have a 2002 Deville caddy 5.7 L CHECK COOLANT LEVEL light keeps coming on. I had pressure test new water pump new thermostat installed flushed system. Everything checked out fine 2 days later light k

may be there's an air pocket in the system , might be a bleeder near the thermostat housing ,

There is an electric sensor in bottom of expansion tank. In older cars it will stick and give false message. Ignore it, but open tank occasionally to check coolant level--the way we always used to do it before we got fancy.

You CAN remove the expansion tank, flush it out (there may be debris keeping the sensor from operating properly) & then refill. That worked for mine