As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: MACH TRIM LIGHT ILLUMINATED DURING CLIMB. AIRCRAFT EXCEEDED ALTITUDE WHEN LEVELING. TURNED OFF AUTOPILOT AND HAD A LARGE NOSE DOWN TRIM RECOVERY. FLIGHT DECLARED AN EMERGENCY AND RETURNED TO ORD LANDING SAFELY. ACCOMPLISHED FIM 22-13-00. FOUND INTEGRATED FLIGHT SYSTEMS ACCESSORY UNIT (IFSAU) FAULTY. REPLACED IFSAU PER AMM 22-11-37.