2001 S 500 120k miles
It recently started having some electrical issues. First, the auto-door lock/unlock system and the remote and the trunk opener stopped working.
Next the radio (original) stopped making sound but still turns on and functions otherwise.
Yesterday it went into limp mode and displayed a BAS ESP and Airmatic warnings as well as the Check Engine light went on.
I reset the limp mode and took the car directly to two different auto parts stores where they were unable to pull the codes as apparently the connector under the dashboard isn't getting any power/signal. This morning, all the messages are gone but the check engine light is still on as is the ABS light.
When the door locking system first failed, I checked all the fuses and, in an attempt to open the trunk without the emergency blade key and they were all okay both under the hood and under the back seat. So I followed the instructions online for resetting the system but nothing worked.
Obviously, I've got something serious going on here but am hoping (praying) it might be one thing that can resolve it all. Otherwise I am thinking I may have to take the car to the Mercedes dealer to diagnose the problem as I am well aware that electrical problems can be the hardest to diagnose without all the special training and tools.
Any suggestions on how to approach this problem would be greatly appreciated.
thanks

 

Just picked up my 1999 S500 yesterday, and will be going through what might be a similar unknown drain on my electrical system

Such beautiful cars. I sure hope the following results of many hours of research help you and others

Ordered a scan tool, which apparently has all the dealership functionality including ability to diagnose which module and where drains occur

From amazon it was 180 dollars for:
FOXWELL NT530 for Mercedes Benz 38 Pin - All Systems, All Maintenance Service - Bidirectional Diagnostic Scan Tool OBD2 Scanner Automotive Code Reader ABS Bleed SRS Airbag SAS TPMS TPS EPB Oil Reset

This is what forums indicate we need for dealer level diagnostic scans

I disconnected my battery to place on slow trickle charge before a test, which can be free at most auto parts stores. I believe our cars only function properly with a strong healthy battery.

I am reading about the fall back option of a remote battery disconnect, basically a key fob which disconnects the battery for long term parking, some say this is terrible for the system memories, others indicate they use without trouble as needed for a perfect battery following periods of not driving vehicles like ours.

Enjoy the ride, and let's never use the word stealership
Don

 

How is the Foxwell scanner working? I need something that can talk to the TCM and the BCM.