Rear DT car DIR illuminated. TC opened and closed to no avail. Staff (CBR) confirmed Rear DT car, A1door unable to isolate. DIRBS operated. ~~~~~ Downloaded ER on PTU006. Checked door lock s/w, J-rail and door guide rail ok. Checked door operation using door PTU ok. From CCTV footage, door unable to close due to F.O.D. Suspect F.O.D dislodged during door cyclic. Found door isolation device damaged due to improper operation. Replaced damaged door isolation device ok. Carried out door cyclic & function test ok. Done by Joshua 04/02/20.