As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT 1594 - AFTER LEVEL OFF AT FL 250, CREW RECEIVED THE LEFT OIL FILTER BYPASS INDICATION. LIGHT REMAINED ON WHEN THRUST WAS REDUCED. CREW SHUT DOWN LEFT ENGINE. FLIGHT RETURNED TO PIT AND LANDED WITH NO FURTHER INCIDENT. MAINTENANCE CHECKED THE OIL FILTERS AND FOUND NO CLOGGING MATERIAL. FOUND THE LEFT ENGINE OIL FILTER BYPASS SWITCH BAD AND REPLACED IT. (M)