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Discussion Starter #21
So just an update, I went ahead and picked the car up today. Turns out the dealer had sure enough not even touched the car in a month except to verify that the Adblue was of adequate quality and had only yesterday reached out to VW tech support to see what to do. The SA begrudgingly gave me the reply from VW tech support which spelled out a test for the NOx sensor to be completed, a basic settings procedure to be run, and instructs to replace the NOx catalyst if all else passes. I'll just do this myself with VCDS at this point. Also, no one has ever checked the injector for crystallization so naturally I will do that, too.

I'll reach back out if I have any questions and of course if I am able to pinpoint the problem. Thanks everyone for your help so far!
 

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The CNRB definitely has wisdom and updates learned from the earlier CATA engines. A DPF/SCR delete and tune would take care of all the issues.
I think much hay is made of failures on boards like this. GDI is a 'new' technology (actually, it was on the 50s 300SL and other vehicles) and is going through some teething problems, along with variable vane turbos and a smorgasbord of fuels. I still remember resetting points every thousand miles or so and needing to carry spare condensers.
Gasoline engines have certainly come a long ways and Diesels are becoming more of a corner case.
As far as emissions complexity, I guess it's what you're used to. Both DPF and SCR are fairly straight forward. You seem to be more a victim of incompetent techs than anything. It should have been a one-day fix. If your intake runners clog up on your GDI engine, the head is coming off, so... I guess it's just luck of the draw.
Always use Ceratec every 25k miles on mine, so every 5 oil changes going by 5K OCI. Per my experience with the cam follower, it does in fact adhere to the internals and lasts well more than one oil change.

Maybe sensitive isn’t the right word. Just a lot of complexity in the emissions components compared to gas and a delicate balance I don’t want to upset. Btw ours is actually only 70K miles and it is a 2012 so it has the gen 1 CATA 3.0 tdi. The SCR catalyst has less than 10k on it though as it was replaced as part of the gen 1 3.0 TDI fix.
 

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I wanna say that's hard to believe, but it seemed to be where it was going. There are some really good service departments out there, just not around you apparently.
The test is pretty straightforward; there is absolutely no reason why they wouldn't do it except for willful laziness.
I'd check the injector first. It boggles my mind that wasn't the first thing checked.
So just an update, I went ahead and picked the car up today. Turns out the dealer had sure enough not even touched the car in a month except to verify that the Adblue was of adequate quality and had only yesterday reached out to VW tech support to see what to do. The SA begrudgingly gave me the reply from VW tech support which spelled out a test for the NOx sensor to be completed, a basic settings procedure to be run, and instructs to replace the NOx catalyst if all else passes. I'll just do this myself with VCDS at this point. Also, no one has ever checked the injector for crystallization so naturally I will do that, too.

I'll reach back out if I have any questions and of course if I am able to pinpoint the problem. Thanks everyone for your help so far!
 

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Discussion Starter #24
Agreed, honestly have to say the more I study and understand the diesel emissions system, it's really not all the complicated. Certainly shouldn't take 4 months to diagnose an issue!

Update: Last night I ran the car out for about 30 minutes on the highway and logged the NOx 1 (pre-cat) and NOx 2 (post-cat) sensors and SCR temperature through VCDS. I can share the log should anyone want to see it. The code did not get tripped again, although I don't know if once it's set if it will throw again.

Few notes for diagnostics:
  • The stored fault was tripped with a NOx 2 reading higher than the NOx 1 reading (340 ppm post cat, 283 ppm pre cat). Looks rather fishy.
  • The SCR catalyst temperature hovered around 280-330C on the highway and dropped to 150C after a few minutes of idling.
  • Both NOx sensors read 0 ppm for the first few minutes until the car had heated up a lot. Normal?
  • During the drive on the highway, the pre-cat sensor varied from about 10ppm to 1000ppm depending on whether I was coasting or pressing hard on the throttle. Holding constant speed with slight throttle it seemed to hover in the 300ppm range. To be expected, correct?
  • The post-cat sensor stayed at 0ppm a minute or two longer after the pre-cat began giving actual readings. It then jumped to a steady -22ppm for a minute or two, then to 1650ppm for another minute or two, then gradually began to drop to steady readings that varied between about 10ppm to -10ppm the whole drive, except when I let off the throttle and it would spike a little. For the most part it stayed no more than 10% of the pre-cat sensor but would occasionally spike to 40-50% for a time stamp or two.
-Long term adaptation for reducing agent was 1.04, so within spec.

After returning, I ran the SCR catalyst efficiency test and the Adblue error and countdown disappeared. Going to drive the car some today to see if they come back. Whatever the problem is, it seems to be borderline/sporadic. Thoughts? Definitely will check the injector for crystallization but I am leaning towards a lazy post-cat NOx sensor.

Also of note, I had a few instances of P102C "Torque Limitation Due to Fuel Temperature" logged. It's a priority 6 fault so no MIL thrown, but still concerning. Fuel temp varied between 76C to 80C on the highway. Temperature in the 90's F out and A/C running. Anyone seen this before?
 

