DTC P0420: Catalyst System Efficiency Below Threshold: Condition

DTC is set when value from Heated Oxygen Sensor (HO2S) No. 2 becomes closer to value from HO2S No. 1. MIL is illuminated when Engine Control Module (ECM) detects malfunction during 2 consecutive drive cycles. Possible causes are:

• Exhaust system malfunction.
• Catalytic converter malfunction.
• HO2S No. 2 malfunction.