Over the past few months I have been getting a P0420 code on a 1999 Acura CL 2.3L. It happens maybe every 1000 miles. At first I simply reset the code then changed the speed and O2 sensors. Seems an inexpensive try and an easy DYI. I thought I fixed it because I have driven the car for 3000 miles before the problem started again.
Today I monitored the O2 sensor (only has one) and the values are a little concerning but I am not sure what exactly it means and what to look for next. The monitor read between 0.155 and 0.850V at around 2000rpm and rapidly fluctuating up and down between the values. I heard and read that the value should be more or less stable at 0.5V. I am afraid it might point to a bad catalytic converter but am open to other ideas to look at. Btw, I do not hear any rattling or “funny” noise coming from it while driving or banging on it. I also passed emission testing (reset the code a few days prior).