What was found
AIRCRAFT WAS GROUNDED: AFTER A COUPLE CENTER TANK ECAMS ON CLIMB OUT ORD ENTERED UNDERSEPARATE EMICS, GOT FUEL ECAM THAT ASKED IF FUEL LEAK SUSPECTED.ONLY A COUPLE HUNDRED LBS DIFFERENCE AT THAT POINT, ANSWERED NO AND CONTINUED CLIMB OUT. SEVERAL MINUTES LATER ECAM RETURNED AND CHECKED FUEL, LEFT INBOARD TANK WAS 1000 LBS LESS THAN THE RTTK AND DECREASING RAPIDLY. ANSWERED ECAM YES AND FOLLOWED ECAM TO SHUT DOWN LEFT ENGINE. EMERGENCY DECLARED RETURNED TO ORD, LANDED WITH 1900 LBS LESS IN LEFT TAKE THAN RIGHT. MAINTENANCE REMOVED AND REPLACED LEFT MAIN TANK UNIT #10 PROBE IAW AMM 28-42-15