Technical Diesel DPF or Sensor issue?

[lycopersicum]

Can you quote several pressure readings in context? Idling, accelerating, what speed etc. A single number is not informative enough.

I feel your dilemma, in the absence of the whole AdBlue delete thing the DPF would be a strong suspicion but the possibility of an unfortunate interaction with the deleted system is another strong possibility.

Once you get to this stage 2 blockage error I think you need to have the error cleared to enable another regen attempt or to indeed try any solution at all, as it's meant to force a visit to the dealer.

 

[Killykix]

We’re at a garage here in Greece. They did a forced regeneration (already our 4th one in 3 months). No soot in pipe. DPF is clean and not breached. We drove for 20min at highway and in cities, but no error fault. However, we’re convinced problem will come back.

 

[lycopersicum]

Okay. Assuming your engine is healthy and not producing abnormal amounts of soot. From this point, if your DPF is healthy, it will need a regen in about 800 km. Let's say 700 to 1200 depending on your driving conditions.

- if the error comes back in less than 700 km, the DPF probably needs changing. Or at least taken off for a deep clean in a special machine. This is not guaranteed to succeed but it can be a good occasion for the technician to evaluate the health of the DPF.

- if it comes back in more than 1200 km, and especially if the soot load is never going down, that would tend to indicate that the DPF has a normal ability to store soot and the issue is more with the regen not running properly.

- if it's in-between, it could be either.

You need to make sure your pressure sensor is working right, it should read close to zero with the engine off, respond smoothly to the gas pedal, and increase with engine load towards something in the 20 to 100 mbar range.

 

[jackwhoo]

Looking at figures in photo of scan tool .....
Average of last 5 driving regeneration times 5990seconds that is not normal

@lycopersicum

 

[Killykix]

Looking at figures in photo of scan tool .....
Average of last 5 driving regeneration times 5990seconds that is not normal

@lycopersicum

Yes, we also noticed it. We interpret it as if the car system has been trying to do the regen, but never succeeded. If this interpretation is correct, we need to understand why can’t the car launch successful regenerations. Maybe the temperature is never high enough? But not sure why…

 

[Killykix]

Okay. Assuming your engine is healthy and not producing abnormal amounts of soot. From this point, if your DPF is healthy, it will need a regen in about 800 km. Let's say 700 to 1200 depending on your driving conditions.

- if the error comes back in less than 700 km, the DPF probably needs changing. Or at least taken off for a deep clean in a special machine. This is not guaranteed to succeed but it can be a good occasion for the technician to evaluate the health of the DPF.

- if it comes back in more than 1200 km, and especially if the soot load is never going down, that would tend to indicate that the DPF has a normal ability to store soot and the issue is more with the regen not running properly.

- if it's in-between, it could be either.

You need to make sure your pressure sensor is working right, it should read close to zero with the engine off, respond smoothly to the gas pedal, and increase with engine load towards something in the 20 to 100 mbar range.

Very interesting. Last time we did a forced regeneration, we drove around 1200km before it came back, from Bulgaria to Southern Greece.

Have you seen the picture I attached earlier (hereby attached gain)? It does seem that the car system doesn’t manage to run regen (last time it tried for 1h40 regen instead of 15min), but we can’t understand why.

It believe pressure sensor is working properly. The garage just reset it again, it’s brand new and gives low reading when idle.

We will anyway follow your advice and go to a DPF cleaner. I guess it can only be beneficial, although I’m not sure it’ll solve the issue (if regen isn’t happening, a clean DPF won’t help)

 

[lycopersicum]

Interesting indeed. Are you able to monitor the soot load while driving? Eg if the error comes after 1200 km and no regen attempt (soot load just keeps increasing) the DPF itself could be fine, the problem is elsewhere. Vs coming after 1200 km but several regens in that interval (soot load goes down, but creeps up higher every time), then DPF is a likely culprit.

 

[Killykix]

Interesting indeed. Are you able to monitor the soot load while driving? Eg if the error comes after 1200 km and no regen attempt (soot load just keeps increasing) the DPF itself could be fine, the problem is elsewhere. Vs coming after 1200 km but several regens in that interval (soot load goes down, but creeps up higher every time), then DPF is a likely culprit.

Hello, after driving 1300km, the problem came back, same error code and limp mode.

We bought an OBD reader to give us live data:
- No passive regeneration ever occurs, even on highways. Because of that, soot load increases steadily (around +40% in 1h30 of driving)
- As passive regen doesn’t work, ECU triggers an active regen as an emergency which works correctly and reduces soot load back to ~15%, confirming that the DPF itself is functional and not physically clogged.
- Exhaust Gas Temperature Sensor 1 (pre-DPF) is consistently lower than Sensor 2 (post-DPF) during normal driving, which is abnormal (it typically averages around 250–300°C, with short peaks around 350–380°C, which seems too low)
- ⁠The ECU keeps trying to launch a passive regen, but conditions are never validated
- During active regeneration, Sensor 2 becomes significantly hotter than Sensor 1, which is also abnormal

All this shows that the DPF is not the root cause; it regenerates successfully when forced. The system is effectively operating in “emergency mode”, allowing soot to rise to 100% before forcing active regeneration.

