Oil level sensor Malfunction

[MrPython]

I just got a '08 bmw 750li with 140k in excellent condition. The oil level sensor warning kept coming on when I shut the car off. I replaced it with a new one and it worked when I started the car the first time it read the level correctly. (I just changed the oil when replacing the sensor)The next time I started the car it was fine until I shut it off and I got the Oil level sensor Malfunction warning and the check engine light was now on. I've reset the oil service before the Idrive but it still doesn't show the correct oil level. I've changed the Alternator put in a new battery and changed the battery cable and still, it's the same problem. Any help would be appreciated.