As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ON STARTING SECOND ENGINE, THE PILOT NOTICED THAT THE BRAKE PUMP MOTOR NOISE SOUNDED DIFFERENT THAN NORMAL. WHEN ENGINE STARTED, PILOT RELEASED BRAKES TO TAXI AND RECEIVED A 'POWER BRAKE LOW PRESSURE LIGHT'. ENGINES SHUT DOWN. THE BRAKE PUMP MOTOR RAN CONTINUOUSLY, BUT DID NOT MAKE ANY PRESSURE. FURTHER INVESTIGATION SHOWED THAT THE COUPLING HAD FAILIED.