Takk gutter. Det ser ut som e34_525tds har helt rett, og det er jo gledelig, for det betyr at man smekker på hva som helst, putte nøkkeldingsen i slotten sin, inn på iDriven og resette.  
Fant en tråd på babybmw.net om samme tema: http://www.babybmw.net/forum/viewtopic. ... 36&start=0 
"Older runflat systems used wheel sensors but current 1 series don't. It's all done as stated earlier by the abs system being used to monitor wheel rotation speeds. A deflating tyre will rotate faster as it's radius reduces." 
"Earlier cars (like E46's) has these things but the batteries wear out and they become unreliable (and sometimes fall off!). 
That's why the newer stuff (E87, 81, 90, 92, etc.) uses wheel speed as a (very effective!) reduced pressure warning (the wheel with less pressure spins faster)."