Similar story here for me, 06 550i
Last night, when I started my car I got a "coolant too low" warning on the iDrive. I had some in the trunk because I heard this could be a common thing, so I immediately turned off the car and added the coolant. Checked it again this morning before I left for work and it was full. On the drive in (15 miles?), my Service Engine Soon light came on, but there were no codes in the iDrive and everythign shows it checks out fine. Shouldn't it show in iDrive, or am I wrong there? it seems to run fine - maybe a bit rough when I'm not giving it gas but that's about it.