Train stopped with stuck brake indication at Rear M2 car 1504after departing BBT SB. STBS operated . Pax disembarked at BGB. Train stopped with stuck brake ind ication at Rear M2 car 1504after departing BBT SB. STBS op ~~~~~ 2504 Train stopped with stuck brake indication after departing BBT SB. STBS operated. Pax disembarked at BGB. (L3) L3 3503 found STBS operated & #2504 BIC isolated. FC 308 (BCU Fault), FC 330 (BCU BCP Fault Bogie 1), FC 331 (BCU BCP Fault Bogie 2). ER D/L & showed that #2504 BCP applied at time of fault. Found #2504 ACU faulty, resulting in BCP unable to release & giving stuck brake condition. Solenoid resistance - No abnormalities. Brake frame no aie leakage. Normalised #3053 STBS & #2504 BIC. Swapped ACU from #2504 to #1504 & replaced #1504 with new ACU. Brake shoes & wheel condition checked/found no abnormalities. Brake cyclic test, BCP within criteria. Brakes able to release @ COAST> Depot shunting - OK. ACU S/N : (after swapped)    #1504 : 1012/015 (new) #2504 : 1008/002 faulty : 1302/129  Shaun Lau 45426