As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING CLIMB OUT WITH AUTOPILOT "A" OR "B" ENGAGED, ENCOUNTERED CONSTANT TRIMMING OF AIRCRAFT NOSE UP AND THEN NOSE DOWN ALMOST CONTINUOUSLY. MAINTENANCE ADVISED A RETURN. DURING RETURN OCCURED AGAIN IN LEVEL FLIGHT AND HELD AT 12000FT. THE MODE CONTROL PANEL WAS REPLACED.