The car kit says "Power off' if it does not connect to any device for 2 mins. When you get into the car, it should say "power on" and "CONNECTED". and then it will stay on.
If it only says 'power on', but NO 'CONNECTED', then it indicates the car kit is NOT connected with your phone. It will auto power off after 2 min.
In this case, please make sure your phone Bluetooth is on, and CLICK ONCE on the car kit volume knob and it will re-connect to your phone. You will hear it says 'connected' NO need to re-pair them.
Also sometimes low battery could cause this issue. Pls remember to charge your car kit.
If this does not solve the problem, pls contact firstname.lastname@example.org