As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI, CO-PILOT LEFT BRAKE PEDAL GOES TO THE FLOOR DURING BRAKE APPLICATION, PILOT BRAKES OPERATE NORMALLY. INSPECTED CO-PILOT'S MASTER CYLINDER, NO DEFECTS FOUND. APPLIED HYDRAULIC POWER AND CHECKED LEFT BRAKE PEDAL AND NOTICED IT WAS SPONGY. BLED BRAKE SYSTEM IAW CESSNA MM CHAPTER 32-42-00, SYSTEM OPS CHECKED GOOD.