As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT 434 - AFTER TAKEOFF FROM PIT, 'L MLG DOOR' MESSAGE APPEARED ON DISPLAY. CREW RECYCLED GEAR WITH SAME RESULT. FLT RETURNED TO PIT AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE LEFT MAIN GEAR UPSTOP DAMPER. GEAR SWING WAS NORMAL. (M)