What was found
CAPTAIN REPORTED THAT BEFORE TAXYING, THE LE FLAPS TRANSIT LIGHT TURNED ON; MAINTENANCE PERSONNEL PERFORMED CHECK AND LIGHT LE FLAP TRANSIT WAS DEFERRED IAW MEL 27-04-02B; AIRCRAFT REJECTED TAKEOFF AT 20 KNOTS, DUE TO LE FLAPS EXT LIGHT TURN ON; MAINTENANCE PERSONNEL PERFORMED BITE TO FSEU IAW FIM 27-51 TASK 801 PROCEDURE, SHOWING FAILURE CODE 27-81222 F4 PROX RETRACT; SO LE FLAP 4 RETRACT SENSOR WAS REPLACED IAW AMM 27-88-11-000/400-802, TEST CORRECT.