You need to read ISN from MSD81 first.
MSX8X family require ignition ON to read ISN, so you have two options:
- Either you read ISN on bench (you can arrange the ignition ON by powering 12V to the ignition PIN)
- Arrange any CAS with a key, when you reach to the DME ISN window, just replace the CAS, switch ignition ON, then read ISN.
Once you finih reading ISN, return the original CAS and go to key learning.