2.0 TDI CRLB frequent regeneration

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gregga
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Joined: Tue Feb 22, 2022 2:23 pm

2.0 TDI CRLB frequent regeneration

Post by gregga » Tue Feb 22, 2022 2:38 pm

Hello,

I have an issue regarding frequent DPF regeneration which is triggered by measured soot mass.
Car: Passat B8, MY 2016, 2.0 TDI CRLB without SCR. 170kkm of mileage.

What i already did to solve problem:
replaced fuel incjectors
replaced EGR + exhaust system cleaning - old one was leaky
DPF was cleaned.
DPF sensors replaced for original ones ( i am the lucky one, who has two...)
condition of the engine was checked - nothing was found...

DPF values after cleaning:
short after regeneration - on iddle pressure : 3-4 hpa, max load: ~250hpa
when dirty - on iddle - 12-15hpa, max laod ~ 300-350hpa


The problem is that DPF regeneration is triggered by measured soot mass which is growing much faster than calculated - regeneration between 80-140km. All the rest is fine. Regeneration process runs smoothly, the only problem after is this growing measured soot mass.

Is there anything else to be checked (like sensors) before removing / replacing DPF? Do you have any idea what kind of logs could i do to check whether some sensor is not working properly even doesn't return any error?

Thanks a lot for any suggestions in advance

best regards,
Grzegorz
Last edited by gregga on Tue Feb 22, 2022 10:18 pm, edited 1 time in total.

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admin
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Re: 2.0 TDI CRLB frequent regeneration

Post by admin » Tue Feb 22, 2022 6:30 pm

I don't have direct experience, but when the calculated soot mass is replaced by the measured soot mass to trigger the regeneration, this means some sensore failure. At least based on the feedback received by users in last years. This is also the reason why many of them asked me to add the measured value that I though was useless due to its crazy values. Then I understood that this parameter become usable when there is a sensor failure. I still don't understand this strategy made by VAG engineers, but this seems the logic in these 2 parameters.
Said that, I don't know what's exactly your problem... You should try to find someone who experienced the same issue or better an expert guy that can suggest you the best solution.

Many times I see the easiest suggestion: replace every part of the system one by one, but it's not the cheapest solution for sure. Better to find the real source of the problem.
Keep us informed, this experience will be useful for many others.

gregga
Posts: 4
Joined: Tue Feb 22, 2022 2:23 pm

Re: 2.0 TDI CRLB frequent regeneration

Post by gregga » Tue Feb 22, 2022 10:32 pm

Thanks,

The only problem is every workshop i visited (including official VW) are looking for the errors. If there is no error found then the only suggestion is to replace DPF for a new one...

When i was checking the web i found some posts suggesting that EGT sensor may be the reason. Mine does not report any malfunction. I am wondering whether this is possible that it lowers or inflates the values... but according to logs all is good there. Next question, if so, is - which one.. there are at least three as far i know...
Of course the easiest way would be to replace all sensors.. but it can be a bit expensive...
Anyway there is something for sure wrong, because some time ago, before i discovered DPF problems i tuned up this car. What is important series shown 157km and 380nm what is even better than factory. After modification it was 185km and 460nm... pretty good i would say. The only problem was EGT problems on high load... then i started to look for the problem. First suggestion was to replace injections - did not help, then we opened the engine and found EGR failure and a lot of mess in intake system... all was repaired, cleaned including DPF.
After that there were still problems with EGT, so i turned back to original software - there is no problems with temperatures now...

Do you or anybody know how the VAG DPF algorithm really works - i mean from where the values are exactly being taken in order to calculate or measure the soot?

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admin
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Re: 2.0 TDI CRLB frequent regeneration

Post by admin » Wed Feb 23, 2022 7:23 pm

I've seen many times failures not reported in the ECU log, so don't trust in it. The best would be to ask to a real engine expert, not to the common service guy that we often find the the official services.

About last the question: VAG DPF simply reads parameters coming from the ECU, the calculation inside the app is only to convert the hexadecimal value into decimal using the proper formula. The values provided by the diagnostic port have been already calculated by the engine ECU, but this calculation isn't a public information.
Some parameters are easily understandable, but others are quite odd, for example the measured soot mass that comes with negative values.

andycollings
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Joined: Fri Feb 18, 2022 9:36 pm

Re: 2.0 TDI CRLB frequent regeneration

Post by andycollings » Wed Feb 23, 2022 7:54 pm

Unfortunately, your problem could be many things. The default is always to replace the DPF. As you know, this is not a cheap option. Cleaning a DPF is not always successful and can cause damage to the precious metals internally. From the research I have done on my engine 2.0 BiTDI, your post - cleaning differential pressure looks high at 250hpa. It's hard to find specific data, but I've seen lots to suggest 100hpa max. Does the pressure increase further when you drive a car? It makes sense that there shouldn't be much pressure if the exhaust gases are flowing freely through the DPF. Any kind of blockage or restriction will cause an increase.

One thing you could check is the DPF pressure sensor. There is a very useful YouTube video that takes you through how to check the voltage and operation. If that is faulty, it can give a high pressure reading, which the ECU will interpret as a blocked DPF.

gregga
Posts: 4
Joined: Tue Feb 22, 2022 2:23 pm

Re: 2.0 TDI CRLB frequent regeneration

Post by gregga » Sat Mar 19, 2022 10:16 am

Hi,

Thanks for your reply. Regarding differential pressure - it increase further... on the clean DPF (after reg.) max load increases pressure up to ~200-250 hpa and up to ~350 when dpf is full. What i also observed is that when engine (and dpf) is cold pressures are rather good. The problem starts after engine get some temperature.

Anyway - will update when there will be any progress...

Thanks.

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