As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER TAKEOFF, THE CREW NOTICED 'LANDING GEAR INOP' AND 'L GEAR DOOR' ANNUNCIATOR LIGHTS WERE ON. THE GEAR DOOR WAS VISUALLY CONFIRMED AS BEING OPEN AND THE CREW RETURNED FOR LANDING. MAINTENANCE DETERMINED THE PROBLEM TO LIE WITH THE PROXIMITY SENSOR ELECTRONIC UNIT AND REPLACED IT. THE SUBJECT UNIT HAD BEEN REPAIRED 1,420 HOURS PREVIOUSLY.