Volkswagen Multivan Diesel Particulate Filter DPF T4 (1990-2003)

The DPF on the Volkswagen Multivan T4 (produced 1989-2003) is an anti-pollution device fitted in the exhaust system after the catalytic converter and before the silencer. It traps up to 99 % of fine soot particles from diesel combustion, reducing harmful emissions and health risks caused by particulates.

The DPF is made of a ceramic body containing around 50 microscopic channels per cm² which trap soot particles while allowing exhaust gases to pass. There are two types of regeneration to clean the filter:

• Passive regeneration occurs naturally at high exhaust temperatures (e.g., highway driving) burning soot to CO2, water vapour and ash.
• Active regeneration is triggered by the engine control unit when backpressure rises, using post-injection, EGR valve and turbo to heat gases to approx. 600°C for 5-15 minutes, typically every 500-700 km. This is vital for city or short trips where passive regeneration is insufficient.

Some DPFs use additives to lower combustion temperature of soot by about 100°C to help regeneration at lower loads, though AdBlue is generally not used on T4 models.

The DPF is mainly fitted on the 2.5 TDI 88 hp engine (code AJT) in Multivan T4 models, compliant with Euro emission standards up to Euro 5 in late models. Its construction features silicon carbide material with specific OEM part numbers. Regular replacement is recommended every 120,000 km with a maximum ash load capacity of 60 g.

Regeneration specifics include:

• Road regeneration requires sustained exhaust temperatures for 22-30 minutes at speeds between 60-80 km/h.
• Manual or emergency regeneration can be forced via diagnostic tools like VCDS/VAG-COM, either while stationary or driving.

Manual regeneration is important especially for frequent short or urban trips where the DPF risks clogging.

Signs you might have a clogged or failing DPF include:

• Increased fuel consumption due to higher backpressure on the engine.
• Loss of engine power and reduced torque.
• Illumination of the Check Engine light or specific DPF warning light indicating soot overload.
• High differential pressure detected by sensors, worsened by prolonged low RPM driving.

Ignoring these symptoms can cause engine damage and increased emissions.

Maintenance focuses on regular regeneration and avoiding extended periods of low-speed, short trips:

• Ensure you occasionally drive at higher speeds for at least 22-30 minutes to allow passive regeneration.
• If the DPF warning appears, use a diagnostic tool to force active regeneration promptly.
• Chemical cleaning products like DPF cleaners can assist but must be compatible and used according to instructions.
• Replacement is recommended every 120,000 km or as dictated by ash accumulation and diagnostic checks.

Always follow vehicle and product manufacturer instructions to avoid damage or warranty issues.

Several product types exist for cleaning and replacement:

• DPF cleaning sprays (aerosols) with chemical agents suitable for soot removal.
• Catalytic converter and DPF cleaning fluids for injection into the exhaust system.
• Complete original or equivalent DPF units for fitting when replacement is necessary.

Prices vary depending on product type and supplier. Always select replacements compatible with your engine code and Euro standard. For best quality and warranty, use products certified to meet or exceed OEM technical standards.

Short, low-speed journeys cause insufficient exhaust gas temperatures needed for passive regeneration, resulting in soot accumulation. This leads to frequent active regeneration cycles or clogging if the DPF cannot clean itself properly. Symptoms worsen if driving conditions keep the engine at low RPMs for extended periods.

• Regular longer drives at motorway speeds help maintain DPF functionality.
• For urban use, manual regeneration using diagnostic equipment is recommended.

Regularly maintaining proper DPF function reduces vehicle emissions and avoids costly repairs.

For precise diagnostics and genuine professional advice on your DPF system, consult an authorised Volkswagen garage or use dedicated diagnostic tools such as VCDS. These tools can confirm sensor readings, perform forced regenerations, and check system pressures and faults.

• Consult product manuals and follow official installation and maintenance instructions.
• Use professional support for technical assistance, warranty claims, or replacement advice.

Professional service ensures the DPF is kept in optimal condition, maximising performance and reducing environmental impact.

Remember to regularly read your vehicle's on-board diagnostics and never ignore warning lights related to the DPF system.