# code P0420



## uglycars (Sep 23, 2017)

Hey guys,
new here so i will try to get this right. I have a 2006 nissan altima 2.5L with 238500 miles. it has recently had the check engine light come on. when i checked it, the code came up P0420. i dont have any others showing. this one comes and goes, but it is always the same code. when the check engine light is on, i can sometimes smell exhaust and sometimes fuel fumes sitting at red lights. I am looking into replacing the the exhaust manifold/catalytic converter with my next paycheck. i know it could be some other stuff. i am a backyard very amateur handy man. i can swap stuff out but i dont know how to check most of it. i figured that would be a good first move. i just need some other opinions or stuff to check. thanks in advance for all the help guys.


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## theskater101388 (Mar 4, 2010)

P0420 is just the rear O2 sensor saying your rear/downstream cat is going bad. Lot of times it is just a bad sensor and swapping it out for a new one (buy online for half the price of local stores) will normally solve the problem. If it doesn’t, then it’s your downstream cat, but I’m buying it’s just the sensor and the common thing to do first is replace sensor as it is the cheaper part. This code won’t affect performance or anything btw so don’t worry about having to rush to solve the issue either


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