CEL is back on and giving me the same P0420 code after I fixed a small exhaust leak between the front O2 Sensor and the CC. The CEL stayed off for about a week or so and came back on after a 60 mile drive the other day. I checked the FSM and found the ohms test for the O2 sensors. The front sensor spec. is 5 to 7ohms and the sensor was reading 8.9ohms (outside limitations). Anyone know how reliable that test is?????????? Also tested the rear O2 Sensor and it was well within the required spec. Recommendations????