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P0420 Nissan altima help?

Hi i have a 2003 Nissan altima 80,000 miles on it, i recently got the code p0420 and when i checke the code it said catalytic something under threshold, thing is i went to the emissions test and passed with the code on there my cat was fine,o2 sensors fine and no exaughst leaks ? was wondering if anyone knew what possibly was going on ? could it be my computer in the car ? putting out a code that isnt actually an issue ?

ps.. i just bought this car 1 month ago i am the 3rd owner and the car has been in an accident before so what im thinking is the computer in the car was messed up during the accident.
in resp to the answer i just got… i had the light on and the code during the smog test, it was active as i got it tested so the light was a problem during the test but my car still passed the expection

    Posted 2 years ago

    It may not have been an issue when you had the car smogged, but it’s an issue now. (Similarly, flat tires previously had air in them.)

    You should probably hope that the computer isn’t messed up, because it would likely cost you more than the cat you’re about to buy.

      Michael Larson
      Posted 2 years ago

      bad o2 censor , bad catalytic converter , Bad ECM program.
      the ECM is most probable cause because there has been problems in the past with these cars. Reprogram the ECM will increase the range of the O2 sensor signal, and alot of the time the software is out of date and a new one is downloaded from the dealer. I recommend reprogramming the ECM first, before replacing any other parts.the

        MasTec 1970
        Posted 2 years ago

        Your catalytic converter has degraded (You did not mention in what state you live) You can still pass emissions with a degraded converter, because the state in which you live does not do an OBDII monitor check on your vehicle or you would have Failed (the State where you live only does a tailpipe test) You also did not mention the engine option in your Altima is it a 2.5L 4 cylinder or the 3.5L V-6? If is the 2.5L the is a recall covering this concern and a possible fire hazard! This is a VOLUNTARY RECALL CAMPAIGN ALTIMA AND SENTRA QR25DE ENGINE EXHAUST PIPE HANGER PIN AND PRE-CATALYST! If your vehicle fits the application criteria you will get a new pre-Catalytic converter (this is the one that is monitored by the PCM) and Exhaust Pipe Hanger Pin kit, New heat shields. and the PCM will be flashed (reprogrammed) to prevent future damage to the pre-cat.

        Here: http://www.justanswer.com/uploads/ebrock63/2009-03-02_180958_recall.pdf

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