TC reported Front M2 car BCU fault. Train reduction in speed. TC operated STBS and proceeded in ATPMto BGB SB to disembark. SM BGB isolated Front M2 car BIC. ~~~~~ 2558 TC reported BCU fault. Train reduction in speed. Level 3. TC operated STBS and proceeded in ATPM to BGB SB to disembark. SM BGB isolated Front M2-2558 car BIC. L3 2558 BCU Fault (bog.#1 & #2), release fault, control pressure fault & emergy BCP (BOG.#1 & #2) ER shows 2558 BCP slow to release. BCP applied lower than criteria. Postulate ACU faulty resulting in BCP slow to release & abnormal BCP application . Side find found CP transmitter clip broken. Replaced ACU & CP transmitter. Preventively c/out BCU. Alan/Kamarul 45193 BCU S/N:(1823185-OLD) ; (1827120-NEW) ACU S/N:(1037/005-OLD); (1310/134-NEW)