DTC P0420: Catalyst System Efficiency Below Threshold: Condition

DTC is set when value from HO2S-2 becomes closer to value from HO2S-1. MIL is illuminated when ECM detects malfunction during 2 consecutive drive cycles. Possible causes are:

• Catalytic converter malfunction.
• Exhaust system malfunction.
• Fuel system malfunction.
• HO2S-1 malfunction.
• HO2S-2 malfunction.