Hi guys, so that's what happened to my OM646 W204
Firstly the fan inside the car would stop and go whenever it wanted, so we did service it and seemingly it was all good.
Then what happened is that when I flashed my headlights to signal another vehicle my ABS light went on for a bit saying the ABS is inactive but then it disappeared.
Then the next day the fan inside stopped working again. Afterwards I left the car for a few hours and when I came back and inserted the key, all possible malfunction lights showed up on the dashboard. The car would start, but the stick would not go from P mode to gear (D). I had to release it with the emergency button under the stick cover to get going but the car was in emergency mode - gears would stay at minimum (5000 RPM at 70 km/h) and nothing worked (blinkers, speedometer, almost nothing). I finally left it home and the next day removed the battery for a few minutes and re attached the SAM module power plug. First the car would not start at all, all lights black. Then I removed the battery and after that the car worked, no errors showing up except for check engine light. I managed to get into service mode and got some error codes. Then went to a shop to get it diagnosed and the guy said it's most probably the Alternator - it would need to get serviced as it doesn't bring enough power to the components and the car shuts them down. He also put some contact spray on the ABS sensor. Now the car seems to work with no errors, fan works. However when when in service menu it shows that HU Supply Voltage is 12,5v and the battery voltage is 13,8. Also when I started the car in the morning HU Supply voltage was 10,5 V. What do you think? Car mileage is 318 000 km. Here are the error codes I got :
01-4c-19002
01-4c-20780
01-4c-08106
01-4c-1B204
Here are pictures of the HU Supply voltage

 

"Then went to a shop to get it diagnosed and the guy said it's most probably the Alternator."

What did the shop do? It probably needs a new alternator.