DPF warning light: meaning and regeneration

The DPF (Diesel Particulate Filter) or FAP warning light applies to diesel engines fitted with a particulate filter. When it comes on, the filter is saturated or a fault has been stored. Here is the meaning and what to do.

What the DPF does

The particulate filter traps soot (particles) from the diesel engine. To prevent it from clogging, the vehicle performs regenerations: the engine injects fuel in post-combustion to burn off the soot at high temperature. Regenerations happen automatically when conditions are right (sustained revs, long enough trip).

Light on: what it means

When the light comes on (often orange), the filter is too full or a sensor (differential pressure, temperature) has reported a fault. If the light flashes or stays on despite prolonged driving, the system may be faulty: do not ignore the problem.

What to do: regeneration

Follow the handbook: usually, a steady-speed drive (main road or motorway, around 2,000–2,500 rpm) for 15–20 minutes allows automatic regeneration. Avoid switching off the engine during a regeneration (often indicated by the fan running when stopped). If the light stays on: have the system checked (fault codes, differential pressure). The garage can perform forced regeneration; if the filter is too blocked, cleaning or replacement may be needed.

Common causes and costs

Repeated short trips (town, cold engine) prevent regeneration. Differential pressure sensor faulty: about €150–350. DPF cleaning (decoking): about €200–400. DPF replacement: about €800–2,000 and more depending on vehicle. My Auto Check-up helps you prepare your visit by describing symptoms for an initial estimate.