1996 Camry - OBDII code P0420

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Old 22 Apr 2005, 01:30 pm   #1 (permalink)
hweems
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Default 1996 Camry - OBDII code P0420

Our 1996 Camry 4 cyl wagon has 165,000 miles and has not burned any
oil. We get a check engine light sometimes and each time the code
reads PO420 - "Catalyst System Efficiency Below Threshold-Bank 1".
Funny thing is that it does not come on in winter months. Also, it
only appears after driving some distance, say 50 -100 miles, then
stopping at a stop light, upon pulling away from the stoplight the
light comes ON.
After reading some postings, I interpret this code as a degradation of
the signal difference of the two oxygen sensors. In other words, there
is little difference in the signal before and after the catalytic
converter as measured by the oxygen sensors. Carbon monoxide coming out
of the engine should be converted in the nickel catalytic converter, so
the carbon monoxide reading should be lower in the post converter
oxygen sensor. This could mean a bad sensor or bad catalytic converter,
or possibly both.
The question is: How does one decide on which is responsible?
My thought is that if the catalytic converter is bad, then it would
read bad every time you start the engine, unless it is not totally bad
yet. Also, if a sensor is going bad it may not breakdown until some
driving, after which is is really hot for some time period. Then
again, if the sensor is totally shot it should real bad all the time
too.
Any thoughts appreciated on a line of attack.
I have 1 year before emissions retesting.
Thanks, HW

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