2005, check engine light tripped code P0420, research points to bad catalytic converter or o2 sensor...50/50 city/hwy MPG is 53 per tank. Thing is, I just replaced the catalytic converter and o2 sensor 2000 miles ago. Posted images from torque pro on the voltage readings for the upstream A/F sensor and o2 sensor...noticed while driving with ICE running at 55mph the O2 sensor voltage will occasionally bounce from 0.7 down to 0.1, so maybe bad electrical connection tripping the code? Also, isn't 4.0 volts for the upstream A/F sensor above nominal, as in a lean condition? A/F ratio cruising at 55 mph is around 14.65-14.7.