Does anyone know the Denso part number for P0420 - Catalyst System Efficiency below Threshold Bank 1 . I changed one 02 Sensor a few months back with a Denso but I guess I need to change another one. A picture of the location would be great! I have a 2009. The Last one I changed was on the bottom but the plug was tricky to connect, as you had to reach behind blindlyup top near the firewall to connect it. I left the old wires in place as there was no room to reach in and unclip them. I just cut the sensor off. The vehicle has 220,000 runs fine gets good gas milage, I just getting tired of reseting the check engine light every fill up.