What was found
PART 91 FLIGHT, NO PAX ONBOARD. FLIGHT LEVEL 27,000 PILOT RECEIVED A FADEC NO DISPATCH, AND THEN SUBSEQUENTLY FADEC FAIL. HAD RED X’S ON MULTIPLE ENGINE DATA READOUTS, BUT NO ENGINE PERFORMANCE CHANGE. PILOT WAS ENROUTE TO ADDISON, HE FOLLOWED ONBOARD CHECKLISTS TO RESET THE SYSTEM, DIVERTED TO AMARILLO, DECLARED AN EMERGENCY IN THAT DIVERSION AS THE WARNINGS HAD NOT CLEARED. AS SOON AS HE GOT INTO CLEAR AND WARMER AIR ALL WARNINGS WENT AWAY (ABOUT 10 MILES FROM THE FIELD) WE CALLED CIRRUS/WILLIAMS AOG. THE TECH IMMEDIATELY STATED THE FADEC FROZE IN THE ICY COLDER CLOUDS. HE EXPLAINED THIS IS A VERY COMMON OCCURRENCE AND SINCE THE WARNINGS ALL WENT AWAY IN FLIGHT, AND THE WARNINGS ARE STILL CLEAR. THEY CLEARED THE AIRCRAFT FOR RETURN TO SERVICE. ENGINE AND SYSTEMS ARE PERFORMING NORMALLY.