A neighbor recently had his VW’s DPF removed, cleaned, and refitted. However, the DPF light remains on and the car is in limp mode, even after attempting a forced regeneration using VCDS. This article explores the diagnostic process and potential solutions.
VCDS Scan Results and Initial Steps
A VCDS scan revealed the following fault codes:
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16856 – Particle Filter P2463 00 [175] – Excessive Soot Accumulation: This code indicates a significant buildup of soot in the DPF, triggering the MIL (Malfunction Indicator Lamp). Freeze frame data showed a soot mass measured (MASS_SOOT_PHY_PF) of 40.00g.
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14356 – Exhaust Gas Temperature Sensor 4 Bank 1 P246E 00 [167] – Electrical Malfunction: This code points to a potential issue with the exhaust gas temperature sensor, which is crucial for DPF regeneration. This code appeared after the attempted forced regeneration.
Following the Ross-Tech Wiki guide for Diesel Particle Filter Emergency Regeneration on a 1.6l/2.0l R4 CR-TDI (UDS) engine, a forced regeneration was initiated using Adaptation Channel “Service regeneration of particulate filter while driving” due to the unavailability of the “Service regeneration of particle filter” option.
Forced Regeneration and Further Observations
A 45-minute test drive was conducted while monitoring measuring blocks IDE00434 and IDE00435. IDE00434 (calculated soot mass) remained constant at 54.60g. IDE00435 (measured soot mass) decreased from 75.12g to 11.63g during the drive.
Despite the apparent reduction in soot mass observed in IDE00435, the DPF light persists, limp mode remains active, and the measured soot mass in the engine scan (MASS_SOOT_PHY_PF) remains unchanged at 40.00g.
A new exhaust gas temperature sensor was installed, but yielded the same results. Basic settings relearning procedures were also unsuccessful.
Potential Causes and Next Steps
The discrepancy between the decreasing soot mass observed in measuring block IDE00435 and the static value in the fault code data (MASS_SOOT_PHY_PF) suggests a potential issue with the DPF pressure sensor or related wiring. The persistent fault code 16856, even after a seemingly successful regeneration, further supports this possibility.
The appearance of the exhaust gas temperature sensor fault code (14356) after the forced regeneration may indicate a pre-existing issue exacerbated by the regeneration process or a separate problem altogether. Further investigation into the sensor’s wiring and functionality is necessary.
Other potential causes to consider include:
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DPF Pressure Hoses: Leaks or blockages in the pressure hoses can disrupt the pressure readings and hinder regeneration.
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DPF Differential Pressure Sensor: A faulty differential pressure sensor can provide inaccurate readings, preventing proper regeneration.
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Wiring Harness Issues: Damaged or corroded wiring in the DPF system can cause communication errors and malfunction.
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Software or Coding Issues: Incorrect software or coding within the engine control module could be preventing proper DPF operation.
Further diagnostics should focus on:
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Checking DPF pressure sensor readings and comparing them to expected values.
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Inspecting DPF pressure hoses for leaks or blockages.
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Thoroughly examining the wiring harness for damage or corrosion.
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Consulting with a VW specialist to rule out software or coding issues.
Resolving the underlying issue causing the persistent DPF light and limp mode will likely require a systematic approach to diagnose and address each potential cause.
