What was found
AFTER DEICING IN THE GATE UNDER APU POWER, MAIN DECK CARGO SMOKE WARNING FROM AFT SENSOR MOVED FWD TO BOTH MID SECTIONS. MAIN CARGO COMPARTMENT FILLED WITH SMOKE. EMER EGRESS ACCOMPLISHED. INSP CARGO AREA WITH NO FAULTS FOUND, RAN APU & ENGS IAW JRH & HAD NO SMOKE. ACFT WAS JUST DEICED, SUSPECT FLUID IN SYS. ACFT OK FOR FLIGHT. PERFORMED CARGO SMOKE ALL SYS PASSED.