Subaru Impreza Diesel Particulate Filter DPF

The Diesel Particulate Filter (DPF) on Subaru Impreza diesel models, such as the 2.0 D (GR/GH, engine code EE20Z), is an anti-pollution device located in the exhaust system after the catalytic converter and before the silencer. It is designed to capture up to 99% of fine soot particles produced by diesel combustion, which are harmful and carcinogenic. The DPF is mandatory on modern diesel engines to comply with emission standards.

The DPF filters exhaust gases through a ceramic body composed of about 50 microscopic channels per cm². Soot accumulates on the channel walls, forming a layer that improves filtration efficiency but also creates back pressure, potentially reducing engine power. To maintain performance, the DPF undergoes regeneration to burn off soot.

• Passive regeneration: Natural soot combustion at high exhaust temperatures during prolonged high-load driving (e.g., motorway).
• Active regeneration: Injecting extra fuel and modifying engine parameters to raise exhaust temperature above 500-600°C, burning soot rapidly. This usually occurs every 500-700 km for 5-15 minutes under certain conditions such as low engine load.

Some filters also use additives to lower soot combustion temperature and AdBlue injection reduces NOx emissions, working alongside the DPF.

The DPF system includes the ceramic particulate filter housed within stainless steel casing. Sensors monitor its condition and enable regeneration:

• Temperature sensors measure exhaust gas temperature before and after the DPF.
• Pressure differential sensors detect soot buildup by measuring pressure drop across the filter.
• EGR (Exhaust Gas Recirculation) valve controls NOx levels and interacts with regeneration.

Sensors are commonly located downstream of the turbocharger and before and after the DPF unit.

The original equipment manufacturer (OEM) reference numbers for Subaru Impreza diesel particulate filters are:

• 44612AA502
• 44612AA503
• 44612AA504

These numbers correspond to DPF units compatible with the 2.0 D diesel engine in models GR and GH equipped with EE20Z engine code.

The DPF warning light (usually an orange or black exhaust symbol) indicates excessive soot accumulation or back pressure in the filter. Common causes include:

• Frequent short trips or urban driving not allowing passive regeneration.
• Faulty sensors reporting incorrect data.
• Malfunctioning EGR valve or turbocharger issues.
• Long-term clogging by residual ash that cannot be burned off by regeneration.

It is essential to perform a diagnostic check when this light appears to prevent engine damage or reduced power.

Yes, a forced regeneration can be initiated via diagnostic tools such as Launch scanners used on Subaru Forester and similar diesel models. This process manually raises exhaust temperature to burn off soot deposits effectively.

• Useful if the DPF is clogged but the automatic regeneration did not complete.
• Typically performed by a qualified mechanic or specialist using proper equipment.
• Can potentially clear temporary soot buildup and turn off the warning light.

Note: If the DPF is loaded with hard residual ash, forced regeneration may not be effective and professional cleaning or replacement might be required.

Proper vehicle use and maintenance reduce DPF clogging risks and extend filter life:

• Drive regularly at sustained motorway speeds to promote passive regeneration.
• Use recommended engine oil and fuel quality to minimize soot production.
• Follow manufacturer service intervals for oil and spark plug changes.
• Address DPF warning lights early with a diagnostic check and possible regeneration.
• Avoid frequent short trips that prevent the engine reaching proper operating temperature.

Adhering to these can help keep your DPF clean and your diesel engine running efficiently.

Krosfou offers brand-new, high-performance DPFs for Subaru Impreza diesel models, manufactured in Europe with a 3-year warranty and full compliance with emission standards.

• Produced with stainless steel INOX 409 and high-quality ceramic monoliths.
• Certified by TÜV SÜD ensuring reliability and performance equal or superior to OEM parts.
• Supplied with installation materials, mounting instructions, and homologation certification upon request.
• Technical support available for installation guidance and diagnostics.

Choosing genuine Krosfou DPFs ensures the best quality, durability, and compliance while helping reduce your vehicle’s emissions responsibly.