Hi all. My 2002 Ram 1500 with 360/auto has a code P0420 at left bank. Does this mean that small cat convt looking thing at the drivers side head pipe is bad, or is it possibly the 02 sensor? No 02 codes showing but looking for some advice prior to spending money on wrong parts. Btw the truck has all the original 02 sensors/cats and has 286,000 miles so I guess I got my monies worth! Thanks for any and all replies.