As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FOUND PROBLEM TO BE IN THE "FORCE TRIM CB ON" LOGIC. PREFLIGHT TEST IS NORMAL HOWEVER AUTOPILOT WILL NOT ENGAGE. ENTERED DIAGNOSTIC MODE AND INTO THE DISCRETE I/O SCREEN. FOUND BIT NR 13 OF PORT 1 IN THE DISCRETE INPUTS TO BE "1" WITH THE FORCE TRIM CB IN. CYLCED THE CB REPEATEDLY AND THE INPUT RESPONSE WAS INTERMITTENT. CHECKED FOR PROPER VOLTAGE AND GENERAL CONDITION OF PIN 56 IN RACK CONNECTOR 9A1P2 AND CHECKED OK.