.

FYI Multimeter in series readings (after 15mins)
All fuses IN (rear box): 0.07a - 0.1a in sleep
All fuses OUT except for #8 (alarm) (rear box): 0.07a - 0.1a in sleep
All fuses OUT (rear box): 0.04a - 0.8a in sleep
All fuses IN, and #8 out (rear box): 0.04a - 0.8a in sleep

So I can see from this the alarm is drawing more power here, but in reality everything is still in bounds of MB's 0.02 - 0.08 standard draw.
It makes sense the alarm would draw 'extra'

Next up..
1) Charge up battery again, and then remove all fuses from rear including #8, and then leave overnight to check drain by the morning.
2) If that doesn't work, I guess next I will replace all those fuses in rear, and then take out all fuses in side drivers panel and do the same.

I had this message from someone else, no idea if it's legit as I have not tried these fixes, or whether what he says is even possible in this car, he had a w211

"Yes, I've heard of it, but didn't suffer it on mine. From memory, check things like boot light, interior lights by removing bulbs. Also ensure double locked and try switching off the interior alarm sensor and the anti-tow away alarm sensor (buttons for both on central console). Apparently these cars have so much of this electric/electronic stuff that the batteries have to be in tip top condition. Mine's got a stop-start battery but no s-s."

One day I'll fix this!
Or not, and I'll give up and take it to a specialist and they will find it..

Might get myself an amp clamp to make it easier.
Would be interesting if you can get the amp clamp to log the total amps drawn overnight.

juanmor40

bigsquid

That's a great bit of kit - I was actually looking for a way of logging the total amps overnight, and this is way better than anything I'd seen.

He talks about telematics - my e500 does have a phone inside the holder, and it has an old 3G sim in, so technically we are having 3G phased out here too, so could be an issue perhaps. I think I'll add the phone charger fuse to the list of ones to pull next just to rule it out.

"Fuse 55 (engine compartment) Telephone handset (up to 2007)
Bluetooth module connector (up to 2007)
Portable CTEL separation point
Emergency call system control unit (as of 2007)"

However, at this stage I do know that at 'some point' during the sleep there is some kind of draw, regardless of the known cadence or draw time that this device would show.
Even if I could see this as a 'once every 5 mins it pulls 1amp' kinda thing I'd be no closer in working out what it was.

Super frustrating!

bigsquid

"and try switching off the interior alarm sensor and the anti-tow away alarm sensor (buttons for both on central console)."

So I located the buttons in the roof centre console, and pressed the buttons.
The left (interior sensor) just blinked once, and the right (tailgate) multi blinked...
I watched a vid on this, and in his video BOTH blinked rapidly - is mine showing a fault then?

Can someone verify this for me on theirs please?
So basically turn off your sensors from your console and see whether they both blink rapidly, or if one just single blinks.

Will be interesting if you come back to me and say that they both blink - as this perhaps could suggest something that is at fault with my sensor perhaps

One more thing - the SOS function, I assume this just triggers the mounted phone's emergency call, I'm sure there is no actual telematics inside the e500 w211 right?!

Also - I removed all fuses in the side panel drivers side, and check draw again, and stable flow of 0.05a - 0.08 spike, so again within bounds.

Going crazy over here.