Hey, so my 2000 Hyundai Accent Hatchback (manual) is tripping the code P0422 (Main Catalyst Efficiency Below Threshold (Bank 1)). If i clear the code it will pop back up after about 40-60 miles of driving. I hooked my OBDII sensor to it and look at the voltage output from the two O2 sensors and the front one oscillates between .2 to .7V and the downstream one does as well switching about at the rate. From my understanding the downstream O2 sensor should stay fairly steady or at least switch much slower than the upstream one. I get pretty good gas mileage, typ. ~30mpg. Luckily my state does not have emission testing. Any idea if it is actually the catalytic converter, the downstream O2 sensor or something else? Any help would be appreciated. Thanks!