Significant parasitic current draw - PeachParts Mercedes-Benz Forum

spark3542 · #1 12-14-2022, 10:16 AM

Troubleshooting a current draw that is getting worse. Im measuring about 4A steady state. Ive pulled literally every fuse one at a time at all 3 fuseboxes without any change to current draw. I pulled every relay as well. That led me to believe bcm in the trunk is the culprit. I swapped bcm’s with another cdi, but the problem did not switch cars…battery dead as a doornail this morning. Ive also unplugged seat modules. Any ideas on this one? 2005 e320cdi with 401k miles

Sugar Bear · #2 12-14-2022, 10:27 AM

Unplug the alternator and retest. Good luck!!!

dieselbenz1 · #3 12-14-2022, 11:32 AM

I have the same car and had the same problem. It was a steep learning curve to find the culprit component. In my case it was the gateway control trunk fuse no. 6. My friend again with the same car has similar issues but was in the overhead unit by the mirror and a seat control module. Good luck soon you will really be using a multimeter to track it. Took me 2 weeks to find mine and my friend over a year he had a spare battery in the trunk to boost off.

Diesel911 · #4 12-14-2022, 11:38 AM

I did not like the guys persona in this vid but he puts out the info in a logical and effective manner.
I knew how to do it but watched the whole thing and I did learn that vehicles can have more than one fuse box which I did not know.

How to Test and Find a Parasitic Battery Drain (Key Off)
https://www.youtube.com/watch?v=zdIKNnwEjIs

spark3542 · #5 12-14-2022, 03:34 PM

D911, good thorough vid. I had done basically the exact process he laid out, also letting the car go back to sleep when i opened a door.

DB1, fuse 6 had given me problems years ago, and has been removed for some time (yes, no radio).

SB, good point on alternator…its about the only non-fused electrical item. Ill try that next.

Thanks all for the responses!

dieselbenz1 · #6 12-14-2022, 07:59 PM

Only problem with the video is the w211 may wake up the ECU so best to wait till it sleeps again or measure voltage drop across the fuse.
https://youtu.be/8c43Ix6Lf2c

jay_bob · #7 12-15-2022, 06:35 AM

Yep just figured this out for a friend's 2007 W211 yesterday. Pulling fuses causes things to reboot so you have to do the millivolt method across the fuses. Having a GOOD meter and sharp pointed probes are essential for this, you need SOLID contact to the bits on top of the fuses.

Steady state drain on a 211 (measured in series with battery -) should be around 100 mA. Confirmed with my son's 2008 W211 which happened to be here with me at home (oil cooler seal job incoming).

With all the computers awake, key off, you have about 30 seconds of 5-6 A and then it starts dropping. It takes about 2 minutes to get back down to 100 mA.

Trip the trunk lock with a screwdriver shaft (don't forget to reset it by using the normal trunk opener before shutting the trunk). The doors are regular plunger switches so use a clamp to keep them pushed in. And turn the dome light off on the overhead console. ADDED: turn off Bluetooth on your phone to keep it from reconnecting and waking up the entertainment system.

I also had hooked him up to Xentry and he had 9 pages of codes when printed out. I cleared everything and that actually helped more than anything. I think he had some modules that were so upset they didn't know how to go to sleep and were staying awake.

He does have some issues, cam position errors (gas engine eww), heated seats not working, cabin temp sensor by the key switch fault, bunch of little things.

ROLLGUY · #8 12-19-2022, 11:58 PM

My niece's '05 CDI was draining the battery overnight as well. I replaced the BCM, and unplugged the passenger seat module first. No change. I tried the millivolt method across the fuses with all the door and trunk latches tripped, and no measurable draw on any fuses (all three fuse panels checked). The only thing left was the alternator, so I replaced it. Problem solved!!! I got a factory rebuilt one for $315. It was in a new Bosch carton, and looked new.