Train undershoot 2.5 metres in AM. ECB was subsequently activated at rear M2 car. ECCBS was operatedfor train to proceed in ATPM to CSP. Staff(SOM) assisted an d reset ECB for train to depart. ~~~~~ [Level 3] [NSEWL] T203(3532) ECB Activated - SOM NB: Train undershoot 2.5 metres in AM. ECB was subsequently activated at rear M2 car. ECCBS was operated for train to proceed in ATPM to CSP. No incident. Staff(SOM) assisted and reset ECB for train to depart. LTOC was informed L3 Check FC 3532 308, 312,314, Unable to duplicate fault. Replace ACU, Function test ok, Brake within criteria. Security check ok. new:1020-001 old:1025-009 notif:2522758 Done by Rizman/Roslie 45180