DTC P0420: Catalyst System Efficiency Below Threshold: Condition

DTC is set when value from HO2S No. 2 becomes closer to value from HO2S No. 1. This circuit is monitored once per drive cycle. MIL is illuminated when Powertrain Control Module (PCM) detects malfunction during 2 consecutive drive cycles. Possible causes are:

• Exhaust system leak.
• Catalytic converter malfunction.
• Fuel system malfunction.
• HO2S No. 1 malfunction.
• HO2S No. 2 malfunction.