TC reported brake fault at front M2 car. ~~~~~ Downloaded ER and fault trace on PTU002. From ER observed #2559 BCP unable to regulate stuck brake. Carried out brakes cyclic test, found #2559 EM BCP 2.69 bar, failed criteria (2.75 - 3.25 bar). Replaced ACU and carried out brakes cyclic/function test ok. Checked all BCP within criteria. #2559- ACU: Old s/n: 1012-016.  New s/n: 1240-099. Not: 2160352 raised to RSW. Done by Kumar/Jack/Sateesh/Koh. 14/05/20.