Train came to a gradual stop after departing MRB2 with TIMS showing BCU fault at the front M1 car (n o. 1688). Fault cleared after TC switched to ATPM mode. Trai n continued to MSP2 in Auto mode thereafter. ~~~~~ Checked and confirmed #3688 ACU faulty. Heavy air leaking from solenoid course exhaust. Replaced ACU and carried out brakes/cyclic function test-ok. ACU-Old s/n: 1547-087  New s/n: 1525-054. Not: 2145328 raised to RSW. Done by Sateesh/Koh. 27/03/20.