The original DME sustained water damage and no longer communicates. My customer purchased a used module. Both the original and the used replacement are MSD85.3, but with different part numbers. I read the ISN from the replacement DME and tried to write it to the CAS module (CAS3++) with my Autel IM508S and XP400 Pro. The Autel said the procedure was successful, but the vehicle would not start. Codes 002F49 (Immobilizer anti-tampering protection) and 002F4D (DME locking), were set in the DME no matter what I did.

I subsequently used the IM508S to read the ISN from the CAS while it was installed on the vehicle, and got a number different from the ISN that I had tried to write to it (so maybe the write with the Autel equipment didn't work?). I assume that is the ISN from the original DME. I tried using Hexprog II to write that ISN to the donor DME flash, which seemed to work, but I started to see intermittent loss of communication with the donor DME while it was attached to the vehicle. I successfully restored the backup of the DME flash and read the ISN from the DME with Hexprog II. As expected, it reported the original ISN of that DME. Immediately after that, the donor DME completely stopped communicating. I cannot communicate with it using Hexprog II, nor with a scan tool, regardless of whether it is on the bench or installed in the vehicle. I'm not sure where to go from here. Can you help?