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Home >> Subaru >> 2021 >> Forester Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System (Diagnostics) (2 Of 4) >> Diagnostic Procedure With Diagnostic Trouble Code (DTC) >> DTC P0420: Catalyst System Efficiency Below Threshold Bank 1 >> General Description >> Outline Of Diagnosis

Outline Of Diagnosis

To confirm the performance of Three-way Catalytic Converter (TWC), measure Oxygen Storage Capacity (OSC) using A/F sensor and rear oxygen sensor.