# High NOX on emissions test



## red16vman (Mar 16, 2006)

Just had an Ontario emissions test done and the results are as follows...

ASM2525 TEST (2627 RPM)
HC ppm - 12 Pass (Limit 66)
CO% - 0.01 Pass (Limit .37)
NO ppm - 1944 Fail (Limit 505)

Curb Idle Test
HC ppm - 7 Pass (Limit 150)
CO% - 0.00 Pass (Limit .70)
NO ppm - N/A

Car is a 98 Jetta with the 2.0L ABA, 150k on the ODO
According to these results the engine runs cleaner at higher RPMs, even though the test limits are higher. 

Anyway, with the NOx failure my understanding is that it results generally from lean air/fuel or hot combustion temps. Car has no CEL codes, just fixed the timing as well as replaced the pre-cat O2 sensor within the last month. Car has no cooling issues. What I'm wondering specifically is if there is anything unique about the ABA engine that may cause this to happen.

Tomorrow I will clean out the MAF sensor and check the vacuum lines on the FPR. What else would cause a lean mix or high fuel temps?


My wife and I also notice a very slight hiccup at idle as though it has a misfire but no codes show up as a result. During acceleration/cruising it's smooth but feels a bit under-powered at times. Purely subjective though.


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## ps2375 (Aug 13, 2003)

The car is OBDII and yet you still have to pass a tailpipe test? And with no codes and able to pass the scan test...

I am assuming that the car is stock, since you don't mention any mods. I would be thinking lean and/or timing advanced, but you say the timing has been checked. Cleaning MAF might help, are you able to check the fuel trims to see if it is compensating for a poorly functioning MAF?


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## red16vman (Mar 16, 2006)

Car is bone stock and actually has 220k not 150, I was thinking of a different car for mileage. Anyway, I just fixed the timing about 2 weeks back as well as the pre-cat O2 sensor. I'm going to replace some vacuum lines and clean the maf sensor today, and see if anything is out of whack on the EGR.

In Ontario emissions testing is done through the tailpipe only and there is nothing about the CEL that affects the final results. 

If I'm able to resolve the issue I'll definitely post it in case others have similar issues


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## red16vman (Mar 16, 2006)

Ok I cleaned the MAF today, replaced the vacuum line on the FPR which was badly cracked. I also found a sizeable crack in the exhaust manifold so I patched that up. I'll be going in on monday to drop the car off for another test.

Two questions...

1) Does this car have an EGR, if so, where?
2) If the CO and HC readings are well below limit but the NOx is high, would that suggest the catalytic convertor is fine? 

With the car running fine I'll have no idea that anything changed until the test is done.


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## volkswhisperer (Sep 25, 2006)

Your EGR is at the rear, on the intake manifold. A copper tube runs down to the exhaust manifold.
A non-working EGR could cause high NOX

The leaking FPR vacuum line and the exhaust leak should have caused a rich condition...... weird


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## red16vman (Mar 16, 2006)

I ripped off that heat trap for the intake to examine the exhaust manifold. That's how I discovered the crack. But I don't recall seeing any copper tubing anywhere. Something like that should be pretty obvious I'd imagine. Would anyone have a pic of what it looks like?

EDIT: Upon further research it seems ODBI ABA engines had EGR valves but OBDII did not. Instead they used Secondary Air Injection. 

I've had other MKIII's years back but they were both OBDI and when I owned them I didn't worry about any e-test stuff because I lived in Michigan. I had a MKIV 2.0 that had SAI, but there again I never had to worry because that was in Michigan. So really this is my first experience with an OBDII ABA engine. 

So, can anyone confirm that a Canadian market, 1998 OBDII 2.0L ABA does NOT have an EGR? 

And could I somehow trick the temp sensor to thinking it cooler out so I can richen it up? I just need it to pass once every 2 years.


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## red16vman (Mar 16, 2006)

Did some tests and computer readings today...

1) Ground Fault on CEL. (bulb is burned out)

2) B1S1 O2 sensor reads low voltage. (Lean)

3) Implausible Cam Position Sensor... 

...It brings up this code but I'm not sure why. I fixed the timing and the VAG-COM shows 6 degrees BTDC like it's supposed to but occasionally dips to 5.2 or 5.8 (wonky sensor?) Either way the timing is fine.

Vag-com also shows other sensors all working fine, including MAF. Replaced some vacuum lines, ran seafoam through tank, replaced with 91 octane. Going back for test tomorrow.


If it fails again I'm gonna try a trick with a 25k potentiometer. I'm basically going to run it in-line with a temp sensor to fool the car to into thinking it's colder out to manipulate a richer mix. I'll be able to adjust resistance enough to find a "sweet" spot. 

I'll also be checking fuel pressure too as that may be an issue and can't be measured via Vag-com


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## volkswhisperer (Sep 25, 2006)

The 25k potentiometer works very well. You can lean it out into a misfire or make it slobber rich.


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## red16vman (Mar 16, 2006)

you've done it before then? I just took resister theory and figured 25k would give me enough of a range to work with. I won't be able to lean it out more than it is, i can only make it richer. I plan to wire it in series with the temp sensor, not replace it altogether.


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## red16vman (Mar 16, 2006)

FAIL. 

