What was found
RETURNED TO GATE, WHEN AUTO FEATHER WAS INITIALLY SELECTED, ALL INDICATIONS WERE NORMAL. 24 HOUR SYSTEM TEST WAS NORMAL PRIOR TO TAXI AS WELL. DURING TAXI, AFTER CHECKLIST WAS DONE, INDICATIONS FOR AUTO FEATHER ON BOTH SWITCH LIGHT AND ED DISAPPEARED, THERE MAY HAVE BEEN A POP ASSOCIATED WITH INDICATING FAILURE. FOUND CDS FAULT CODES 64, 494. FOUND AUTO FEATHER SELECT SWITCH WOULD NOT STAY ENGAGED IF SELECTED ON POSITION. REPLACED AUTO FEATHER SELECT SWITCH. OPERATIONAL TEST GOOD WITH NO RECURRENCE OF FAULT CODES OR DEFECTS NOTED. AIRCRAFT RETURNED TO SERVICE.