What was found
DURING CRUISE THE CABIN DOOR OPEN CAS MESSAGE APPEARED FOLLOWED BY THE CHECK DOORS CAS MESSAGE. WE FOLLOWED THE QRH AND CALLED MAINTENANCE. WE AGREED TO DIVERT. UPON SHUTDOWN, WE DELAYED OPENING THE DOOR AND FEEL LIKE WE COULD ONLY RELIABLY SEE ONE DOOR PIN FLAG SHOWING LATCHED. CORRECTIVE ACTION: COMPLIED WITH REMOVAL OF FWD PROXIMITY SENSOR (S1) DUE TO SUSPECTED FAULTY SENSOR AND INSTALLATION OF A NEW FWD PROXIMITY SENSOR (S1) PERFORMED OPS CHECKS, OPS CHECKS ARE GOOD. IAW CE 680A AMM 52-70-10. NO DEFECTS NOTED. P/N ON / OFF: S2800-1257. NSN.