I have a 2002 Sienna with the same problems after I replaced Bank 1, Sensor 1. Check engine light disappeared for a little while and then came back with the P0420 code and saw your posting.
Could you clarify the sensors you replaced. I got a little turned around in your explanation. I highlighted the sensors in question. It may seem you typed something other than what you were thinking? Thanks.
-Mao
Quote:
Originally Posted by pjksr02
A week later I got code P0420. Using my OBD reader, I found my Bank 1, sensor 2 voltage jumping up and down, rapidly, seeming to indicate a bad catalytic converter. My Bank 2, sensor 1, and bank 2, sensor 1 resistances were good.
For fun, I replaced bank 2, sensor 1, since it is so easy to do. Immediately after starting my engine, a light plume of white smoke came from the tailpipe for about 20 seconds. That'd never happened before.
My Bank 1, sensor 2 voltages now no longer oscillated as fast or as much, indicating better catalytic converter function. I cleared my P0420 code, and it has not reappeared in several hundred miles of driving, and my readiness monitors are "ready."
So, if you get a P0420 on a Sienna, I'd recommend replacing both A/F sensors. You can get Denso models for about $140 if you look, online.
~Pete
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