T6 AdBlue/DPF Nightmare - Garage Told Me to Scrap It, But It Drives Fine?!

[KPanch98]

I’m absolutely stumped and could really use some help from anyone who knows the T6 inside out.

I’ve had my 2017 VW T6 BlueMotion DSG 2.0 TDI (117,500 miles) or about a year, spent the first 6 months (and around £6K) converting it into a camper, and since using it regularly it's been throwing P20EE (SCR NOx Catalyst Efficiency Too Low) and P204F (Reductant System Performance Bank 1) codes at me on and off.

VW Main Dealer already did a software update and replaced a split EGR pipe, but the EML came back after about 1,000 miles. The van runs great, starts well, drives smoothly, no smoke and no noticeable loss of power. Sometimes I’ll get the “No engine start in 650 miles” AdBlue warning, but it clears itself mid-drive.

Yesterday, a local garage said the NOx sensor was covered in soot and there was soot inside the exhaust, so they believe the DPF must be cracked, which they say is likely because of excessive engine crankcase pressure, potentially from worn piston rings (they cannot be sure of this without taking the engine apart - which they do not advise due to cost). Note I have not had any DPF related EML's, which I find strange if it has cracked. Unless a previous owner has tampered with something here...

They’ve basically said that as well as the whole DPF & SCR systems needing replacing, the engine should also be replaced. They’ve suggested I cut my losses and get rid of the van rather than spending this ££ on it.

It all doesn’t sit quite right with me. I’m struggling to understand how “engine pressure” (which I haven't seen any evidence for) could crack a DPF or why it would only cause these AdBlue/NOx codes.

Has anyone here had similar symptoms (P20EE / P204F / sooty NOx sensor)?

Feels crazy to scrap the van when it’s driving just fine, and I've put so much time and effort into the conversion! Any advice, real-world experience, or recommendations for a trusted VW expert who could help me out would be awesome.

I’m completely lost at this point and just want to figure out what’s actually wrong, and what the best next steps are before throwing in the towel.

Thanks so much in advance!

VCDS and the report from the dealer attached.

 

[mmi]

there was soot inside the exhaust

Is there actually soot in the tailpipe?

VW Main Dealer already did a software update

Within your ownership? Running original VW software - no remaps?

it's been throwing P20EE (SCR NOx Catalyst Efficiency Too Low) and P204F (Reductant System Performance Bank 1) codes at me on and off.

Have you been clearing the faults - as they both show only frequency=1?

Do you get the below often - as it was now intermittent and not confirmed (=was not at fault when scanned)?

SCR systems needing replacing

How did the garage conclude that?

 

[KPanch98]

@mmi - Thanks for your response!

Yes there was soot in the tailpipe. Also, yes running original VW software, no remaps. They did their software update for me a few months back at the main dealer.

I have had P20EE come up for me around 5-6 times, which I have been clearing, but P204F has only come up for me once.

Not sure how the garage concluded the SCR system needed replacing, as only the NOx sensor was covered in soot apparently. This makes me want to get a second opinion?

I should also mention that the EGR pipe had previously split (but was replaced around 1500 miles ago), which I think could be another explanation for the soot in the tailpipe and covering the NOx sensor. Now this is fixed, perhaps it just needs a good clean?

 

[mmi]

P20EE is only indication of excessive NOx level in the exhaust - just a monitoring "circuit" - not even pinpointing the NOx sensor itself being at fault. Not sure if soot covering would make it read "high" NOx levels.

So just need to figure out why the NOx levels are too high. The AdBlue system is there to reduce the NOx - would need to check that AdBlue is actually injected. Check the AdBlue injector?

P204F has only come up for me once.

Well, a kind of good news.

I should also mention that the EGR pipe had previously split (but was replaced around 1500 miles ago), which I think could be another explanation for the soot in the tailpipe and covering the NOx sensor.

No, doesn't explain soot after the DPF.
Anyways, there is a dedicated sensor to detect excessive soot in the exhaust - would trigger a separate fault code.

They did their software update for me a few months back at the main dealer.

Why the software was updated? Because of P20EE fault? Any difference?

Please post also full engine data header (above the P204F fault) of VCDS report.

 

[DXX]

I’m absolutely stumped and could really use some help from anyone who knows the T6 inside out.

I’ve had my 2017 VW T6 BlueMotion DSG 2.0 TDI (117,500 miles) or about a year, spent the first 6 months (and around £6K) converting it into a camper, and since using it regularly it's been throwing P20EE (SCR NOx Catalyst Efficiency Too Low) and P204F (Reductant System Performance Bank 1) codes at me on and off.

VW Main Dealer already did a software update and replaced a split EGR pipe, but the EML came back after about 1,000 miles. The van runs great, starts well, drives smoothly, no smoke and no noticeable loss of power. Sometimes I’ll get the “No engine start in 650 miles” AdBlue warning, but it clears itself mid-drive.

