As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: ON CLIMB OUT PASSING 5000FT AND MAINTAINING 250KTS ENGAGED AUTOPILOT-B. A BUMP WAS FELT AND AIRCRAFT WAS THEN UNABLE TO MAINTAIN PITCH AND AIRSPEED. AUTOPILOT WAS DISCONNECTED AND AIRCRAFT WAS HAND FLOWN. THEN AUTOPILOT-B WAS REENGAGED WITH THE SAME RESULT. STAB OUT OF TRIM LIGHT ILLUMINATED. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT ORD. (OPEN).