What was found
AFTER LANDING, APU FAULT ILLUMINATED. FOLLOWED QRH PROCEDURE. SECOND ATTEMPT APU FAULT LIGHT RE-ILLUMINATED. GROUNDED - YES. FOUND FAULT 49-15004 STILL CURRENT. REMOVED AND REPLACED APU AIR INLET DOOR POSITION SWITCH REF B737-900 AMM 49-15-41. C/W EA 900ER-49EA-263458 FOUND OLD SWITCH OUT OF RIG. C/W GROUND OPS VERIFICATION AND RAN/ STARTED APU MULTIPLE TIMES. NO DEFECTS NOTED, OPS TEST GOOD. NO FAULT CODES FOUND.