For the past 3 weeks my car has messages flashing on and car reacts than reset

What is your question?

can run for miles with no issues than it starts with bell ringing notifying me that parking assistance is off, ABS messages, stabilitrak not working, traction control on engine light on, transmission shifts poorly than it goes off return to normal for days than starts all over. OnStar reports a control modular is bad. Dealer had car but after 170.00 said It would need to get worst. dealer said their were many error codes OnStar said they would give codes to anyone doing work on car I believe one was 1u