How to downgrade BMW CAS3 E90, read ISN from DME and change ISN CAS using CGDI Prog BMW key programmer.
Keep stable power supply.
Step 1: Downgrade CAS3
Select CAS1-3+ Key Match
Read Key Info.
CGDI BMW require to downgrade current CAS versions.
Press Yes to downgrade CAS3.
Downgrade in process. Wait until it reads key information.
Save backup EEPROM bin file
Step 2: Read ISN
Select BMW ISN Read Write function
Read CAS ISN
Read CAS ISN success
Copy and paste the original ISN to text file.
Step 3: Write CAS ISN
Enter the ISN DME you desired to change to CAS ISN area
Press Write CAS ISN
Write CAS ISN successfully.