Thursday, December 1, 2016

W211: The Most Ridiculous Battery Drain Problem Ever, 2003 E320, P.1

I suppose it's about time I started posting up some of the newer cars I work on, as some of the problems they have may help someone make decisions about moving from an older chassis MB to some of the relatively affordable in purchase newer chassis.

Alright, so with that....

I'm equipped to do anything, so let's see if we can get this one sorted - it's my younger brother's car.... a 2003 E320 (WDBUF65J53A150123) with a hair under 160k miles.

What it does

Battery drains close to dead overnight, needs a quick jump and it's fine for the day. The car had a red battery warning on when it was initially purchased. Two brand new batteries were put in along with much newer and updated battery control module. Red warning hasn't been back, all is well. BUT!!!

If you park the car, remove the key and just sit there without touching anything, there's a whining noise coming from the low center of the dash. The radio cassette/CD player (Audio 50, no nav) system occasionally makes a noise and no matter how long you leave things be, you will always be able to open and close the windows, move the seats, or turn the radio on. Essentially the car never seems to go into it's sleep mode.


Per MB procedure for battery draw, every door was opened with all the door pins taped shut, the hood opened and latches activated shut, and trunk opened and activated shut. As far as the car knows, everythings closed. This let's me get to all 3 fuse boxes on the car, without the car's alarm going ballistic. With my meter between the (-) post and the BCM (battery control module), amp draw with the car not sleeping was around 4 amps and stayed there for about 2 minutes and would then drop. The car will CONSTANTLY fluctuate between 74mA and 1.97 amps. MB manual calls for 60mA being OK, though preferably being 40mA and under at rest. It will fluctuate consistently and evenly between the readings all withing a minute of the variants. Oh Joy.

Proceeding to pull every last fuse and relay in all the fuse boxes has no change on amp draw fluctuation. So there may be either a coding problem on the car from a previously replaced component, a module staying awake, shorting wire, etc... OH JOY...

I've also completely disconnected the alternator from the system, which has no change. Which is nice because the alternator looks to be a fairly recent replacement. Instrument cluster was also disconnected and isolated with no change on draw. OHHH JOYYYYYY.

What's been done

- Both Aux and Main batteries have been replaced with new
- New and updated BCM
- I believe the front SAM has been replaced at some point to chase the problem

Once my scanner get's through it software updates, I'm going to be running the codes and will have an update post with the fault list. I'm going to omit every low voltage oriented code, as those will set off multiple modules from the drain. Should be interesting to get this car sorted.


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