What was found
(CAN) LEFT HAND BRAKE OVERHEAD WARNING MESSAGE DURING CLIMB OUT FROM DEPARTURE POINT. BTMS TEMP INDICATORS INITIALLY INDICATED MAX TEMP BUT THEN DISPLAY WENT BLANK. AN EMERGENCY WAS DECLARED AND CREW ELECTED RETURNED TO DEPARTURE POINT. ON LANDING AND BRAKE TEMPERATURE WAS NOT EXCESSIVELY HOT. AIRCRAFT WAS INSPECTED BY MAINTENANCE AND RELEASED UNDER MEL 32-46-01, HOWEVER, AFTER FLYING TO A MAINTENANCE BASE, THE NR 1 BRAKE TEMP MONITOR SENSOR WAS REPLACED.