failed emissions testing (1 Viewer)

[semlin]

So I failed our gov't emissions testing on the NOX by nearly 4 times the limit, and I was very high but a pass on the others compared to average readings for this vehicle. Does anyone know anything about diagnosing this stuff? I am thinking 02 sensor, but wouldn't that throw a code? I have never had a code come up since I bought the truck last year (would an old code still be stored in the little black box?).

Anyway here are the results in g/km if anyone can tell much from them. I guess you multiply by 1.6 to get g/mile if thats what you guys use down south.

maximum vehicle reading average
Hydrocarbons 0.99 0.6756 0.1655
Carbon monoxide 12.43 9.9628 2.6518
NOX 1.55 5.3381 1.4807

I guess I am not alone in failing NOX. The average reading for NOX on this vehicle is within .07 of a fail.

 

[Brentbba]

No expert, but O2 sensors would be my guess based on the exact thing happening to me several years ago. Everything except O2 passed with flying colors but was the same 4x over as you. Dealer had botched the replacement of O2 sensors IMHO (just did this myself and can't see how they could have screwed it up). Dealer claimed something about the loose wiring, retested and passed easily. I had no code either. Good luck. Next test I had to go to a test only station as beast had been labeled a gross polluter as a result of the past failed oxygen test. Due again next year. We'll see.....

 

[landtank]

man it's been a while, all I can remember is the teacher stressing is the air cleaner. How's your air filter, plugs and general ignition system?

 

[Gumby]

NOX is caused by high temps during combustion. A lean engine will run hot enough to raise NOX so an O2 causing a lean run condition can do it too. Vacuum leak or cooling system problem could do it, but you'd probably see other problems. No EGR can cause it as well.

 

[semlin]

I have a K&N air filter new this summer and the dolgarn platinum plugs which I should probably ditch if I wasn't afraid of reaching plug #6. No idea about rest of ignition.

Gumby, shouldn't the problems you describe all produce a code? I doubt a cold cat would cause such a high fail.

 

[Gumby]

Try this link. I don't know if your cat would make a difference one way or the other, but if you have a lot of fuel in the cat, it might burn too hot causing NOX. I'm not really sure though.

http://www.autoshop101.com/forms/h55.pdf

 

[landtank]

93s only have the O2 senser in front of the cats not fore and aft as the OBDIIs do. Your system is blind too what goes on in the cat, if I'm not mistaken

 

[Pokemon]

Semlin,
I would start by checking the EGR system first. It directly relates to Nox readings if it is not functioning properly. Then look elsewhere as others here already have mentioned. Good luck.

 

[97tlc]

I failed emissions also and got a 401 error code. Turned out to be EGR. EGR failure causes high NOX readings I believe. Even though MIL (check engine light) is not on, there could be a error code stored in memory. In CA, you can pass emissions but still fail if there is a error code in memory.

 

[Riley]

Hey Simon, During the tests do they connect up to the ODB connector?

 

[Beowulf]

97tlc,
Please give us the specifics on your 401 code including exactly what was replaced and how you fixed the problem.
-B-

 

[IdahoDoug]

Semlin,

Does your check engine light up when you turn the key on and first start the car? Maybe the bulb's out and you've got a code?

DougM

 

[97tlc]

Stealer charges $75 to do diagnostic check. P0401 comes up and they say I need 1)90910-12043 and 90910-12079, vacuum swithcing valves and 2)25870-66011 EGR valve assy ($200 in parts) + $400 labor. I say no thanks. Buy the parts but only EGR is accessable so I change just that and the check engine light goes out. Return unused parts and reset light with code reader. Drive for a day and everything is okay and I pass smog with flying colors.

 

[landtank]

In my business we call that the SHOTGUN approach. Stand back, load up with everything it probably is, could be and next to and blast it in. Beleive it or not it can and will backfire on occation.

 

[semlin]

Hey folks, I am also wary of the shotgun approach. I have booked it into a dealer for a diagnosis for a flat one hour fee. For that they will test the egr, o2 and presumably timing etc... depending on what they tell me I will take the next step myself. No way do they get turned loose.

 

[Gumby]

[quote author=97tlc link=board=2;threadid=8319;start=msg71404#msg71404 date=1070588678]
Stealer charges $75 to do diagnostic check. P0401 comes up and they say I need 1)90910-12043 and 90910-12079, vacuum swithcing valves and 2)25870-66011 EGR valve assy ($200 in parts) + $400 labor. I say no thanks. Buy the parts but only EGR is accessable so I change just that and the check engine light goes out. Return unused parts and reset light with code reader. Drive for a day and everything is okay and I pass smog with flying colors.
[/quote]

having passed smog, you might have found the problem. Unfortunately, P0401 is a two trip logic code. The ECM needs to see all of the sensors read to certain perameters on two seperate start ups. You could drive it for months before you complete two "trips" Not to jinx you, but your problem is not assuredly fixed. In fact, posting that your problem is repaired seems to be the trigger that makes the light turn back on.

 

[Beowulf]

97tlc,

Yep, sounds familiar. Went 4 months after the EGR valve was replaced then the P0401 returned again and by then it was a hard failure. Every 2 trips no matter what. This happened shortly after I shot off my mouth a few times saying that the P0401 was gone.

-B-

 

[sea2skydad]

Simon,

If this becomes one of those nagging, obsessive problems a different approach would be to change your mailing address to say Squamish(outside the GVRD)where we enjoy emissions exemptions, cheaper insurance, some wicked wheelin' and... I digress. I know others who do it, namely my brother with his HJ60.

 

[semlin]

So went through my FSM more carefully last night to figure out what diagnostic testing is done on the EGR and o2 sensors. I already have a digital multimeter so it looks to me like I could do all the testing if I just bought a vacuum gauge and bent a paper clip. Am I fooling myself? I would rather spend $100 and have a vacuum gauge forever than pay that to have a possibly lazy toyota wrench tell me to replace everything. However, I also thought those big computer thingies could work wonders on diagnosing this stuff. Why are they not mentioned in the FSM? What does the shop diagnosis actually do?

 

[Gumby]

If it's a Toyota shop they have the scan tool that should be able to drive the EGR VSV and they can read the temp sender values with it as well. That would make the job a lot easier. That specfic tool is incredibly expensive, so you are probably stuck with the ohm meter and vacuum guage. That's all a non-dealer would use anyway.