Thank for the reply!
Today I borrowed a BSM from a friend. Not the same engine, V6 3.0, but it was the same BSM, the same number (BSM L04-00).
I installed it and the car started !! Wow!
I tried "my" BSM in his car and it did not start.
When I put "my" BSM in "my" car again, has not been started.
I am now convinced that there is something in the BSM is wrong.
But my question remains. Can I install a brand new BSM without programming?
The price difference between a new and a used is not so great.
I'll call a Citroën dealer tomorrow and ask and order one.