As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: DURING EMERGENCY POWER SUPPLY SYSTEM TEST, EMERGENCY POWER SUPPLY UNIT 17WL DISPLAYED FAULT MESSAGE ON THE CIDS. MAINTENANCE REPLACED EMERGENCY POWER SUPPLY UNIT 17WL AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 33-51-38.