Home >> Subaru >> 2017 >> Forester 2.0XT Touring >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Control System (Diagnostics) (P0171 To P0685) (H4DOTC) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0420 Catalyst System Efficiency Below Threshold Bank 1 >> Component Description