As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: CABIN EMERGENCY LIGHTS NOT OPERATING USING THE CABIN EMER LIGHTSWITCH ON THE FA PANEL NOR WHEN USING THE COCKPIT EMER EXIT LT SWITCH UNLESS AN AC SOURCE IS AVAILABLE. PERFORMED BITE OF THE PTP AND FOUND FAULT MESSAGES "EPSU UNIT FWD L" AND "EPSU COMM AFT L".TEST OF THE FWD L EPSU SHOWED UNIT FAULT. MAINTENANCE REPLACED FWD EPSU UNIT IAW AMM 33-51-38.