Ihave the same problem with my C320. I parked the car and went canoeing for three days and when I got back, dead battery. I had recently purchased a new battery three months earlier from the dealer so I ran some tests on the battery and it was pretty much dead, it would not hold a charge so i brought it back to the dealer and they refused to honour the warranty. I explained my symptoms to the warranty manager and they still refused to honour it, they wanted to inspect the car first. Well based on whatI now know, I know why, they knew what was wrong and did not want to admit it.
To diagnose the problemI downloaded the control schematics for the C A N . This is the communications network in our cars that allows the various control devices to communicate.Its similar to the ethernet network for your computers at work or home. Each device, like theseatcontrols in the doors and the power seats, are connected to a network.Older carsconnectedthe devices together, (i.ewindow switch to window motor)however now they are all connected to a two wire network. The ESI is the network controller. When the ESI andall the other controllers on the network are poweredup theyconsume between 1 and 1.5 amps, @12V thats about 12-18 watts of power. When you turn off the ignition the ESI waits 45 seconds then goes into sleep mode. It thenconsumes about 200mAmps or .2 of an amp. This is to allow the keyless entry to function. When youpush the key the ESI wakesup the network andthen you canunlock thedoors, windows, sunroof, move the seats, the steering column etc. If you then do nothing for 45 seconds it again goes back to sleep.
In order for the ESI to sleep all the controllers(seats, windows, sunroof, etc.) must stop communicating with it(i.e. the user must stop pushing the buttons). In my case, andI suspect in most of the other cases the seat controllers continue to chat with the ESI module prevent it from sleeping.They donot actually drain any power, they just prevent the car from sleeping.
Lets do some math,if the car used 1 ampfor12 hours it will consume 12 amphrs. The batteryis a 100 amphr battery so it will be drained down to 88%. At 88% the car will start fine. If you leave the car for 3 days it will drain 72 amphrs and the battery will be at 28%. Since these are not deep cycle batteries your car won't start. If you drain the battery down to 88% each night it will spend most of its life below 100% which will cause sulfation and ruin the battery. You will loose about 10 % capacity permonth. So you put in a new battery, it works for three months then you leave your car for 24 hours. The car won't start.
If the car goes to sleep it drains 200mAmps, which in 12 hours drains 2.4amphrs or the battery drops to 97.6%. The car starts, the alternator charges it back up and you get minimal sulfation.
The problem is pretty simple for mercedes shop to figure out, you put a amp tester on the battery and watch the car go to sleep. However figuring out which module is causing the chatter can be challenging, i suspect the dealers cannot inspect the traffic on the CAN so they have to guess which controller is the culprit.
You can try this at home,
1. with the car OFF disconnect the ground wire to the battery and insert a 10amp current tester, (CAUTION) donot try to start the car or you will need a new amp tester.
2. you should see a current between 1 and 1.4amps. When you first connect the power the ESI will wake up. Close all the doors and wait for 45 seconds, you will notice the driver's commandconsole illuminationinside the car will go out and the current will drop to 200mAmps.
3. If you open a door, or push on the key the current will jump to 1 Amp again as the ESI module wakes up.Rinse and repeat....

If you are having this problem the current will not drop, and more then 200-300 mAmps will be a problem. Simply disconnect the various modules, I would start with the seat controllers and then wait 45 seconds after you shut the door to see the current drop. In my case it only went to sleep whenI disconnected both seat controller modules. OnceI did that the car went to sleep every time. So the problem is either the ESI module, the seat controls on the doors, or the seat control modules on the floor. You cannot be sure which one it is becauseany module can keep the car awake.

If you only have a volt meter then use this test( it is not as good a test):
With the car turned off attach the volt meter to the battery posts. You shouldmeasure between 12.6 and 12.8 volts. Open the door and confirm the command console is lit. Then shut the door and watch the volt meter. It should drop slowlyby .1 or .2 volts. The voltagedrop is caused by the ESI being awake. After 45 seconds it should start to rise back upand stopbetween 12.75 and 12.8. If it doesn't rise but continues to drop then you have the problem.
You can repeat this test whiledisconnecting modules until the voltage bounces back up. This test assumes you have a good battery and alternator, the previous inline current test doesn't care.

What Mercedes should do is a software upgrade that times how long it remains awake while the ignition is off and either raise an alarm, heck it alarms for everythingelse,or force itself to sleep. It should also monitor the battery voltageand alarm ifthe battery drops below 80%. This would cost them almost nothing and save alot of their customers grief.

If you have any questions or would like to contactme,Ican be reached at:

Steven Ladouceur P.Eng.
steven.ladouceur@terralock.ca

 

Those prices don't sound out of line.
The trouble is that we are still having trouble getting used to these electronic nightmares we call cars.
We want all the technology we can get but we forget that the more complex these contraptions get the more there is to break and the more we need the electronic test computers to diagnose needed repairs.
I have long said, give me breaker point ingnition and a carburator and I can fix it under the tree.
Those days are long gone now NASA has trouble fixing these space shuttles.

Meanwhile. F1Fan you wrote<<But at least you can tell the MB tech to fix one prob only (and save on the hourly charges) rather than have him diagnose the entire car.>>
Actually if you tell your service advisor why there are multiple error messages ie you disconnected the battery and he annotates it on the repair order the technician will simply reset the messages and rerun the diagnostic proceedure to find the true defect. Flatrate Technicians usually don't want to waste their time running down rabbit trails while one of the other Techs gets all the "gravy work".

 

I have an 01 C320, is there anyways you can disconnect the battery in order to get some of the warning lights to go out instead of going to a MB dealership? I had my brakes replaced and NOW the brake light sensors are on when they were never on before? Any ideas? What is the ESP warning light an indication of?
Thanks

 

If the light is on, either the sensor was not replaced as is required once it shorts out and lights the instrument panel warning, or the new sensor is not properly connected.

If I recall correctly, you cannot re-use the sensor, it must be replaced.

DFS

 

I have a 2 year old battery in my 2001 C320 (71K miles), drove it 2 days ago, went to get in it today and the key unlock would not work. I used the valet key, got in the car and inserted the key into the steering lock......nothing. No lights, nothing. What could be wrong? Sounds like more that a battery.

 

ALARM WENT OFF AND I TRIED TO CUT IT OFF WITH THE REMOTE FOUND OUT, IT WAS THE BATTERIES IN THE REMOTE, AND THEN ,I TRIED TO JUMP IT AND BATTERY IS COMPLETELY DEAD. WHAT DO I DO THIS IS A NEW BATTERY?

 

yes,all i did was unplug my seat problem solved!