What codes did you get? I had a non-responsive module when I turned the ignition on without an airbag connected and then I could not get the air bag light to clear. Being a Z3 owner as well, I had come across this thread:

https://www.bimmerforums.com/forum/s...ly-found-a-fix!

Abel has figured out how to fix some of these modules, including early E53s (you’ll have to message him to see if he can do yours). He did mine, but the problem was still present when I reconnected it and tried communicating with it. Abel then walked me through coding a module pulled from another car and that worked for me.

I would start with what was already suggested in this thread. Determine the exact part number of your module. Part numbers change mid-cycle, so using RealOEM or putting eyes on the unit are required. Then contact Abel.