As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ON DEPARTURE, AUTOPILOT B WOULD NOT STAY ENGAGED. TRIED AUTOPILOT A AND IT WAS TOTALLY LOCKED OUT, B WOULD ENGAGE FOR ONLY A SECOND OR TWO. ACFT DID AN AIR TURNBACK FOR MAINTENANCE. FAULT WAS ISOLATED TO THE A SYSTEM ELEVATOR PRESSURE SWITCH. UNIT WAS REPLACED IAW 22-11-40-400-801.