As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: WHILE ACCOMPLISHING THE EMERGENCY POWER SUPPLY UNIT SYSTEM BITE TEST FAULTS FOR EXTERNAL AND INTERNAL LOAD DISPLAYED FOR EMERGENCY POWER SUPPLY UNIT 13WL. MAINTENANCE REPLACED EMERGENCY POWER SUPPLY UNIT 13WL AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 33-51-00.