Why is my DPF warning light on?
DPF warning light: what it means and what to do
The short answer
The diesel particulate filter (DPF) traps soot from the exhaust and burns it off when the exhaust gets hot enough, a process called regeneration. The warning light means soot has built up faster than the filter can clear it. Sometimes a longer drive sorts it. If the light stays on, something is usually stopping regeneration or producing too much soot, and that cause needs finding before anyone sells you a new filter.
Common causes
- Lots of short, slow journeys, so the exhaust never gets hot enough to regenerate
- A faulty differential pressure sensor, or a split or blocked sensor pipe giving false readings
- Injector, EGR or turbo faults making the engine produce extra soot
- The wrong engine oil: most DPF diesels need low-ash oil to the maker’s specification
- Ash build-up on high-mileage filters, which regeneration cannot burn off
What not to do
Do not keep driving for weeks with the light on, and do not let anyone remove the filter. A vehicle with its DPF removed is illegal to use on the road and fails its MOT.
What to do now
- Check your handbook: many makers advise a sustained drive at motorway speed to trigger a regeneration.
- If the light stays on, or comes back quickly, book a diagnosis rather than a new filter.
- Tell us how the car is used (short trips, towing, mileage) and whether the oil was changed recently.
Draft Technical wording to be reviewed by PK before publishing.