DPF not regenerating (Articles)

The DPF (Diesel Particulate Filter) often cannot be regenerated, and the amount of soot continues to build up until a forced regeneration is necessary. If you wait too long and the soot load is too high, the diesel particulate filter must be replaced because regeneration is no longer possible or makes sense in the vehicle. The corresponding measured values from the engine control unit can be checked using VCDS.
The following conditions must be met for the DPF to be normally regenerated by the engine control unit:
- Coolant temperature is sufficient (thermostat is functioning correctly).
- If installed: Oil level sensor/oil temperature sensor in the oil pan must be functional. Oil temperature and oil level must be sufficient.
- The differential pressure sensor at the DPF is functional and the values are within the normal range (see the collection of values for DPF differential pressures).
- Temperature sensors on the turbocharger and DPF are functioning correctly.
- AGR functional (not always necessary depending on the engine, but it definitely facilitates regeneration as the engine warms up noticeably faster).

Even if the conditions mentioned above are met, the DPF can still become overloaded due to excessive soot or smoke generation from the engine.
- Leak in the intake air system, indicated by noticeably high measured air mass values despite normal or low actual boost pressure.
- Bodged tuning / DIY tuning / Makeshift tuning
- Damage to the turbocharger or engine, oil mist in the exhaust stream.

Since the oxygen sensor is located between the turbocharger and the DPF, this should manifest as lower oxygen sensor readings under load, compared to identical, properly functioning vehicles.