DPF Issues: Troubleshooting with VCDS & VAG DPF App

Hello valued community,



Here are a few facts about the car.

- Caddy Maxi 4Motion

- Year of manufacture: 2013

- 2.0 TDI engine (CFHF) (original 110 hp)

- Mileage approximately 105,000 km.

- Software tuning since 2017 (50,000 km).



"For a few months now, I've been having a problem where it's constantly regenerating. I noticed it because the fan is always running. Since the start of the pandemic, I've been doing a lot of short trips due to working from home, so I initially thought that might be the cause. (There were no problems from 2017 to 2020)."

Over the past few weeks, I've had to drive hundreds of kilometers on the highway, and the problem persists. I'd like to get to the bottom of it.



I've also noticed that the car often smells like burnt diesel, either after being turned off or even inside the cabin when at an intersection, even without any regeneration having taken place.


I wanted to troubleshoot some issues using an OBD dongle, the "VAG DPF" app, and VCDS.





I've noticed the following.

- Regeneration every 50-70 km.

- After registration, soot mass calculation, approximately 5g.

- Shortly before registration, Soot Mass Calculation, approximately 21-23g.

- Oil ash volume: 0.07 l

-You can almost watch in real-time as the percentage indicator for the filling level increases and the soot mass calculation rises.

- Differential pressure varies between 1-200 hPa depending on the load.

- Regarding "Soot Mass Measured," a negative value is displayed (which seems very unusual).

The values in VCDS and the app are the same.


"I also noticed that only one hose is connected to the differential pressure sensor; the other port has only a very short piece of tubing attached. I did some research on this and found a few threads where people said that this is perfectly normal. I also can't imagine why the previous owner would have tampered with the DPF with only 45,000 km on the odometer."


I would like to hear some opinions and ideas about this error message. I'm wondering if the DPF is simply full and needs to be replaced, or if there might be other underlying issues.


Thank you in advance.



Best regards,



Felix.

The short tube on the differential pressure sensor is normal. It simply measures the ambient pressure.

If it produces implausible values, you might want to retrain the learning parameters.

Can you read the fuel injection quantity deviation of the injectors?

Hello,

Yes, current differential pressure sensors typically have only one hose connected.
That's normal; the "other side" is calculated using a model based on the parameters in the ECU and the ambient pressure.

If your DPF is regenerated and the soot level drops to zero or nearly zero during the process, then the DPF and its associated sensors are likely okay.

The question is whether the differential pressure sensor is measuring incorrectly, or whether too much soot is being produced.

See typical values for the differential pressure sensor.

Possible causes for excessive soot during driving:
- Leak in the charge air system (intercooler/hoses), which can be identified by oily spots.
- Issues with the EGR valve.

If you measure a high air mass with VCDS while the actual boost pressure is too low, you can assume there is a leak in the charge air system.

Best regards, Rainer.

No, it stops the regeneration process when the calculated soot mass reaches approximately 5 grams.

The differential pressure is a maximum of 200 hPa. I will log this again.

What still makes me suspicious is the negative value shown for "soot mass measured." I once checked another Caddy (with a different license plate code), and it showed a positive value there.

I will try troubleshooting with VCDS again later.


What I'm going to try to check.
-Injector quantity deviation via VCDS.
- Leak in the charge air duct.
- Log air mass and boost pressure.

The differences between the "calculated soot load" and the "measured soot load" are normal, and it is also normal for one of these values to be negative after regeneration. Usually, this is the value for the "measured soot load".
Why?
The maximum soot mass or loading limit for field regeneration in a 4-cylinder engine is just under 24 grams. If the loading limit is reached, regardless of which of the two values is exceeded, regeneration is triggered.
During the regeneration process, both values naturally decrease. The regeneration is considered successful when a "midpoint" of approximately zero is reached. The difference can be reduced through forced regenerations and similar methods, but that's not the issue here.
You're experiencing a problem where the "calculated soot mass" value increases too quickly, even on the highway.
Behind this value lies a lot of information: operating profile, driving profile, sensor data. If you have a very heavy foot and accelerate frequently, the load will increase more quickly than with a constant load. If you constantly drive near the emission limit, that will also affect the value.
You can start by checking all the sensors connected to the engine for plausibility, including temperature sensors, pressure sensors, and the oxygen sensor.
hg
Herbert.

Hello.

This weekend, I finally managed to do a "log" recording. I created two log files containing sensor data, as suggested. I cleaned up the CSV files a bit to make them more readable.

The routes were mostly a few kilometers long, consisting largely of travel in rural areas and within towns.

Log 1
- Engine speed
- Vehicle speed
- Differential pressure
- Time since last registration.
- Calculated soot mass.
- Measured soot mass.
- Distance traveled since last registration.

Log 2
- Engine speed
- Vehicle speed
-Target boost pressure
- Actual boost pressure value.
- Air mass value
- Air mass setpoint.
-Fuel injection quantity deviation, cylinders 1-4.

Please upload the CSV file again in its original form. Do not make any changes or conversions. This way, we can view the log using VScope.

Do you already have a SCR cat?

Nordhesse_Lukas wrote:

Could you please upload the CSV file again in its original form? Please don't make any changes or conversions. This way, we can view the log using VScope.

He doesn't need it either, because he can use KDataScope. The conversion still doesn't make sense and usually only causes problems.