ATSS alarm showed CBTC applied EB due totrain doors opened while moving. A side cab door opened by itself. TC closed cab door, reset EB and proceeded to next s tation in Auto mode with no abnormalities ~~~~~ ATSS alarm showed CBTC applied EB due to     Check #3501 cab door A/S found door intermittenty DIR & DMI extinguished even though door not positivety latched.Adjusted DSS rigging,DIR & DMI able to accurately reflect if door was open or closed.Additional checks,DSS contact resistor satis.No sign of FOD found.ER downloaded on PTU006,no abnormalities found apart from reported fault.Door cyclic test,satis.Door able to positively latch,security check ok. Done by Benjamin. 09/12/21