Home >> BMW >> 2012 >> 335i 2D Convertible, Automatic Trans >> Repair and Diagnosis >> Engine Performance >> System >> Self Diagnosis - N55 - Diagnostic Trouble Codes - DTC P0478 (BMW DTC 138101) Through DTC P0440 (BMW DTC 191D01) >> DTC P0420; BMW DTC 180001: Catalytic converter: efficiency below limit value >> Fault code