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Discussion Starter #25
One more update:

Driven 50 miles and Adblue errors have not returned yet. I tested the fuel temperatures and found about 50-55C while idling. Revving up to 2K+ RPM and the temperature climbs to 70-80C. When on the highway, coasting at 1.5K to 2K, the temperature climbs to 70-80C the same as when stopped, but begins to drop rapidly when I step hard on the throttle. Could this be a fuel return issue or is it just normal operation and a side effect of it being in the 90's F outside?

Again, it's P102C "Torque Restriction due to Fuel Temperature" being thrown and it's a low level priority 6 fault so no MIL thrown for it.
 

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I'll take a stab at some of this.
For the pre/post NOx sensors, I don't think it's possible for what the sensors are representing to happen. Most likely the sensors were re-installed backwards or at least one is faulty.

No comment on the SCR temp; I'm not familiar enough to comment.

0 ppm NOx at startup is normal. NOx is produced by high-temperature combustion of organic material (such as any fossil fuel). Gasoline combustion occurs at lower temperatures and so has lower NOx emissions, while Diesel combustion occurs at much higher temperatures (promoting efficiency). On startup, when combustion and exhaust temperatures are relatively low, you would not expect to see NOx. I also don't think the SCR system works at low temperatures.

I'm not sure of the exact values; I haven't looked at mine. Roughly speaking, NOx is going to be higher under higher engine loads, and lower under low/steady engine loads. Your observations seem to correlate to this.


Post cat would be last to warm up, so this behavior makes sense. Again, I'm not sure of the values. Not sure how you can get a negative value- dunno if it's a symptom of a bad sensor or just the way the system interprets the value from the sensor.

Yeah, the system seems to be working. They might have actually addressed the issue so they could bill VW.

How much fuel do you have in your tank?

Agreed, honestly have to say the more I study and understand the diesel emissions system, it's really not all the complicated. Certainly shouldn't take 4 months to diagnose an issue!

Update: Last night I ran the car out for about 30 minutes on the highway and logged the NOx 1 (pre-cat) and NOx 2 (post-cat) sensors and SCR temperature through VCDS. I can share the log should anyone want to see it. The code did not get tripped again, although I don't know if once it's set if it will throw again.

Few notes for diagnostics:
  • The stored fault was tripped with a NOx 2 reading higher than the NOx 1 reading (340 ppm post cat, 283 ppm pre cat). Looks rather fishy.
  • The SCR catalyst temperature hovered around 280-330C on the highway and dropped to 150C after a few minutes of idling.
  • Both NOx sensors read 0 ppm for the first few minutes until the car had heated up a lot. Normal?
  • During the drive on the highway, the pre-cat sensor varied from about 10ppm to 1000ppm depending on whether I was coasting or pressing hard on the throttle. Holding constant speed with slight throttle it seemed to hover in the 300ppm range. To be expected, correct?
  • The post-cat sensor stayed at 0ppm a minute or two longer after the pre-cat began giving actual readings. It then jumped to a steady -22ppm for a minute or two, then to 1650ppm for another minute or two, then gradually began to drop to steady readings that varied between about 10ppm to -10ppm the whole drive, except when I let off the throttle and it would spike a little. For the most part it stayed no more than 10% of the pre-cat sensor but would occasionally spike to 40-50% for a time stamp or two.
-Long term adaptation for reducing agent was 1.04, so within spec.

After returning, I ran the SCR catalyst efficiency test and the Adblue error and countdown disappeared. Going to drive the car some today to see if they come back. Whatever the problem is, it seems to be borderline/sporadic. Thoughts? Definitely will check the injector for crystallization but I am leaning towards a lazy post-cat NOx sensor.

Also of note, I had a few instances of P102C "Torque Limitation Due to Fuel Temperature" logged. It's a priority 6 fault so no MIL thrown, but still concerning. Fuel temp varied between 76C to 80C on the highway. Temperature in the 90's F out and A/C running. Anyone seen this before?
 

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Well if anyone knows of a good dealer for TDI warranty work or even an independent TDI tech in the MD area, please let me know!

I've been reading up on the issues and the system itself and I've seen the crystallized adblue problem hinted at numerous times. I would certainly check it out if/when I get the car back. Thanks for the suggestion.
Just caught up w/this thread. I echo WolverineFW's observations. Had your same symptoms back around 155k. It first manifest when I was 2000 miles from home. Not ideal. A dealer or private shop with TDi experience is essential if you don't fully DIY. My local dealer has extensive TDi experience and solid techs, and was able to drill into the problem with VWofA very quickly. I had crystallization, but they also found the DEF injector and supply line had been damaged and required replacement. I don't know what caused it, but maybe running hard into headwinds across the Dakotas and Montana? (I burned through the entire tank of DEF in 3k miles & normally get 10k.) In my case, VWofA and my dealership agreed to absorb half the repair cost as well, even though I'm well past warranties. I know it's not everyone's experience (and hasn't always been mine), but I've been totally pleased with my dealer experience and have serviced there since new.
 

