What was found
AFTER TAKEOFF FROM DCA, THE CREW RECEIVED A LG AIR/GND FAIL MESSAGE ON THE EICAS. THE CREW ATTEMPTED TO RETRACT THE LANDING GEAR AND THE GEAR SELECTOR WOULD NOT MOVE. SAFE CLIMB WAS NOT AFFECTED BY TERRAIN SO AN OVERRIDE WAS NOT ATTEMPTED. THE CREW FOLLOWED THE PROCEDURES IN THE QRH AND DIVERTED TO IAD. THE CREW DECLARED AN EMERGENCY AND REQUESTED CFR TO BE WAITING. THE FLIGHT THEN LANDED WITHOUT INCIDENT AND TAXIED TO THE GATE. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND 3 MLG PROXIMITY SWITCHES TO BE FAILED. THEY REMOVED AND REPLACED THE SWITCHES IAW AMM 32-61-02. ALL OPERATIONAL CHECKS WERE SATISFACTORY.