Yesterday, a local garage said the NOx sensor was covered in soot and there was soot inside the exhaust, so they believe the DPF must be cracked, which they say is likely because of excessive engine crankcase pressure, potentially from worn piston rings (they cannot be sure of this without taking the engine apart - which they do not advise due to cost). Note I have not had any DPF related EML's, which I find strange if it has cracked. Unless a previous owner has tampered with something here...

They’ve basically said that as well as the whole DPF & SCR systems needing replacing, the engine should also be replaced. They’ve suggested I cut my losses and get rid of the van rather than spending this ££ on it.

It all doesn’t sit quite right with me. I’m struggling to understand how “engine pressure” (which I haven't seen any evidence for) could crack a DPF or why it would only cause these AdBlue/NOx codes.

Has anyone here had similar symptoms (P20EE / P204F / sooty NOx sensor)?

Feels crazy to scrap the van when it’s driving just fine, and I've put so much time and effort into the conversion! Any advice, real-world experience, or recommendations for a trusted VW expert who could help me out would be awesome.

I’m completely lost at this point and just want to figure out what’s actually wrong, and what the best next steps are before throwing in the towel.

Thanks so much in advance!

VCDS and the report from the dealer attached.

View attachment 307493

View attachment 307494

View attachment 307495

When the dealer said to ‘get rid of it’ how did you deduce ‘scrapping it’?

 

[KPanch98]

When the dealer said to ‘get rid of it’ how did you deduce ‘scrapping it’?

Sorry, chose the wrong word here. He did not tell me to scrap it, but suggested I cut my losses by getting rid. Apologies.

 

[KPanch98]

P20EE is only indication of excessive NOx level in the exhaust - just a monitoring "circuit" - not even pinpointing the NOx sensor itself being at fault. Not sure if soot covering would make it read "high" NOx levels.

So just need to figure out why the NOx levels are too high. The AdBlue system is there to reduce the NOx - would need to check that AdBlue is actually injected. Check the AdBlue injector?


Well, a kind of good news.


No, doesn't explain soot after the DPF.
Anyways, there is a dedicated sensor to detect excessive soot in the exhaust - would trigger a separate fault code.


Why the software was updated? Because of P20EE fault? Any difference?

Please post also full engine data header (above the P204F fault) of VCDS report.

Thanks for this @mmi The software was updated when I took it to VW for the P20EE fault. This seemed to buy me a bit more time before the EML came back, but it still did. Usually I was getting it around every few hundred miles after clearing but after the update it took around 1000 miles I would guess.

I am confused as to why no fault codes are triggering for the soot, but when the mechanic at the local garage put his finger in the tailpipe it came out black. Could the previous owner have remapped or tampered with the physical DPF without me knowing? Apologies if this is a silly question, I'm very new to all of this!

Here's the data above the fault code for you

Control Module Part Number: 04L 906 056 KG HW: 04L 907 445
Component and/or Version: R4 2.01 TDI H02 6168
Software Coding: 00254010432501090000
Work Shop Code: WSC 35110 790 50316ASAM
Dataset: EV_ECM20TDI03004L906056KG 004013 (VN75)
VCID: 7CA2FDBD96608A6AD2B-8028

 

[DXX]

Sorry, chose the wrong word here. He did not tell me to scrap it, but suggested I cut my losses by getting rid. Apologies.

Well there’s plenty of lemons on the market, I can think of a few acquaintances who’ve bought cars privately recently without checking for fault codes.

 

[mmi]

I am confused as to why no fault codes are triggering for the soot, but when the mechanic at the local garage put his finger in the tailpipe it came out black.

Either not enough soot to trigger the fault. Also if you would rarely drive more than 30 minutes - the check for soot is done periodically for hot engine only.

Could the previous owner have remapped or tampered with the physical DPF without me knowing?

I would say the VW software would have picked it up.

Some observations on soot detection in below

Post in thread '[T6_measured] Monitoring DPF regeneration, DPF condition, EGR operation'

6 Aug 2023

Indeed the particle sensor is registering something...

Did you also get any of the faults codes?

P226D00 - Particle filter damaged or substrate missing Intermittently
P24B100 - Particle sensor measurement electrode short-circuit to positive pole Intermittently
P24B000 - Particle sensor measurement electrode short-circuit to ground Intermittently

Zoomed in​

Well below the 10 minutes...

• mmi

• 

Control Module Part Number: 04L 906 056 KG HW: 04L 907 445
Component and/or Version: R4 2.01 TDI H02 6168

Yes, it's up-to-date.
However, interestingly there seems to be a quite recent update.

Welcome to VAG-Flashinfo!

VAG Flashfiles Informations - Version check of VAG ECUs - Update check for Audi, Seat, Skoda and Volkswagen

vag-flashinfo.de

 

[KPanch98]

Either not enough soot to trigger the fault. Also if you would rarely drive more than 30 minutes - the check for soot is done periodically for hot engine only.


I would say the VW software would have picked it up.

