Subaru Diesel Particulate Filter

  • July 14, 2016
  • Niazi Helou
  • Director

Subaru Diesel DPF "Diesel Particulate Filter" Explained

Subaru-Diesel-Particulate-Filter Our technical people are often asked about the Subaru Diesel Particulate Filter and the lights that sometimes appear on the instrument cluster relating to the DPF System.

Some questions asked include:

  • What is the purpose of the Diesel Particulate filter?
  • How does it work?
  • What are error codes P1469, P1466, and P1468
  • Why does the exhaust light flash on my instrument display?
  • How do I fix this system when it fails?
We hope here to provide a basic understanding of the Subaru Diesel system and the effects of the diesel particulate filter with a few precautions that should be observed. The Subaru EE20 Diesel boxer engine incorporates common rail high fuel pressure fuel technology that produces high output while reducing fuel consumption. However, this high pressure system also creates unburned diesel exhaust particles smaller than 0.05 microns, which pose a health risk to humans.

What is the purpose of the "DPF" Diesel Particulate filter?

In Summary the DPF is responsible for trapping Diesel particulates that escape through the combustion process without being consumed or burnt. These particulates are stored in the DPF until enough heat is generated in the exhaust system to burn them off.

How does it work?

Exhaust gas is passed through the diesel oxidation catalyst after combustion and under normal driving where exhaust temperature is between approximately 150 – 400 degrees exhaust particles burn off. City vehicles driven constantly at speeds lower than 80 kilometres per hour, tend to accumulate soot in the DPF and engine management system intervention is needed to raise exhaust temperature. Soot accumulation will produce a warning light, in which case the driver should drive the vehicle for some time at higher speeds, or rev the engine while standing to burn off the particles. If this is not done and soot continues to accumulate the DPF will need to be cleaned or replaced. subaroo There are various Diagnostic Trouble Codes (DTC) for Subaru diesel systems related to the "DPF" Diesel Particulate filter.
  • DTC P1469 Limp Home normally indicates a blocked DPF. In this case an in depth diagnosis is required to determine whether the filter requires replacing or another fault exists. Please note: other defective components such as faulty injectors or an incorrectly operating Exhaust Gas Recirculation (EGR) system, as well as multiple aborted regenerations can cause a blocked filter.
  • DTC P1466 normally represents some type of leak within the DPF. However when this DTC is present other items should also be considered rather than just concluding that a leak must be present.
  • DTC P1468 is related to engine oil dilution. Oil Dilution is calculated based on the injection period when regenerating to eliminate soot. High values normally indicate low exhaust temperature from low engine speed stop-start driving.

Why does the exhaust light flash on my instrument display?

Constant illumination of the DPF symbol usually indicates that soot storage is above a certain level and that the temperature required to burn the soot particles off has not been achieved. It may also be that the regeneration has been interrupted several times; this can happen due to stop-start driving conditions. If the accumulation of the soot drops away due to to a change in driving technique, (normally a vehicle speed greater then 70kmh for 20 mins), then the "DPF" Diesel Particulate Light will extinguish. A DPF flashing light usually indicates that the soot accumulation is too high for ECU intervention. It also indicates that the driver has ignored the speed request light for at least 1500kms. At this time a method known as "Forced Regeneration" is required to burn the soot off. This usually means driving to your nearest Subaru service centre to complete this process. An ignored Flashing DPF can become a costly repair as soot levels of the filter will rise beyond the possibility of a simple clean out. In this case the DPF will flash alongside the engine light or MIL light logging code: DTC P1469.

A replacement DPF is expensive. Is there a cheaper option?

Yes, in most cases we can dramatically reduce the repair cost for this system.
It is important that a correct diagnosis is made when analysing at Subaru diesel problems to avoid un-necessary costly repairs. Our experienced Subaru mechanics can provide an accurate, obligation free quote. If your DPF has failed, and is clogged too badly for regenerative processes to clear, you once had only one option: a new DPF. At over $3000 for supply and installation, this represents a major expense. All Drive Subaroo can now clean out your DPF at a fraction of the cost of replacement, and the cleaned unit, absent other damage, will be as good as new.

We offer two services:

  • Exchange unit. We have fully cleaned DPF units in stock and can have you up and running in one day.
  • Clean your unit. We can remove, clean and replace your exiting DPF unit. In this case allow three days for turnaround. DAS is an NRMA Roadside Subaru suggested repairer.

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