This is a Z3 coupé 3.0i model 2002.
The driver's seat is stuck at mid heigth. Impossible to move it neither up
nor down.
I used an articulated mirror to see what was happening beneath.
The screw goes through a nut mounted in an U-shapped Zamac piece pulling a
lever. Behind the nut is a crimped washer slighly larger than the
screw, crimped on it, preventing the screw to come out of the nut. The coin
is there,
between the washer and the bottom of the receptacle.
Go figure how this f.cking coin ended here !

I found a link explaining the removal procedure:
http://www.waycoolinc.com/z3/02/100602/shish01.html

Although I'm not a neebie, I've to admitt that this is the first time I have
to operate on
protection systems. I assume that there's a pyro needing to be disconnected.
How to ?
If I need to disconnect the battery, what are the precautions ? How long may
it be disconnected without any trouble ?

I read about some warnings concerning the airbags and belt tensiometers.
That's rather vague or general and not directly related to my Z3.
What are the precautions to take in order not to trig errors inside the
fault memory ?

TIA