As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - FLIGHT 2399 WHEN AIRFRAME MODE SELECTOR SWITCH USED AT FAST AND SLOW, DE-ICE PRESSURE CAUTION LIGHT ILLUMINATED. IT APPEARED ALWAYS TO HAPPEN UPON ILLUMINATION OF LEFT INTAKE AND RIGHT INBOARD TAIL. PSI WAS ALWAYS 19-20, COMPLIED WITH CHECKLIST. MAINTENANCE NR 5 DUAL DISTRIBUTOR VALVE. OPERATIONAL CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.