EA190 RETURNS TO DEP ARPT FOLLOWING RECEIPT OF A PAX DOOR OPEN EICAS MSG.

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EVERYTHING WAS NORMAL DURING PREFLT; THE LOGBOOK WAS EXAMINED AND A DAILY CHK HAD BEEN DONE. ALL PREFLT PROCS AND CHKLISTS WERE DONE PER COMPANY POLICIES AND PROCS. WE HAD A FULL AIRPLANE AND BOTH THE FLT ATTENDANT AND COCKPIT JUMPSEATS WERE FULL. WE TAXIED OUT AND RECEIVED OUR WT AND BAL INFO AND DEPARTED. TKOF AND CLBOUT WERE NORMAL. PASSING THROUGH 10000 FT AND FL180 WAS UNEVENTFUL AND WE WERE HEADING OFF FOLLOWING OUR DEP ROUTING TO ZZZ1. THE WX WAS VFR WITH EXCELLENT VISIBILITY AND MINIMAL CLOUD COVER AND TURB. CLBING THROUGH FL290 WE HEARD A WARNING TONE AND NOTED AN EICAS MESSAGE. IT INDICATED THAT THE PAX ENTRY DOOR WAS OPEN. I WAS THE PLT MONITORING AND THE FO WAS FLYING. WE BOTH QUICKLY PULLED OUT OUR QRH'S AND REVIEWED THE PROCS. I ALSO REQUESTED TO STOP THE CLB TO OUR CRUISE ALT (I THINK I RECALL BEING ASSIGNED FL360). I NOTED THAT THE PRESSURIZATION WAS NORMAL; CABIN ALT WAS ROUGHLY 6000 FT WITH ROUGHLY 7 PSI DIFFERENTIAL. BASED ON MY PREVIOUS ACFT EXPERIENCE (MOST RECENTLY AIRBUS 320; ETC); I SUSPECTED AN INDICATION PROB ONLY. HOWEVER; AS THE FO AND I REVIEWED THE QRH IT GAVE LITTLE LATITUDE AS TO OUR COURSE OF ACTION. THE E190 QRH HAS THE PROC. THE SEATBELT SIGN WAS STILL ILLUMINATED IN OUR CLB. WE CALLED THE 'A' FLT ATTENDANT AND QUERIED HER ABOUT THE DOOR LOCK INDICATORS. SHE QUICKLY CHKED AND TOLD US THAT 2 OF THE GREEN DOOR LOCK INDICATORS WERE NOT FULLY SHOWING; HENCE; ONLY PARTIAL GREEN. ON THE GND IT HAD BEEN NORMAL SHOWING FULL GREEN. SINCE WE DID NOT HAVE A NORMAL INDICATION -- A MINIMUM OF 2 DOOR LOCK INDICATORS GREEN -- WE HAD TO FOLLOW THE QRH RECOMMENDATION: 1) LAND AT NEAREST SUITABLE ARPT (THIS CASE A RETURN TO ZZZ) AND; 2) ALT 10000 FT OR SAFE ALT. WE SPOKE WITH CTR ABOUT OUR NEED FOR LOWER; AND A RETURN TO ZZZ. THEY WERE VERY ACCOMMODATING AND HEADED US BACK TO ZZZ. WE GOT PROGRESSIVELY LOWER. AS WE WERE TURNING BACK; I ACARS'ED DISPATCH AND MAINT AND ADVISED THEM OF OUR RETURN TO FIELD. DISPATCH INDICATED HE WOULD ADVISE MAINT. PER THE QRH PROCS; AS WE PASSED 10000 FT; WE FOLLOWED THE PRESSURIZATION DUMP REQUIREMENT AND COMPLETED IT ABOUT 8000 FT. WE THEN CONTINUED OUR DSCNT AT ROUGHLY 500-1000 FPM TO REDUCE ANY EAR DISCOMFORT. WE ALSO GOT THE ZZZ ATIS INFO; LOADED THE LNDG INFO AND FOLLOWED ALL CHKLIST PROCS; INCLUDING DSCNT AND APCH AND OTHERS AS APPROPRIATE. THE FO CONTINUED TO FLY AND I WORKED THE RADIO AND RAN CHKLISTS/QRH PROCS. THE FO LANDED THE ACFT AND WE TAXIED INTO OUR ORIGINAL DEP GATE IN ZZZ. ONCE ON THE GND; MAINT MET THE ACFT AND EXAMINED THE 1R DOOR. THE DOOR HAD HAD A PREVIOUS WRITE-UP 13 DAYS PREVIOUSLY FOR EXACTLY THE SAME ISSUE. THE MECHS INDICATED TO ME THAT THE INDICATION (GREEN LOCK DISPLAYS) ISSUE WAS A RESULT OF A WORN CAM IN THE DOOR AND NOT BRINGING UP THE DOOR LOCK INDICATORS. IT DIDN'T EXPLAIN WHY THE INDICATION HAD CHANGED FROM THE INITIAL ARMING TO THE INFLT INDICATION. THE WORN CAM MAY ALSO HAVE CAUSED THE LOCK PROX SWITCH TO INDICATE AN UNLOCKED SITUATION. AFTER SOME ADJUSTMENT; WE LEFT AND THE DOOR WORKED NORMALLY.