As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MECHANIC NOTICED POWER BRAKE PUMP STOPPED CYCLING AFTER FLIGHT, IT NORMALLY CYCLES EVERY MINUTE OR SO TO RECHARGE PRESSURE ACCUMULATOR. LACK OF CYCLING TRACED TO OPEN PRESSURE SWITCH WHICH WAS REPLACED AND OPS RETURNED TO NORMAL. SUBMITTER HAS HAD TO CHANGE THESE SWITCHES 15 TIMES OVER THE LAST 7 YEARS ON FLEET OF FOUR C-550'S.