As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: MAINTENANCE REPORTS DURING PS CHECK, EMERG LT/EPSU (13WL) AFT L FAILED OPS TEST. REPLACED BATTERY 13WL IAW AMM 33-51-38, NO HELP. REPLACED EPSU 13WL STILL NO HELP IAW AMM 33-51-38. DETERMINED THE CAUSE TO THE L4 SLIDE. REMOVED AND REPLACED THE L4 SLIDE IAW CARD 26L00025010. OPS CHECK GOOD.