The vehicle must be on a level surface when checking the coolant level.
It is normal to see coolant moving in the upper coolant hose return line when the engine is running.
Check to see if coolant is visible in the coolant surge tank. If the coolant inside the coolant surge tank is boiling, do not do anything else until it cools down.

If coolant is visible but the coolant level is not at or above the mark pointed to, add a 50/50 mixture of clean drinkable water and DEX-COOL coolant.
Be sure the cooling system is cool before this is done.
What to Use
How to Add Coolant to the Coolant Surge TankOnStar Overview
Voice Command Button
Blue OnStar Button
Emergency Button
This vehicle may be equipped with a comprehensive, in-vehicle system that can
connect to a live OnStar Advisor for Emergency, Security, Navigation, Connection,
and Diagnostic Services. OnStar services may require a paid subscripti ...
Braking
Braking action involves perception time and reaction time. Deciding to push the
brake pedal is perception time. Actually doing it is reaction time.
Average driver reaction time is about three-quarters of a second. In that time,
a vehicle moving at 100 km/h (60 mph) travels 20m (66 ft), which co ...
Brakes
Disc brake pads have built-in wear indicators that make a high-pitched warning
sound when the brake pads are worn and new pads are needed.
The sound can come and go or be heard all the time when the vehicle is moving,
except when applying the brake pedal firmly.
Warning
The brake wear warning ...