I have the truck test it 2 times, the first I pass emission but I fail oxigen sensors. On the second test I pass everything but I fail the emission test, the HC and NO readings are to high. What can I do to pass it.
Fist i would like you to post the year make and model of the truck along with the HC ppms and NOX ppm it would be very helpful but high hc and nox can be attributed to a faulty EGR system nox is produced when the combustion chamber temperature gets too high so a small amount of exhaust is cycled back into the air stream to help cool them there are other causes but without looking at the levels its much harder to say
SOURCE: ASM 2525 NO ppm TAILPIPE EMISSIONS failure
have you had the the engine codes pulled and reset?
and if so what are your engine codes?
i dont know of any car that will pass emissions test with the engine light on.
we cure your trouble that caused your engine light to come on and you will pass your test.
later
paul
SOURCE: My 1991 4runner failed emissions test with high CO and HC levels.
Not sure, but did you replace the oxygen sensors. Is your catalytic converter still good?
SOURCE: 1991 Honda Accord LX failed emission test on smog
not enough info. Typically, CO and HC together can be the result of poor fuel control or misfire, or worn components such as O2 sensor or catalytic converter, but without more data, repair recommendations are likely to waste money and not achieve success.
SOURCE: high nox fail smog test any remedies? 99
NOX is created when the internal combustion temperature gets to high.The egr system uses burnt exhaust gases to line to cylinder walls.The purpose of this is decrease internal combustion temperature therefore reducing the amount of NOX created.Would look to a possible egr malfunction usually they will trigger the check engine light but not always.The 4.3L has been known to have issues with carbon buil up in the egr and the egr pintle not open and closing properly.
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