Soot and ash
Soot is carbon that burns at high temperatures. Ash comes mainly from oil additives and does not burn. Regeneration deals with soot; ash slowly accumulates over the filter's life, which is one reason high-mileage DPFs eventually need cleaning or replacement.
The three kinds of regeneration
Passive regeneration
On sustained faster runs the exhaust gets hot enough to burn soot continuously, with no intervention from the engine control unit. Motorway driving does this naturally.
Active regeneration
When the control unit calculates the filter is loaded, it raises exhaust temperature — typically by changing injection — for a period. Signs can include a raised idle, the cooling fan running after switch-off, a hot smell or stop-start being disabled. Switching off mid-regeneration interrupts it.
Forced regeneration
Started with diagnostic equipment, usually with the vehicle stationary and monitored. It is appropriate only when soot loading is within safe limits and no fault is preventing regeneration.
Why regeneration fails
Short journeys are the classic cause: the engine never runs long or hot enough for an active regeneration to finish. But faults matter just as much. Faulty differential pressure or temperature sensors give the control unit wrong information; an EGR, injector or turbo fault can increase soot production; a thermostat stuck open can keep temperatures low; and some vehicles will not regenerate with a low fuel level or another active fault.
- 01Short trips and interrupted regenerations
- 02Sensor and sensor-pipe faults
- 03EGR, injector or turbo faults
- 04Low engine temperature
- 05Other active faults inhibiting regeneration
Helping your DPF
Follow the handbook's advice, especially regarding warning lights. Include a regular longer run at steady speed if your use is mostly short trips. Use the oil specification the manufacturer requires — low-ash oils exist for DPF-equipped engines. And do not ignore warnings: a heavily loaded filter is harder to recover.
Using this guide
This guide is general and educational. Vehicles differ in their engines, control units, software and emissions equipment, and manufacturers' handbooks sometimes give specific instructions that take priority over general advice. If anything here conflicts with your handbook or a warning on your dashboard, follow the handbook and get the vehicle checked.
We do not use customer stories or invented figures in our guides. Where something depends on the individual vehicle, we say so.
How we approach DPF advice
Diagnosis comes before parts or software. We read stored fault codes, look at live data such as sensor readings, temperatures and pressures where the system makes them available, and ask how and when the problem appears. A warning light describes a symptom that the control unit has detected; it does not always name the part that has failed, so the fault code is the starting point of the investigation rather than the answer.
Once we understand the likely cause we explain the findings in plain language and discuss the sensible options, which might be a repair, a clean, a software update, a replacement part or simply a change in how the vehicle is used. You receive a quote for the agreed scope before further work goes ahead. We will not recommend removing an emissions system as a fix for a road vehicle.
What to send us before booking DPF advice
The quickest way to get useful advice is to send the registration and a short description by WhatsApp or through the quote form. Support and suitability vary by engine, gearbox, control unit and software version, so a registration lets us check the right information instead of guessing. Any estimate given remotely is provisional until the vehicle has been seen and the required checks are complete.
- 01Vehicle registration and approximate mileage
- 02Make, model and engine size, if known
- 03Any warning lights, messages, symptoms or fault codes
- 04Existing remaps, tuning boxes or hardware modifications
- 05How the vehicle is used — commuting, towing, short trips or heavy loads
- 06Whether the vehicle is currently in limp mode or will not start
Visiting the workshop for DPF advice
All work is carried out at our single workshop at Unit 2, Lancaster Works, Kingsbridge Road, Manchester M9 5SP. We do not run a mobile remapping service and we have no other branches, so every DPF advice enquiry is booked into the same Manchester workshop. Visits are by arrangement: please call or WhatsApp before travelling so we can confirm the vehicle, the time and what the visit will involve.
Access is through the black gate. Call when you arrive so we can let you in, then keep left towards the rear of the site. We are open Monday to Friday 8am–6pm and Saturday 8am–1pm, and closed on Sunday. If the vehicle is in limp mode, showing a serious warning or will not start, tell us before setting off so we can talk about whether it is sensible to drive it or whether transport should be arranged.