*Originally posted in General Chat section, re-posted here for direct help*
Hey guys. I just sold my Yukon, and the new owner is saying that it just failed emissions today. By law, I am required to fix it or buy the truck back...which sucks. Colorado just started testing for Nitrous Oxide (NOX) emissions this year. The maximum allowable NOX reading is 2.0, and it's showing 2.27, just barely a failure.
The truck has NEVER failed a test before now. The exhaust is entirely stock.
It has a 91 octane tune, and I'm at altitude in Denver. Could the timing changes or whatever was done for the tune have something to do with the increased NOX readings? The new owner put 85 octane in it against my advice, and the CEL came on due to the knock sensors getting angry. He has since put 91 octane in it and had the code cleared by a mechanic friend of mine; it hasn't come back on to my knowledge.
It has a AEM Brute Force intake, new MAF sensor as of last year, new spark plugs/wires last year. All regular maintenance. Again, the exhaust is bone stock.
Any help is GREATLY appreciated. Gotta get this figured out quick, and I'd like to avoid shelling out $800 bucks for new cats if it turns out that replacing them is the only thing that will fix this.
Hey guys. I just sold my Yukon, and the new owner is saying that it just failed emissions today. By law, I am required to fix it or buy the truck back...which sucks. Colorado just started testing for Nitrous Oxide (NOX) emissions this year. The maximum allowable NOX reading is 2.0, and it's showing 2.27, just barely a failure.
The truck has NEVER failed a test before now. The exhaust is entirely stock.
It has a 91 octane tune, and I'm at altitude in Denver. Could the timing changes or whatever was done for the tune have something to do with the increased NOX readings? The new owner put 85 octane in it against my advice, and the CEL came on due to the knock sensors getting angry. He has since put 91 octane in it and had the code cleared by a mechanic friend of mine; it hasn't come back on to my knowledge.
It has a AEM Brute Force intake, new MAF sensor as of last year, new spark plugs/wires last year. All regular maintenance. Again, the exhaust is bone stock.
Any help is GREATLY appreciated. Gotta get this figured out quick, and I'd like to avoid shelling out $800 bucks for new cats if it turns out that replacing them is the only thing that will fix this.
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