What was found
AIRCRAFT RETURNED TO GATE DUE TO A LE FLAP TRANSIT LIGHT ILLUMINATED AND LE DEVICE SLAT 1 LIGHT DID NOT ILLUMINATE. PERFORMED A BITE OF THE FSEU IAW FIM 27-51 TASK 801 PROCEDURES, SHOWING FAILURE CODES 27-81216F1 PROXIMITY RETRACT FIM 27-88 TASK 805 PROCEDURE WAS PERFORMED, DETECTING PROXIMITY SENSOR S1 168 WITH FAILURE. THE SENSOR S1 168 WAS INTERCHANGED WITH AFT ENTRY DOOR SENSOR IAW AMM 27-88-11. THE AFT ENTRY DOOR SENSOR WAS REPLACED IAW AMM 52-71-11-000-801 AND -400-801, TESTED CORRECT.