DTC P0420: Left Bank Catalyst System Low Efficiency: Condition

DTC is set when value from HO2S bank No. 1 (left bank) sensor No. 2 (B1 S2) becomes closer to value from HO2S bank No. 1 (left bank) sensor No. 1 (B1 S1). MIL is illuminated when Power Control Module (PCM) detects malfunction during 2 consecutive drive cycles. Possible causes are:

• Exhaust system leak.
• Catalytic converter malfunction.
• HO2S B1 S2 malfunction.
• PCM malfunction.