How to read parameters

All the information below is based on information gathered from the internet and personal experience.

1. Software Version

The software version of the engine control unit (ECU) affects the frequency of DPF regeneration. For example, in an Audi A4 B8, post-Dieselgate software versions are numbered: 9977, 9978, 9979, 9980, and 9981. This leads to more frequent DPF regenerations (every 250-300 km). The calculated soot mass increases at a faster rate compared to ECUs with lower software versions.

2. Oil Ash Residue

This value indicates the amount of ash filling the filter. This value is not burned off and increases with the vehicle's mileage. Depending on the engine, this value is given in liters or grams. For 2.0 TDI engines, the maximum ash fill value is 0.175L or 60g. Exceeding these values may require filter replacement or cleaning, but not always. It depends on driving style and routes.

3. Temperature Before and After the DPF

During normal driving, temperatures do not exceed 350°C. With dynamic driving, the temperature can reach up to 450°C. During regeneration, temperatures range from 550 to 700°C.

• Passive Regeneration: A spontaneous DPF regeneration that occurs when the temperature exceeds 350 degrees. My observations suggest that passive regeneration can also happen at lower temperatures, resulting in a decrease in the measured soot mass.
• Active Regeneration: A DPF regeneration forced by the ECU. For the filter to regenerate properly, the minimum temperature should be 580 degrees. If the car does not reach this temperature during regeneration, it indicates a problem with the ancillary equipment.

To achieve the correct temperatures, you should not accelerate aggressively or use engine braking (as this turns off the additional fuel injection for DPF regeneration). You should maintain a steady speed within the 2,000-2,500 RPM range.

4. Differential Pressure

This is the most important parameter for assessing DPF clogging. Based on this value, you can determine the overall health of your filter.

Measurement methods:

• At idle (1-15 hPa);
• At idle while increasing RPM to 2.5k-3k (10-30 hPa);
• While driving in higher gears with the accelerator pedal to the floor;

Option (c) is the most relevant, as it is the only way to accurately check the extent of DPF clogging.

To perform the test, the best method is to engage 3rd gear and press the accelerator to the floor. The measurement should be taken up to approximately 4,000 RPM. The values recorded at 4,000 RPM should be interpreted according to the following table:

4a. Differential Pressure Offset

This parameter indicates sensor health. The value should be close to zero.

5. Kilometers Since Last Regeneration

Shows distance since last regeneration. Typically ranges from 200 km to 800–1000 km depending on vehicle. After regeneration, this value resets to zero.

6. Soot Mass Calculated

This is the soot mass calculated by the ECU. Based on this value, regeneration should start when the value reaches 14g to 24g. This value should always be higher than the measured soot mass. After regeneration, the calculated soot mass drops to around 2.5-5g.

My observations show that for cars driven more in the city, regeneration tends to start closer to the 24g limit. However, during highway driving, if the engine conditions are right, regeneration might start earlier (even before 20g).

For cars with pre-Dieselgate software, it's possible to initiate regeneration using cruise control. If the DPF temperature is around 300 degrees (during a highway drive) and the calculated mass is above 14g, the ECU will see that the conditions are right and will initiate a DPF regeneration within a few seconds or minutes.

Using cruise control for regeneration has another advantage: when regenerating without it, the process usually ends around 5g. With cruise control, the DPF regenerates longer, down to about 2.5g, resulting in a more thorough cleaning.

7. Soot Mass Measured

The measured soot mass should never increase faster than the calculated mass. If this happens (e.g., calculated soot mass is 11g and measured is 18g), it may indicate a problem with the engine's ancillary equipment or the filter itself. This value is calculated based on engine load, engine speed, and, most importantly, differential pressure.

When the measured value increases faster, it triggers the regeneration process, and the measured and calculated soot values equalize. After regeneration, the value drops to 0g or can even be negative (in which case you could say the DPF is in better condition than the ECU expects).