I have same exact issue on my E90 M3.
I thought it was the starter when it occurred for first time, but it turned out to be CAS module for my case.
Apparently CAS module is known issue for old E9X models according to my mechanic.
You can diagnose your car by unplug ground cable from battery when issue occurs and plug back to see if car starts fine.
If you are lucky, you can resolve this issue by simply unplug CAS module harness and clean them. if this method doesn't work, you have to replace CAS module i believe...
|