A vehicle in limp mode with a persistent Diesel Particulate Filter (DPF) light can be frustrating. This case study examines a forced DPF regeneration attempt using VCDS (Vag-Com Diagnostic System) on a 1.6l TDI engine after a manual DPF cleaning. We’ll analyze the VCDS scan data, the regeneration process, and potential reasons why the issue persists.
Understanding the VCDS Scan
The initial VCDS scan reveals two fault codes:
-
16856 – Particle Filter (P2463): Excessive Soot Accumulation. This code indicates the DPF is overloaded with soot, triggering the DPF light and limp mode. Key data points include:
- Soot Mass Measured (MASS_SOOT_PHY_PF): 40.00 g. This is the physical soot accumulation measured by the DPF sensor.
- Soot Mass Calculated (MASS_SOOT_SIM_PF): 29.40 g. This is the calculated soot load based on engine operating conditions. The discrepancy between measured and calculated values can indicate sensor issues.
- Distance Since Last Regeneration (DIST_RGN_ENVD_H): 130 km. This shows the distance driven since the last successful regeneration.
-
14356 – Exhaust Gas Temperature Sensor 4 Bank 1 (P246E): Electrical Malfunction. This code, appearing after the forced regeneration attempt, suggests a problem with the exhaust gas temperature sensor, crucial for monitoring DPF regeneration temperatures.
The Forced Regeneration Process
Following the Ross-Tech wiki guide for forced DPF regeneration on a 1.6l/2.0l R4 CR-TDI (UDS) engine, the “Service Regeneration of Particulate Filter While Driving” adaptation channel was used due to the unavailability of the “Service Regeneration” option.
During the 45-minute drive, monitoring measuring blocks IDE00434 (calculated soot mass) and IDE00435 (measured soot mass) showed a decrease in IDE00435 from 75.12g to 11.63g. However, the MASS_SOOT_PHY_PF value in the engine scan remained at 40.00g.
Why Didn’t the Forced Regeneration Work?
Despite the observed decrease in measured soot mass during the drive, the persistent DPF light and limp mode suggest the regeneration was unsuccessful. Several possibilities exist:
- Faulty DPF Pressure Sensor: The discrepancy between the decreasing IDE00435 and the static MASS_SOOT_PHY_PF suggests a potential issue with the DPF pressure sensor. Even with a clean DPF, a faulty sensor can report incorrect soot levels, preventing successful regeneration completion.
- Exhaust Gas Temperature Sensor Issue: The P246E fault code indicates a problem with the exhaust gas temperature sensor. Accurate temperature readings are crucial for controlling and monitoring the regeneration process. A malfunctioning sensor can disrupt the process.
- DPF Cleaning Issues: While the DPF was cleaned, it’s possible the cleaning wasn’t thorough enough, or damage occurred during removal and refitting.
- Other Underlying Issues: Other potential problems, such as fuel injector issues or boost leaks, can contribute to excessive soot generation and hinder regeneration.
Conclusion
Performing a forced regeneration with VCDS requires careful monitoring and diagnosis. In this case, the unchanging MASS_SOOT_PHY_PF value and the appearance of the exhaust gas temperature sensor fault code point to potential sensor issues. Further diagnostics, focusing on the DPF pressure sensor and the exhaust gas temperature sensor, are necessary to pinpoint the root cause and resolve the DPF issue. Addressing these sensor problems, along with verifying the integrity of the DPF and ruling out other contributing factors, is crucial for restoring proper vehicle operation.
