What was found
FLT 907, JFK-ORD, SLAT LO RATE MESSAGE ON EICAS, FIRST APPEARED AFTER TAKEOFF ON FLAP RETRACTION. SLAT FAIL MESSAGE DURING FLAP EXTENSION. SLAT FAILED BETWEEN LEVER POSITION TO 0 AND 1. PERFORMED SYSTEM TEST IAW FIM TASK 27-53-00-810-803A & IAW FIM TASK 27-53-00-804A, SYSTEM OPS CHECKS GOOD, NO DEFECTS NOTED. TSI N236TO1018 TROUBLESHOOTING OF SLAT FAIL ASSIGNED. COMPLIED WITH TSI 236TO1018, REMOVED & REPLACED SLAT SKEW SENSOR LEFT REF AMM 27-83-01, OPS CHECK GOOD AT THIS TIME.