P0420 code

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thundercat

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Hi I have a Pontiac Montana 2003, some times appear the P0420 code then I clear it. Around 3 years ago changed both O2 sensors to new ones, so I doubt failed some again.
I not noticed difference in the yield (apart the fact that this model was never characterized to have great acceleration), neither other codes. I hope not the catalytic converter. Does someone some idea to why is this P0420? Thanks
 
I loved this!:

"Run 1 gallon of lacquer thinner through the gas tank.. "
 
my thoughts ran more along stop guessing and use a scan tool to actually see what the O2 sensors are saying
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At weekend I will do a sequence of tests, first measuring temperatures in both ends of the CAT with the IR. Results will write then here..

( maybe could be a valid method, according to the link, drop a gallon of lacquer thinner at tank. But was really funny when I read this! )
 
Samples are in Celsius degrees

- Before turn on engine: Input 24.9, Output 25.2
- 34 minutes later turn on: Input 166, Output 172

Not enough hot at output end, then the CAT almost passed away. No money for buy a new one. Did somebody have experience with the Cataclean or similar product? Thanks
 
you cannt find a used one a junk yard?
 
Very probable (~ 50%) that is also bad or in their ends. Mine has good external appearance, however it doesn't reflect their internal condition
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Around a month ago changed bad IAC, and since then no codes

What was happening:
- Wrong air mix => outrange residual O2 at out
- Wrong residual O2 => wrong work of CAT (not measured temps again)
- Wrong residual O2 => detected at first O2 sensor as a anomaly
 
Didn't you had other related trouble codes together with the P0420 code? Normally if you have a lean mixture, the first O2 sensor should put out a lean mixture trouble code. The engine control unit is just calculating the temperature of the catalytic converter based on a lot of parameters. Leaner or richer mixture can cause miscalculations of the temperature which can cause the code to appear. Other stored trouble codes can also make the engine control unit to not calculate the temperature at all, but as said if this is the case, there should be other stored trouble codes.
It's not common but over time it can cause the catalytic converter to not work properly.
 
thanks for the update
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