I disconnected my battery last night so I could replace the fuel pump this morning. After I did the job, started the engine and park assist off message showed. Also radio doesn't turn on, as well as no sound for turn signals or rear hatch tone. Tried to find a cure online but no luck.

 

A full, all 4 code family scan tool is needed to work on modern GM vehicles, or any brand for that matter. Scan is step one with any issues. Scan tool is more important than hand tools today.
GM uses 4 code families, P, U, C and B.