Some observations on soot detection in below

Post in thread '[T6_measured] Monitoring DPF regeneration, DPF condition, EGR operation'

6 Aug 2023

Indeed the particle sensor is registering something...

Did you also get any of the faults codes?

P226D00 - Particle filter damaged or substrate missing Intermittently
P24B100 - Particle sensor measurement electrode short-circuit to positive pole Intermittently
P24B000 - Particle sensor measurement electrode short-circuit to ground Intermittently

Zoomed in​

Well below the 10 minutes...

• mmi

• 

Yes, it's up-to-date.
However, interestingly there seems to be a quite recent update.

Welcome to VAG-Flashinfo!

VAG Flashfiles Informations - Version check of VAG ECUs - Update check for Audi, Seat, Skoda and Volkswagen

vag-flashinfo.de

View attachment 307557

Thanks for your response @mmi - I regularly do long runs in the van so no idea why I haven't had any had any soot-related faults. Only P20EE and P204F.

My current thinking is that the adblue injector should be checked, and then perhaps the DPF should be replaced, as the soot in the exhaust must imply some kind of breakage. But I will take it to a VAG specialist to try and confirm this for me.

Is there anything else you suggest or do you see any reason to suspect the engine itself might be on its way out? I know it's difficult to tell from this limited information, but any hunches would be super useful, as I just don't know whether I should cut my losses at this stage or if there is still some hope. Many thanks!

 

[mmi]

My current thinking is that the adblue injector should be checked,

Yes, agreed. To get better idea certainly would like to see a few measurements re AdBlue injection and NOx level using dignostic tool.

perhaps the DPF should be replaced

Wouldn't rush into that as long as the ECU doesn't complain. Again, it would be interesting to see a few related measurements to evaluate condition of the DPF

do you see any reason to suspect the engine itself might be on its way out?

No, not really because

The van runs great, starts well, drives smoothly, no smoke and no noticeable loss of power.

and because

DPF must be cracked, which they say is likely because of excessive engine crankcase pressure,

doesn't make any sense. There is no connection from crankcase to exhaust and DPF.
Also would be interesting to how much is excessive pressure. There is naturally some pressure in crankcase.

excessive engine crankcase pressure, potentially from worn piston rings

Worn piston rings would show also other symptoms - e.g. poor starting, juddery idling, engine oil consumption, etc.

any hunches would be super useful,

it's difficult to tell from this limited information

Is there anything else you suggest

Perhaps VCDS purchase

Ross-Tech VCDS (VAG-COM) Packages :: Gendan Automotive Products

 

[KPanch98]

Thank you @mmi - really appreciate you helping me to dig into this

What's the best way to get those DPF-related measurements?

One thing I forgot to mention, which may be important, is that another reason for his 'excessive pressure' analysis is that when he opened the oil cap under the bonnet with the engine running, it was clear there was some air coming up through this pipe. I know some of this is normal, but I'm not sure whether the amount of air coming through falls into that category of being 'normal' or if it was more severe. If i unscrew the oil cap and rest it back on top of the oil inlet, it will rattle and rise a little. Maybe I can get a video of this? Should I seek to get a compression test carried out to check this?

Also (another thing I've just remembered) sometimes, perhaps every 4th/5th time starting the van, it takes a little longer to turn over (perhaps 2 seconds), but it always does AND then proceeds to drive perfectly fine.

Not sure if this extra info is useful, but let me know if it is!

Next steps I'm thinking are to do a compression test - if this comes back okay confirming the engine is still in good shape, I'll get the Adblue injector checked out!

 

[mmi]

If i unscrew the oil cap and rest it back on top of the oil inlet, it will rattle and rise a little.

Sounds normal to me.

Should I seek to get a compression test carried out to check this?

I wouldn't.

perhaps every 4th/5th time starting the van, it takes a little longer to turn over (perhaps 2 seconds)

Should I seek to get a compression test carried out to check this?

Hmm... 2 seconds is very long time to crank - makes me wonder what's the "normal" then as it should pretty much instant start-up (about 0.5 seconds cranking).
Poor compression surely would affect starting but there are quite a few other things to rule out before - simply using proper diagnostic tool.

What's the best way to get those DPF-related measurements?

Cracked DPF? Could use the measurements as below

Post in thread '[T6_measured] Monitoring DPF regeneration, DPF condition, EGR operation'

6 Aug 2023

Indeed the particle sensor is registering something...

Did you also get any of the faults codes?

P226D00 - Particle filter damaged or substrate missing Intermittently
P24B100 - Particle sensor measurement electrode short-circuit to positive pole Intermittently
P24B000 - Particle sensor measurement electrode short-circuit to ground Intermittently

Zoomed in​

Well below the 10 minutes...

• mmi

• 

 

[KPanch98]

All understood, thank you @mmi . I got a video of the blowby to show you - does this look excessive to you? Also checked oil level and it looks just fine.

Booking in with a garage for next week. Let's hope they know their stuff!

Thanks

 

[mmi]

I got a video of the blowby to show you - does this look excessive to you?

I would say it's just normal.