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Lexus RX300: I have an 02 rx300 with a cat code P0420. Problem…

I have an 02 rx300...
I have an 02 rx300 with a cat code P0420. Problem I have is that there seem to be 2 catalytic converters monitored by the o2 sensors. which cat would it most likely be?
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Answered in 31 minutes by:
11/9/2012
Lexus Mechanic: lexpert, Lexus Master tech replied 9 years ago
lexpert
lexpert, Lexus Master tech
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There is only one catalyst monitored. The one in the exhaust manifold is the precat and is not monitored.
The one that is bad is the one in the undercrriage that is built into the center exhaust pipe. This is about a $1,200 part. Also you need to get a fresh set of factory iridium spark plugs put in if this hasn't been done recently. The 2 leading causes of catalyst failure on these is worn plugs and/or customers driving these vehicles with chec engine lights on due to failed o2 sensors. You MAY get lucky and avoid a new converter cost by putting a new set of plugs in it and resetting the computer.
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Customer reply replied 9 years ago

there is an o2 sensor right out of the manifold before the first cat too though.

Lexus Mechanic: lexpert, Lexus Master tech replied 9 years ago
Actually its not. There are 3 sensors on this. One air fuel ratio sensor in each manifold and then an o2 sensor behind the rear/main cat.
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