As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED AN UNCOMMANDED TRIM NOSE DOWN WHEN ENGAGING AUTOPILOT. PROBLEM REOCCURRED REGARDLESS OF FLIGHT DIRECTOR COMMAND. RECREATED PROBLEM IN HANGAR. VERIFIED ALL TRIM SWITCHES OPERATIONAL WITH NO INPUT PROBLEMS. FOUND AUTOPILOT PITCH TRIM SERVO SENDING TRIM DOWN SIGNAL REGARDLESS OF FEEDBACK. REPLACED TRIM SERVO AND OPS CHECK GOOD.