As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFT CARGO SMOKE WARNING ON AT FLIGHT LEVEL 270 ON CLIMB. RETURNED TO AIRPORT. AIRCRAFT GROUND RUN BOTH ENGINES FOR 15 MINUTED. AIR CONDITIONING CHECKED AT IDLE, LOW AND MEDIUM POWER. ALL VENTS OPENED AND SYSTEM PURGED TO CLEAR CONTAMINATION CAUSED BY GROUND START UNIT THAT HAD BEEN LEAKING OIL ON ENGINE STARTUP. SMOKE DETECTION MESSAGE CLEARED, AIRCRAFT SERVICEABLE.