Sometimes BMW CAS3+ eeprom data is corrupted after bad reflash/downgrading and there is no communication with it and no ignition on car. Many devices will kill CAS3+ when downgrading via OBD, Xhorse VVDI2, Yanhua ACDP, IM608, AVDI even Autohex II without a sufficient power supply.
No need to make backup, even if something happened OBD without backup you can repair it in hextag.
How do I recover data/restore with Hexprog? What is the procedure to repair CAS corruption? under what option?
Hextag has an option for this can change from programming mode to normal mode probably happens when downgrades fail. You can read eeprom and check CAS in programming mode or normal mode. edit option in eeprom and you need to write another flash also.
If you have autohex you can check on it first if can solve it OBD itself. When it comes to Hextag you can check from edit option in EEPROM if CAS in programming mode or normal mode. If in programming change it to normal and write eeprom back. Also you need to change Flash.
Try to recover the original CAS with following steps:
Find good flash file from same part number CAS. Write it to CAS using hexprog.
Read original eeprom, change line 0F90 (first three columns) to DA AA 55, write back.
Perform individual programming (using key programmer on bench).
CAS should be alive after this.
These step should bring the CAS back to life. Now you can learn new key (sometimes you don’t need DME ISN) but it may ask you for ISN which autohex ii and some other devices can extract DME ISN for you.
With HEXTAG, successfully repaired a corrupted CAS 3+ after a bad ISTA/P update.