As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - FLIGHT 2555 - AFTER ENGINE START RECEIVED A INTERM FIRE SYSTEM FAULT MESSAGE. RETURNED TO THE GATE, MAINTENANCE PLACED THE SYSTEM ON MEL 26-00-1. AIRCRAFT RETURNED TO SERVICE. TROUBLESHOOTING SHOWED A SHORT IN LOOP "A" ON THE LEFT SIDE MEL CONTINUED. REPLACED LOOP ELEMENT "A". OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.