Re: 159 1.9jtdm - No Oil In Engine Message
It sounds like the engine has stalled, or not started properly in the first 2 examples you gave.
A number of people (including me) have had the "bag of nails" running occasionally. It's almost as though the car is running on 2 cylinders.
Perhaps the oil pressure sensor is being over sensitive, and can not deal with a stalled or not quite starting engine.
I know that if I stall my 1.9D, then I sometimes get a message about low oil pressure (can't remember the exact words). It just means it has stalled.