Blocked DPF: symptoms, regeneration, cost and affected cars

The diesel particulate filter (DPF) traps soot; it cleans itself by burning it off during "regenerations", which need a high exhaust temperature. In town, on short trips, that temperature is never reached: the filter gradually blocks (GetCarwise, Ford C-Max; GetCarwise, Ford Fusion). It is one of the most expensive weak points of modern diesels (Caradisiac).

Symptoms of a blocked DPF

• DPF, emissions or engine warning light on;
• loss of power, sometimes limp mode (L'argus, cited for the Ford Kuga);
• very frequent regenerations, cooling fan running after switch-off (CarVerif, Audi Q3).

Why it blocks

Blockage comes mostly from use: a Peugeot 2.0 BlueHDi owner reports a DPF replaced at 48,000 km because the previous owner did too much town driving (Fiches-auto). On the diesel Audi Q3, the filter clogs between 60,000 and 80,000 km in urban use (CarVerif). A diesel that has regularly done motorway miles offers much better conditions to the DPF and the EGR valve (Fiches-auto, Audi A3).

An interrupted regeneration can also dilute fuel into the oil, whose level then slowly rises (What Car?, cited for the Dacia Duster). The EGR valve, linked to the DPF, often clogs at the same time (FixMyCar).

Is it serious?

Do not let it drag on: a blocked DPF creates back pressure that heats the turbo and can cause oil leaks in it; FixMyCar puts the average turbo repair at £747 (FixMyCar). Replacing the filter itself is expensive: €800 to €1,500 reported on the BMW 5 Series E60 (CarVerif).

How to avoid it

• Regularly drive on a fast road: regeneration needs an exhaust temperature that town driving does not reach (GetCarwise, Ford C-Max).
• If you only drive in town, a diesel is probably not the right choice: see diesel or petrol on a used car.

Before buying a used diesel

An engine warning light, loss of power, frequent regenerations or a fan that often runs after switch-off call for a diagnosis before buying (CarVerif, Audi Q3). Ask how the car was used (town or open road) and for DPF-related invoices.