Can anyone help me understand the concept of Secretkey that appears in CAS4 and FEM / BDC?
Usually devices like Autohex do everything for us, but I would like to understand what SK is for.
Last time I changed ISN to CAS4 with Hextag and added a new key I lost ignition.
It is the same in FEM / BDC where there are SK, ISN DME / DDE and ISN long which are completely different.

Can anyone help me understand the concept of Secretkey that appears in CAS4 and FEM / BDC?
Usually devices like Autohex do everything for us, but I would like to understand what SK is for.
Last time I changed ISN to CAS4 with Hextag and added a new key I lost ignition.
It is the same in FEM / BDC where there are SK, ISN DME / DDE and ISN long which are completely different.

secret key on cas4/4+ is different from ISN it is not the stored ISN. I guess you are using different to identify FEM because in our software there is no option like secret key for FEM/BDC. You have only secret file which you will get after unlock FEM/BDC or CAS which you can use for functions like programming key, edit ISN, change VIN etc.
https://www.microtronik....ns/fem-and-bdc-unlocking