Train gradual stop departing BBT SB in AM. TC tried ATPM but max speed was 4kph. Tried shut down andopen up cab, fault cleared and train able to proceed normal ly in AM. ~~~~~ During powering found 2678 BC pressure at 0.25/0.22. Changeout ACU. ACU S/N: Old : 1532-115. New : 1549-217. Refer notif.2171531 Name                                 : Fauzi Date of occurrence                   : 18/06/2020 Last service date                    :   EMU/Equipment/Location               : 678/ACU/2678 Equipment Serial Nos.(if any)        : Old : 1532-115                                                 : New : 1549-217 Description of fault/Cause           : BCP pressure 0.27 Measurement (if any)                 : N.A Required rectification               : To Replace Checked during 3 weekly - OK. 29/6/20 (V-D).