July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

DTC P0420: Catalyst System Low Efficiency: Condition

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

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