Train doors at rear DT car were not proven closed. TC recycled train doors a few times but to no ava il. Rear DT car 'B3' doors remained open when all train door s were proven closed. Pax was disembarked to BNL EB platform ERS-10 ~~~~~ 3627 B3 Train doors were not proven closed. Level 3. TC recycled train doors a few times but to no avail. Rear DT-3627 B3 doors remained open when all train doors were proven closed. Pax was disembarked to BNL EB platform. L3 3627 FC 3x #3627 B3 door close operation time-out. TC cycled doors 2x to no avail. Checked/found door operator faulty & replaced. Function check - OK. Cleaned J-rail & guide rail. Used scope to check roller condition - OK. Door cyclic test, door gap 63.5mm, open/close door, no DIR lit, TIMS door static timing test - Passed. All doors proven closed.  Sarma/Alan/Lee PT/Sugu/Shafie 44952 #3627 B3 Door Operator S/N : OLD : 1503W020001S023 NEW : 1506W020011S010