The service light came on and the code is PO420 for Catalyst efficiency. that code is for the down steam O2 passed the catalytic converter. The front oxygen sensor should switch frequently (constantly yo-yoing between about 0.1 and 0.9 volts).
How to diagnose, repair, and info on symptoms and causes of a P0420 OBD-II So this engine code article applies to Nissan, Toyota, Chevrolet, Ford, Honda.
P0420 FORD | Catalyst System Efficiency Below Threshold Bank 1 | The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen.
Repair Information for P0420 Ford code. Learn what does P0420 Ford Catalyst System Efficiency Below Threshold Bank 1 means, location and how to repair?.