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So just an update, I went ahead and picked the car up today. Turns out the dealer had sure enough not even touched the car in a month except to verify that the Adblue was of adequate quality and had only yesterday reached out to VW tech support to see what to do. The SA begrudgingly gave me the reply from VW tech support which spelled out a test for the NOx sensor to be completed, a basic settings procedure to be run, and instructs to replace the NOx catalyst if all else passes. I'll just do this myself with VCDS at this point. Also, no one has ever checked the injector for crystallization so naturally I will do that, too.

I'll reach back out if I have any questions and of course if I am able to pinpoint the problem. Thanks everyone for your help so far!
Hey Woody,
I had the same problem with my 12 Touareg TDI and the VW dealer in Fairfax on route 50 was very helpful and they had a VW engineer come out and try to fix my vehicle. It took awhile as well but in the end fixed it. They replaced everything and I did get a code again but they fixed it again and I haven’t had a problem with it yet. It happened every time I had to replace ad blue and when I did fill it up it would throw the codes. But this time around after filling ad blue it was good to go. So if you live in the Maryland area you may want to go to Fairfax VW on route 50 and speak with DJ or Leon. Both are good people and will get you taken care of. They put me in top of the line tiguans or golf all tracks when I had to get a loaner. I waited for a couple months as well when it was in the shop. So I know exactly what your going through. Just wanted to let you know about Fairfax dealership and my experience with them. They may be able to help you out. Good luck!
 

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Discussion Starter #30
Thanks for the replies everyone!

So my current theory is that after replacing the ECM, which was the dealer's first guess at the problem (for reasons I cannot decipher), they did not run the adaptations for the Adblue system properly. The reason I guess this is because the errors began to arise immediately after this replacement and they had never come on before. So until the errors return (and fingers crossed they won't! This is the first time I've given it a good drive since April without the Adblue light coming on), I'm just going to leave it alone and enjoy the vehicle.

As for the fuel temperature, RocketTech, my fuel tank is full. I've heard you don't want to run these low (or any car really).
 

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I know my VW dealer maint manager said flat out audi and porsche was paying more for the diesel mechanics, so they all left
My dealer services all three brands and the techs are completely separate. I'm not even sure if they eat lunch together.

Nothing is more frustrating than bringing your car in for warranty work, have it "repaired", bring it in again for the same failure, have it "repaired" again, and then digging in and fixing it right yourself. Ask me how I know. At least my dealer never left the car in the back lot for a month hoping it would go away.
 

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Discussion Starter #32
Just another update, Adblue faults still aren't returning. Really looks like all the car needed was a reset of the SCR calibration. And in a month they couldn't do this at the dealer...

As for the fuel temperature "soft" error, we just had a storm move through and it bumped the temperature down from the 90's F to the 70's. Did a run on the highway and sure enough fuel temperatures remained in the 60's C for the most part and the fault code was not tripped. So at the moment assuming the hot weather was at fault for the 75-80 C temps I was seeing the other day.

Anyone else ever experienced this?
 

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My catalyst efficiency codes on mine slowly got more and more frequent. I was just clearing the engine light at first and ignoring it. Eventually became a problem with the Adblue countdown to no start.

Check your SCR injector. It is easy remove and easy to clean. I carefully used a small pick to clean mine and the mounting hole.
Just another update, Adblue faults still aren't returning. Really looks like all the car needed was a reset of the SCR calibration. And in a month they couldn't do this at the dealer...

As for the fuel temperature "soft" error, we just had a storm move through and it bumped the temperature down from the 90's F to the 70's. Did a run on the highway and sure enough fuel temperatures remained in the 60's C for the most part and the fault code was not tripped. So at the moment assuming the hot weather was at fault for the 75-80 C temps I was seeing the other day.

Anyone else ever experienced this?
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Discussion Starter #34
Bump with new update:

After a week and about 4-500 miles of driving, the MIL finally came back. Interestingly, the countdown did not return, though. But the codes are P20EE for NOx catalyst efficiency and (wait for it) P229F for implausible signal from the rear NOx sensor. So exactly as I expected, a wonky sensor on the way out. I would replace myself, but for $450 I will probably just take it to a different dealer and hope for the best with service.
 

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Too bad it wasn't the end of it.
Was the SCR injector ever checked?
Hopefully you have better luck with the new dealer.
Bump with new update:

After a week and about 4-500 miles of driving, the MIL finally came back. Interestingly, the countdown did not return, though. But the codes are P20EE for NOx catalyst efficiency and (wait for it) P229F for implausible signal from the rear NOx sensor. So exactly as I expected, a wonky sensor on the way out. I would replace myself, but for $450 I will probably just take it to a different dealer and hope for the best with service.
 

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Bump with new update:

After a week and about 4-500 miles of driving, the MIL finally came back. Interestingly, the countdown did not return, though. But the codes are P20EE for NOx catalyst efficiency and (wait for it) P229F for implausible signal from the rear NOx sensor. So exactly as I expected, a wonky sensor on the way out. I would replace myself, but for $450 I will probably just take it to a different dealer and hope for the best with service.
I had multiple different NOX sensor codes with the efficiency code. None of the sensors were bad.



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