why is my "check coolant level" displaying across the screen when i have no leak on 2004 Cadillac DeVille

my "check coolant level" was on and i filled the reservoir on 4/1/12 and it went off. i took my car to the shop and they did several pressure tests and said nothing is leaking. i picked my car up on 4/9/12 and the "check coolant level" was on again. i filled it yesterday the warning hasnt come on so far.

1 answer 1 comment
THERE IS A LEAK SOME WHERE CK P/S FLOOR BOARD FOR COOLANT LEAK AT HEATER CORE OR A SMALL HOSE LEAK UNDER MASTER CYL AREA VERY COMMON
wow, that was never mentioned! thanks alot!