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high nitrogen oxide reading in emissions test - 1.7 gpm and limit is 1.5gpm Forums > > high nitrogen oxide reading in emissions test - 1.7 gpm and limit is 1.5gpm high nitrogen oxide reading in emissions test - 1.7 gpm and limit is 1.5gpm
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Old 09-25-2022, 02:12 PM
jjdonohue jjdonohue is offline
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2002 Pathfinder
Join Date: Jun 2020
Posts: 2
Question high nitrogen oxide reading in emissions test - 1.7 gpm and limit is 1.5gpm

i did emissions the other day and my 2002 pathfinder passed hc and co, co2 emissions but not nitrogen oxide apparantly, the state of california's standards have infiltrated colorado where i live as of jan 1st 2021. anyway, i passedbefore and now i dont. being an old car, im a little worried that i might not be able to bring it into compliance. However, some background - about 2 years ago i had a P0420 code which is the right bank (passenger side) catalytic efficiency below 95% or someting. so i assumed this would be a cat or o2 sensor issue. i replaced these myself. it worked fine after that, no check enginer light after i did that.
fast forward to now and the emission inspection for Nox fails only. i pulled obd scanner info at my local oreillys and what do you know, no codes and no emissions issues per the scanner. so now the state is telling me i have a failing vehcile but as far as the pathfinder specs are concerned, it is ok. i know a higher nox reading indicates a lean fuel mixture. i dont know exactly where i shuold be at but i took some fuel trim screen shots on the scanner. at 2175 rpm, the scanner says o2 b1s1 is 8.6% and same for stft b1s1. for 02 b1s2 it says 9.4% and stft b1s2 is 9.4% too. when idling at 763 rpm, the numbers are stft b1 = 12.5, ltft b1 =9.4, stft b2 =11.7% and ltft b2 = 9.4%. not sure what this all indicates but if anyone knows that would help. Or if i need other readings, please let me know so i can obtain them.

i started researching this and i came to realize the high nox could be caused by alot of things. i know the driver side cat and 02 sensors are the original but passenger side is only 2 years old as i mentioned. i have about 165k miles on this car. so i know thats one possibility but again no codes. i wonder if it could be a clogged egr, failed pcv valve ( super hard to get to) or a vacuum leak somewhere or maybe an exhaust leak someplace that i dont know about. again, no codes from the computer. thoughts on this? i would like to try and avoid a costly repair because the state has limits that are unreasonable for an old car. i also thought about running cleaners through the car like heet to see if i could "fake it" and pass.
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