There seem to be a structural thermal issue upstream of the DPF preventing normal passive regeneration.

What do you think?

 

[jackwhoo]

100% soot load is not fully loaded with soot, it is the point at which regeneration should occur.
It is a bit of a misleading naming of the parameter

 

[lycopersicum]

As far as I can tell your last post describes a normally functioning system.

There is no practical possibility of passive regen on a Ducato. It just doesn't get hot enough. Even a long climb on the highway barely reaches 450-500 °C. All regens are either active (while driving at 100% soot, which is the normal behaviour) or forced (at the workshop).

Downstream gets hotter than upstream because of the injected fuel that gets burned inside the DPF via catalytic action. That's also normal.

So the focus must now turn on to the pressure sensor values. What pressure do you read at idle, when driving, before and after a regen, etc?

 

[lycopersicum]

With the active regen system confirmed to function normally, that leaves only 2 possibilities:

1. the error comes up because the sensor is reading aberrant values -- to test this, can you share a graph or recording over a typical drive? Do the values vary smoothly with engine load and within what range?

2. the error comes up because the differential pressure increases faster than the soot load (which is based on mileage, and therefore blind to the real clogging). Normally, the soot load should trigger a regen before the pressure can reach the error threshold. If the DPF is degraded (or excessive soot is being produced) the pressure can reach the error threshold before the (theoretical) soot load reaches 100%. There's normally a backup system that can trigger an "emergency" active regen before 100% in response to unexpectedly high pressure, but if the DPF is too degraded the strain of the regen can be enough to reach the error threshold, I suppose.

Given what you've shared so far I lean towards option 2.

 

[Killykix]

Thank you for all the info. I’ll try to answer all your points:

1. I understand that downstream sensor gets hotter during a regen due to injections, but is it normal that it’s also hotter during normal drive without regen? I’ve always read that temperature pre-DPF should be higher, not the other way around

2. Attached are 2 graphs: IMG2907 is a drive on national roads and smaller roads (uphills), including idle time, no regeneration. Pressure is at 3 kpa (30mbar) when idle, peaks above 40kpa sometimes. Soot load is increasing extremely fast, no? (From 15% to 70% in 40km). IMG2910: 1h drive on faster roads, with an active regen launched at the end. I’m also including the temperature evolution of sensor 1 and 2 for that drive.

Our average distance between regen is calculated at 144km, which sounds way too low. Do you think that everything works normally, but our problem is that we produce too much soot? What would be the cause?

Thank you for your help and your time

 

[Killykix]

Based on our conversation, here are our main suspects:

1. Soot accumulates way too fast due to an unknown cause that needs to be identified (EGR valve or injector #6 not working properly as per the error code P1206 (22))
2. ⁠Gas exhaust temperature values aberrant because of either broken sensor 1 and/or leak somewhere pre-DPF
3. ⁠DPF physically clogged that can’t be cleaned via regen and need physical cleaning
4. ⁠DPF broken

as a reminder, DPF pressure sensor was recently replaced (Bosch brand).

Are the assumptions above correct?

 

[lycopersicum]

Thanks for the data.

First of all the pressure sensor itself looks healthy. The signal makes sense, it's not too noisy, etc.

The pressure values are very high. I see 100-200 mbar at 60 km/h at the start of the graph where the soot load is supposed to be low. These are values one would only expect to see when the DPF is full of soot and the engine working hard. Peaks in excess of 400 mbar later on shouldn't happen in a healthy system. 30 mbar at idle is also very high.

If you're certain that the sensor is the right type for your model, it sure does look like the DPF is blocking up heavily.

Re: the DPF temperatures, I don't want to read too much into it as there are many factors involved. The important thing is, 10 minutes at 600°C sounds fine for an active regen. I also see the pressure falling sharply afterwards. So the active regens are working and doing their job.

I cannot fully explain the speed at which the soot load value increases based on my knowledge of the older Euro 5 system. My best guess would be that your newer ECU is smarter in its calculation and takes the actual pressure into consideration. That fast increase certainly seems consistent with reality given the high pressures. One thing to double check here: does your coolant reach a stable temperature while cruising and how hot does it get?

As the regens are working and everything else seems consistent, I see only two explanations:
- DPF is degraded and can only hold a little bit of soot before it starts to block the exhaust
- engine is producing lots of soot all the time

It could be either or it could be both; I don't feel super confident I can distinguish between the two based on sensor data. So it certainly seems like a good idea to have the injection and EGR system checked as well.

 

[Killykix]

Not sure why but my OBD didn’t record coolant temperature in the former driving sessions I shared. I could only find the one attached, which is the very first recording I did with the OBD (which didn’t record data continuously for some reason). I believe it seems more or less stable?

We haven’t been to a DPF specialist yet as we keep reading stories about people cleaning it manually only to get the engine light back on shortly after, but maybe it’s time to inspect it.

If engine is indeed producing lots of soot at all time, if I understand correctly the causes could be EGR valve and/or injector #6 (as stated on the error code)? Any other cause I should look into?

We need to drive to a mechanic here in Crete and try to fix it once and for all. We are currently stuck in mountain roads in limp mode, the next city is behind uphill roads… that’s gonna be a challenge, hopefully we can make it.