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Thread: P0420 on my Sunfire.

  1. #1 P0420 on my Sunfire. 
    Car Enthusiast CF Newbie
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    2000
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    Pontiac
    Model
    Sunfire
    My check engine light came on, I checked it and it is reading a DTC P0420. I'm thinking the code either means my pre-converter O2 sensor is gone or the converter is gone. But I am not finding any power loss while I'm driving or any excess exhaust. The check engine light came on after I filled up my car with gas, I wasn't sure if the gas condition would effect the converter's ability to clean up the exhaust. I was wondering if anyone could narrow the problem for me. I have purchased an O2 sensor but don't want to put it in yet until I know that could be the problem. Thank you for the advice.
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  2. #2  
    Car Enthusiast CF Member JypsiDRIVER's Avatar
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    Achieva
    Autozone does free code readings and will tell you exactly what the issue is.
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  3. #3  
    Car Fanatic CF Senior Member
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    It most likely is the converter but there's always a chance its the downstream 02 sensor or that you have an exhaust leak. You can switch the 2 sensors around and see what happens and check for exhaust leaks, other than that your looking at a new converter.
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  4. #4  
    Car Enthusiast CF Newbie
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    Sunfire
    Thanks for the info. I have a code reader myself and it just says the threshold is below the limit and it says bank 1. Thats why I was thinking it may be the upstream O2 sensor, but I have read that it could be an exhaust leak as well. To help me narrow down where a leak could be, where would the leak have to be to cause such a DTC or does it matter? I can try switching them, I thought the O2 sensors were different? So they are interchangable? I hope its the O2 sensor, the converter will cost a good bit more. If so I'll have to start a thred about replacing the converter lol.
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