Computer Bus Voltage

What is your question?

It doesn't start or shutdown with one push of the button, I think all my problems are caused by voltage spikes on the computer bus Had it into two dealers, I think the computer voltage should be regulated below 11 volts to prevent spikes as the alternator/battery bus jumps all over the place from 12 to 15.5 But I can't get them to provide me with test results or requirements.

What makes this problem better or worse?

Random but I think it is happening because I'm doing other things at the same time seatbelt etc.

How long has your 2021 Cadillac XT5 had this problem?

Since I bout it in April