TC reported train tripped in Auto mode due to Rear M2, B2 door were opened.om NOV SB - ORC SB and reported- no abnormalities.) boarded T445 at rear M2 car 'B2' door monitored for 3 stat ~~~~~ 2615 TC reported train tripped in AM due to B2 door were opened. Rear T226 conducted ATPM line clear from NOV SB - ORC SB and reported - no abnormalities. SM(ORC) boarded T445 at 2615 monitored B2 door for 3 stations and reported no abnormalities. Platform CCTV playback at NEW SB found no abnormality. In train CCTV playback for 2615, B2 door found no abnormality. ATS alarm showed: Train door status lost while train is moving. T247, T230, T250 were held by/held for regulation, schedule adherence at MSP were affected. Nl3 2615 checked/found no FOD. Weather strip, guide rail & J-rail checked - OK. Checked ER & found DIR de-energised while departing station, causing EB. FC at CLE & DOV at #2615 B2 door. Fault trace showed door physical gap of 56mm. 2 separate situations found : 1) DLS was not energised prior to fault. But DIR was energised. 2) DOBS repeatedly energised with door motor current    repeatedly dipping. OPS 20 raised to c/o DLS & DCP for investigations on door current.  Lee JC 44707 To changeout  DCP at 2615 B2 door.  2615 DCP replaced. Simulated FOD, door motor current & DOBS - Satis. Replaced DLS assembly. Door cyclic test & door ststic timing test - Satis. DIR able to extinguish.  Lee JC 44708