Low coolant light comes on. Just added coolant last week. No signs of leaking
on 2003 Hummer H2

What could be wrong?

Asked by for the 2003 Hummer H2
Keep an eye on your coolant level. If it continues to loose coolant, and there is no evidence of external leakage, have the system pressure tested. Its possible the engine has developed and internal leak and the coolant may be leaking into a cylinder, or the oiling system (pan/galley).