2002 Cadillac STS Check Colllent level message

Hello,

Did pressure test show a drop in pressure? If not the coolant system is contained and no leakage anywhere.

Have you had any work done to the coolant system prior to the problem starting?

Could also be that the coolant level sensor is going bad.

.

Sometimes a pressure test is better if it can run through a cooling down, like overnight. Is there any evidence(dexcool crust) anywhere on the lower engine. A few things come to mind, leaking coolant pump cover, a leaking coolant pump housing(aka crossover) typically rear bank block seal that can be difficult to see, and a blown head gasket due to pulled threads in the block. Have a block test run, to see if there are any combustion gases in the cooling system to indicate an internal leakage.