As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TUS CREW REPORTED AUXILIARY POWER UNIT FAULTED WITH RT GEN ON PLACARD. EMER DECLARED FLIGHT RETURNED TUS LANDED WITHOUT INCIDENT. ACFT REMOVED FROM SERVICE. REPLACED APU FUEL CONTROL & ELEC CONTROL UNIT REPLACED. SYS GND CHECKED NORMAL, OPERATION CLOSED.