As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT, COPILOTS LEFT BRAKE PRESSURE WAS INSUFFICIENT. THE CREW TAXIED THE ACFT BACK TO THE RAMP. REPLACED THE HYD ACOUSTIC FILTER AT 9GXA IAW ATR-72JIC 29-10-00 RAI 10080. THE SYS CHECKED GOOD. THE BRAKE LOW PRESSURE LINE WAS BLEED IAW JIC 32-42-00 BLD 10000. THE NORMAL BRAKE SYS CHECKED GOOD.