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I have a 2007 C350 Luxury model that is experiencing battery drain issues. I am at a loss as to what is causing the issue and I have spent many hours trying to diagnose it. I hope that someone here has an angle that I have not tried yet. I will go over what I have done so far which may take a bit of space.
I have replaced the battery 3 times; 2 new batteries were killed by the drain within 2 days. Then I bought the most durable (expensive) battery that I could find and installed a trickle charger to maintain it as a stop gap measure. This is working to make the car usable but it is not a permanent fix.
I then checked the alternator to make sure it was not over or under charging the system resulting in either battery death or drain, this was fine.
I then moved on to conventional batter drain trouble shooting methods. Using both a clamp on DC current meter and then installing a current meter between the battery and the pos terminal I proceeded to pull out every fuse and relay that I could locate within the car. This included all three locations in a C class vehicle. Nothing changed the current drain during this procedure. To be sure everything should be asleep I redid this many times waiting up to an hour after shutdown. I may have worn out the contact on the fuses pulling and replacing them so many times. I also pulled the power leads to both seat control units because this is a common problem in a C class vehicles with current drain.
I was able to narrow down the majority of current drain to the main wire leaving the buss and going to the front SAM unit-fuse box. I say the majority because car seems to be drawing current everywhere to some degree. With this development I moved on to my code reader focusing on the front SAM.
The code reader produces mixed results, I knew the mirror turn signals are messed which is the front SAM, also the progressive steering is messed up which I think is the front SAM, but I also found issues with other things. There seems to be confusion on the can bus from time to time which is not abnormal and usually can be ignored, but I did find issues with the rear SAM which confuses me a bit. When looking at the live data stream the rear SAM is confused about which door I open when testing. I am not sure what this means but it may lead to a condition of the car never going to sleep.
Other possibly unrelated issues are: the Nav unit makes a slight noise all of the time, it seems to be looking at the disk. It may however not be the Nav unit but the small fan that samples the cabin air not shutting off, hard to tell. As mentioned, the mirror turn signals are intermittent working sometimes and not others. The progressive steering seems to be not working properly making it hard to turn the wheel when stopped, and of course the confused rear SAM.
When I bought the car it seemed to have had extensive work done to the interior of the car, is it possible to have installed the incorrect door module and if so could that cause my problems?
If anyone has any suggestions, I would greatly appreciate them.
Does your car have full power control memory position seats? If so, it might be the seat controller. There is a cheap way to fix it where you change the wiring so the seat controller is only powered with the ignition switched on.
Thanks for the advice, I unplugged the two units during my marathon fuse pulling sessions to make sure that they were not drawing the power. It is possible that I misidentified the units and unplugged something else but this does not explain the confusion in the rear SAM unit (or maybe it does). The inside of the car had fingerprints all over it like someone removed almost all of the interior covers looking for something, my guess is this is what they were chasing. I think that I will try to identify all of the door controllers to make sure they are the correct ones, they may have replaced one of them incorrectly.
I know one place many mechanics go to on the w203/
and other similar vintage models is the wire loom tray below the parking brake pedal.
Along the left wall, under the carpet lies a treasure trove of connectors - and unfortunately sometimes water. Or a disconnect. Etc.
I’m not saying it is there, but you haven’t listed that location. I’m glad to hear your front SAM isn’t / doesn’t appear to have been flooded. (Fall is here, check those drains!)
Take a look.
FWIW. My over head console sniffer fan and COMAND fan both run for a minute or two before powering off.
I pulled the drivers side front carpet to gain access to the wire harness underneath, I wiggled the connectors that I found and checked the condition of the cavity. The cavity was in good dry condition and the connectors were not corroded so I do not think that this is the cause of the problems.
I then hooked up the code reader again and tracked down a few issues. I again found that the Rear SAM incorrectly identifies which door is open, it also can not communicate with the overhead control unit. When I checked the overhead control unit it could not identify that the front doors were open, and it also said that it could not communicate with the Rear SAM. The question is, which unit actually looks at the door contacts? Does the Rear unit read the contacts and then relay the information to the overhead control unit or is it the other way around? This could be helpful in tracking down the problem.
During all of this the car was connected to outside power to make sure that there was sufficient current available to the control units to avoid low voltage and incorrect data.
Again, thank you for the info, it is enormously helpful.
10-29-2019, 07:59 PM
