I've been trying to hunt down my battery drain for months on my E55, and I can't seem to figure it out. I seemed to have narrowed it down to the CD changer and stereo fuse and audio gateway fuses drawing a large amount of current after the car goes to sleep (waited 15 min before testing each fuse for draws by measuring voltage drop at the fuse). The weird part is, even if I unplug all the 3 fuses, it still draws. I noticed the stereo/radio doesn't turn off after removing the key and opening the door. It used to, but not anymore.

I used a fiber optic bypass tester loop, and the radio still stays on and still draws even after bypassing the navigation unit, the teleaid module, the sirius XM satelite radio moduel, and the CD changer (one by one since I only have one fiber optic loop), which seems to leave the head unit and the audio gateway. I tried unplugging the head unit (can't connect fiber optic tester loop to the head unit connector since it doesn't have just the fiber optic wires going to it), and it still draws. I also tried to communicate with my Autel scanner, and none of the audio gateway modules communicate with the scanner. So I bought 3 different used audio gateway modules off of seemingly reputable sellers on eBay (most of them had a physical locations too, although dismantlers aren't always very honest), and none of them communicated with my scanner except for the one with a different part number. When it communicates with it, it says "Diagnose" on the head unit, and my scanner can communicate with it, and I can see that it came from a car without navigation or teleaid or satellite radio. But even with that one AGW module, the radio still stays on after removing the key and opening the door, and the car still has a battery drain. I don't have anyone with a STAR scanner so I can't program that AGW module to see if that will fix it. Do you think the other 2 AGWs I bought were bad? Or maybe my Autel just doesn't communicate with the older AGWs? The newer part number AGW I bought is from a 2007 E320.

I have noticed the CD changer doesn't open anymore since the battery drain started, and also the rear dome light doesn't turn on anymore, even though the rear reading lights still turn on. Also the whole week before the battery drain started, I was hearing a weird noise from the dash or engine bay, sounded like the CD changer trying to load a CD or trying to open, but I also have a Secondary Air Injection Pump code, so not sure if it could be that. At one point I thought it may be the rear SAM causing the drain? I forgot what I did, but I thought I ruled that out, but I'm not sure now since it's been so long I've been trying to hunt down the drain.

Anyone have any suggestions? I'm pretty stumped.

 

Another way to find battery drains:

 

not sure if you solved your issue. after 8 years found mine. it was the GPS navigation drive. maybe it was due to me having a DVD copy versus an authentic, but the drive would seem to light up every 5 secconds. seems it was keeping the MOST or CANBUS network alive. new car battery wouldn't make it 1-2 weeks. now i can go 4 weeks without an issue. haven't tried longer yet, but no doubt i'm good as gravy now.

 

1. Buy or borrow a clamp-on ac/dc ammeter such as a Klein CL390 (it must be able to measure dc current).
2. Clamp it around the battery's red cable.
3. Access each of the car's fuse blocks one at a time.
4. Close all the doors and wait for the car to enter standby (all lights extinguished).
5. Have a helper read the ammeter while you remove each fuse to check if the battery drain is on that fuse's circuit.
6. If the pulled fuse has no affect, replace it, and move onto the next fuse.
7. Continue until all fuses on all fuse blocks have beeen checked.
8. Once the circuit has been identified by fuse, check all devices on that circuit, especially add on devices, by disconnecting them. Finding them and their connectors might require access to.MB WIS/ASRA.
Apologies if you've already done this.

 

A lot of information to digest @TheShiekh .

I also had a power drain issue on my CLS55, to be honest I am not sure what I exactly did to solve it, but its highly strange that you cannot access the AGW with your Autel. I also have an Autel and was able to access it and code it where necessary. Some things:

-I also changed my alarm siren/horn. It wasn't working properly anymore and is a known culprit for power drain
-The CD changer needs to be connected with the power cables, else the headunit wont turn on. You can test this easily by drawing the fuse for the CD changer
-If you disconnect MOST components, you also need to adjust the coding for it. Else the AGW will expect the component to be there
-I also removed my phone + cradle in the arm rest. It always felt warm, meaning it was using power.
-I also replaced the BCM with the newest revision (I bought a 2nd hand from a 2007 E-class)
-I also replaced the AUX battery relay under the scuttle. If the AUX battery isnt charged properly, then it will keep asking for power from main battery if I am not mistaken
-I disabled the Interior Motion Sensor for the time being
-I serviced all (or almost all) earth points in the car, removing any corrosion and scuffing them up

Do you also know if your alternator/voltage regulator is working properly?

 

Electrical gremlins ... a category that never ends with these cars/motors. You can literally swap every item talked about in this thread, two months later something else will come up. You can't fight AMG electrical issues, they ALWAYS win in the end...

Good Luck, OP.