Train Prep staff reported #2555 having B ~~~~~ ER downloaded. FC312 - BCU release fault Fault able to duplicate in depot Checked and found 2555 brake unable to release from EM to Coast Fault transferred when ACU swapped from 2555 to 1555 Replaced faulty ACU. Function test and depot shunt - ok FC 312-BCU RELEASE FAULT ACU (1555) NEW-1047/084 OLD-1042/073 N.A //15.02.23