CO measured 0 and high NO = Failed smog

2001 LEXUS IS 300
215,000 MILES
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ANTNIDA
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The first time I brought my car in for smog check it fail functional test because CEL was on for O2 sensors (I did not know this because the check engine light bulb was burned out), I replaced the oxygen sensors, CEL light bulb and cleaned the MAF with MAF cleaner bought from auto parts store. The car ran great and accelerate very well, 500 miles later I took it in for a retest and it Fail the Emissions Test (which passed before the o2 sensors replacement). I checked all the hoses and I didn't missed anything. I only take a part the MAF sensor and the intake hose to get access to the o2 sensors, replaced it after o2 sensors repair. Not sure how to diagnose this one since it was passed before and no CEL at the moment. Any suggestion would be appreciated.

Thanks
Oct 4, 2013 at 4:32 PM
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SATURNTECH9
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so.it failed.for.high nox reading?
Oct 4, 2013 at 4:35 PM
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MHPAUTOS
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You need to get the emissions tested with a 5 gas analyser, this will probably be a tune related problem, it may be lean due to a vacuum leak or rick due to a faulty spark plug or injector, start here.
Oct 4, 2013 at 4:36 PM
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ANTNIDA
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Hi saturntech9,

Yes, it failed for high nox reading.

mhpautos,

I'll concentrate on finding vacuum leak first because there was no issue with emission during the first smog test, it happened after I replaced the o2 sensors, so it could be due to me causing a leak taken the intake hose and MAF sensor out to make room to get to the o2 sensors.
Oct 4, 2013 at 9:44 PM
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SATURNTECH9
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if you have high nox Howe is the egr valve working?
Oct 4, 2013 at 9:48 PM
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ANTNIDA
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Hi saturntech9,

This car has VVT-I in place of EGR so there is no EGR.
Oct 4, 2013 at 9:57 PM
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SATURNTECH9
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What are your NOx readings measured on your car and what is maxuim allowable NOx readings for your Car.
Oct 7, 2013 at 9:21 AM
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ANTNIDA
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Smog retest after o2 sensors replaced (passed visual & Functional Check)
NOx reading,
Max Meas
15 MPH 419 1122
25 MPH 706 1328

CO reading
Max Meas
15 MPH .48 0.00
25 MPH .46 0.00

First Smog test (failed functional check for o2 sensors)
NOx reading,
Max Meas
15 MPH 419 10
25 MPH 706 74

CO reading
Max Meas
15 MPH .48 0.47
25 MPH .46 0.43



Oct 7, 2013 at 8:28 PM
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SATURNTECH9
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So before the o2 sensors were replaced the NOx readings were only 10 at 15mph and 74 at 25mph?
Oct 7, 2013 at 11:28 PM
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ANTNIDA
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That's correct.
Oct 8, 2013 at 8:32 AM
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SATURNTECH9
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That really doesn't make a whole lot of sense.Were the o2 sensors bad is that why they were replaced?
Oct 8, 2013 at 9:56 AM
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ANTNIDA
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Yes, they were bad. ECL throw code, P0171,P0174,P0130,P0133,P0150,P0153.

After replacing the 2 oxygen sensor only P0171 and P0174 was left, after the MAF sensor was cleaned with MAF cleaner those 2 codes was gone and haven't comeback, now the car ran so smooth, no more sluggish acceleration issue.
Oct 8, 2013 at 11:33 AM