What was found
CABIN DOOR OPEN CAS ILLUMINATED WHEN PREPARING FOR FLT. CYCLED DOOR IAW QRC. LIGHT REMAINED. PERFORMED OPS CHKS & CLOSED MED. TURNED OFF BLEED AIR & FOUND CAS MESSAGE. WENT INTO CMC & FOUND LOWER LOCK VENT DOOR SHOWING OPEN. FOUND DOOR BRUSH SEAL DAMAGED & MISSING A FASTENER. FOUND VENT DOOR PROX SENSOR TARGET MISSING, PERFORMED OPS CHECK & PUSHED VENT DOOR CLOSER & VERIFIED CAS EXTINGUISHED & RETURNED WHEN LET GO, LOOKED INTO MED & FOUND TARGET LODGED UNDER FOAM TAPE. CLEANED & REAPPLIED TARGET. PERFORMED OPS CHECK WITH DOOR STEPS & ACCESS PANELS REMOVED, NO DISCREPANCIES. INSTALLED NEW BRUSH SEAL. PERFORMED OPS CHECKS, DOOR CLOSED, NO DISCREPANCIES. WORKED IAW SPM 20-00-00, 20-40-30 & AMM 52-70-00.