As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FAULT FOR ESCAPE SLIDE LT/ EPSU (12WL) EXT R SHOWS ON MCDU AFTER EMERGENCY POWER SUPPLT UNIT BITE TEST. MAINTENANCE REPLACED THE R3 DOOR SLIDE ASSEMBLY AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK OF THE EMERGENCY LIGHTING SYSTEM WITH NO FAULTS NOTED.