Had it in for another e-test today after all that seafoam high octane vacuum leak cleaning exhaust patching etc. This time it came out with an even higher NOX than before. Cooling system seems to work just like it's supposed to, temp guage always stops right at the middle on the guage and never goes higher. 

Very frustrating...


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## ps2375 (Aug 13, 2003)

Back the timing off some and see if it will idle.


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## red16vman (Mar 16, 2006)

What timing? Ignition is controlled by the ECM.


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## ps2375 (Aug 13, 2003)

Derp, I forgot this is an ABA with a crank sensor.

High NOX to me means too hot of an exhaust gases, which is either too lean or too much timing advance. I could be wrong,, wish I could be of more help to you....


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## red16vman (Mar 16, 2006)

It runs lean, for reasons unbeknownst to me. I tinkered with some sensors to simulate the engine running colder when in fact it's not, thereby enriching the mixture. We'll see what happens now...


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## caveman1 (May 16, 2011)

i had the same problem on my mk4 jetta. had to replace the cats. you can get used ones for 500- $700.


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## Toronto5.5 (Nov 16, 2009)

caveman1 said:


> you can get used ones for 500- $700.


Thats a joke right?

The source sells used cats with 02 sensors for 100 bucks.


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## caveman1 (May 16, 2011)

hey my mechanic charged me $600 for it. so i'm only quoting what i was charged. for your info i dont deal with him anymore because he also over charged me to replace a clutch ($2200). now i do most of the work myself.


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## red16vman (Mar 16, 2006)

wow. last time I had a shop put in a catalytic converter I think I paid about $200 out the door.

in other news, I haven't taken the car back in, but I drove it around today and I've noticed a remarkable difference in power by fooling the computer into thinking it's colder. This enriches the air/fuel ratio and the car feels way more torquey going up hills, and it runs smoother than before. Although the feeling is entirely subjective, we'll see the results of its next e-test. 

It seems my Intake Air Sensor and my Coolant Temp Sensor aren't reading correctly which has led to the lean mix.

the intake air sensor influences the ignition timing and air/fuel ratio in conjunction with readings from the MAF and barometric pressure sensor, and gets tuned by the O2 sensor. There is a limit to how much the O2 sensor can adjust the air/fuel ratio, and due to it's somewhat slow reaction time it's not a primary indicator on the fuel map.....well at least that's what I've been able to gather.


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## red16vman (Mar 16, 2006)

IT PASSED!

NOX reads 58 now. Well within its 500 limit

What I did...

1. Unplug the Coolant Temp Sensor
2. Unplug with Intake Air Temp Sensor
3. Wire 25k Potentiometer into Intake Air Temp Sensor Plug
4. Set Potentiometer to approximately 6k


It cost me $5 to get the potentiometer at a local electronics supply shop. Best emissions repair ever.


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## ps2375 (Aug 13, 2003)

So, you must have a bad sensor somewhere. I would suspect CTS or O2, as they will have a greater effect than the IAT sensor will.


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## kgvw (Mar 11, 2012)

*more details please*

hey 
can u give me more details how u done it ??
i am having the same problem everything it fine but NOX is failing even though got new catalytic converter..

where did u buy that Potentiomete ???
thanks you


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## Anony00GT (Mar 6, 2002)

Way to go. Instead of discussing the dumb (and illegal) ways to fool an emissions test, how about we discuss proper repair instead?

I wonder if the OP ever fixed his car, or if he's still driving around with a potentiometer wired into the ECT sensor. After all, that works better than using Vag-Com properly to diagnose and repair the problem, right? 

kgvw, start by scanning the car for codes, with Vag-com if possible. Also, post up the test numbers.


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## kgvw (Mar 11, 2012)

Anony00GT said:


> Way to go. Instead of discussing the dumb (and illegal) ways to fool an emissions test, how about we discuss proper repair instead?
> 
> I wonder if the OP ever fixed his car, or if he's still driving around with a potentiometer wired into the ECT sensor. After all, that works better than using Vag-Com properly to diagnose and repair the problem, right?
> 
> kgvw, start by scanning the car for codes, with Vag-com if possible. Also, post up the test numbers.


hey 
i just want to bypass it for now just to get the e-test done(can't live a day without a car) 
and i don't know anyone who has VAG-COM so i am going to buy one .
you know where i can get one for good price ???? ebay ???

when i bought one i will scan it and let everyone know ..hope i will fix it ..


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## Anony00GT (Mar 6, 2002)

The only place to get one:

www.ross-tech.com

You can try a cheap cable from Ebay, but to do anything with it you'll have to buy the $99 VCDS-Lite license from Ross-Tech anyway, and you'll get no hardware support. Many times, even the registered VCDS-Lite won't work due to the crap quality of the made-in-China cables sold on Ebay. 

As for the car, as a certified emission repair technician, it's illegal (and immoral) for me to assist you in circumventing an emission test. Sorry.


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## kgvw (Mar 11, 2012)

I took my car to the mechanic and it turn out to be the O2 sensors


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## mk21.8Tjetta (Jun 3, 2002)

red16vman said:


> IT PASSED!
> 
> NOX reads 58 now. Well within its 500 limit
> 
> ...


Thanks for the info :thumbup:. I will be doing this tomorrow. I'm 4 days passed my temp sticker expiry date and my car failed with the same prob. I'll get the car scanned later...its a mk2 aba swap and the scan port isnt wired in yet :banghead:


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