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CO measured 0 and high NO = Failed smog

Tiny
ANTNIDA
  • MEMBER
  • 2001 LEXUS IS 300
  • 215,000 MILES
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
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Friday, October 4th, 2013 AT 4:32 PM

11 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
So. It failed. For. High nox reading?
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Friday, October 4th, 2013 AT 4:35 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,938 POSTS
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.
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Friday, October 4th, 2013 AT 4:36 PM
Tiny
ANTNIDA
  • MEMBER
  • 6 POSTS
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.
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Friday, October 4th, 2013 AT 9:44 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
If you have high nox Howe is the egr valve working?
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Friday, October 4th, 2013 AT 9:48 PM
Tiny
ANTNIDA
  • MEMBER
  • 6 POSTS
Hi saturntech9,

This car has VVT-I in place of EGR so there is no EGR.
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Friday, October 4th, 2013 AT 9:57 PM
Tiny
SATURNTECH9
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What are your NOx readings measured on your car and what is maxuim allowable NOx readings for your Car.
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Monday, October 7th, 2013 AT 9:21 AM
Tiny
ANTNIDA
  • MEMBER
  • 6 POSTS
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
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Monday, October 7th, 2013 AT 8:28 PM
Tiny
SATURNTECH9
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So before the o2 sensors were replaced the NOx readings were only 10 at 15mph and 74 at 25mph?
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Monday, October 7th, 2013 AT 11:28 PM
Tiny
ANTNIDA
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That's correct.
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Tuesday, October 8th, 2013 AT 8:32 AM
Tiny
SATURNTECH9
  • MECHANIC
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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?
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Tuesday, October 8th, 2013 AT 9:56 AM
Tiny
ANTNIDA
  • MEMBER
  • 6 POSTS
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.
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Tuesday, October 8th, 2013 AT 11:33 AM

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